1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
|
---
stage: none
group: unassigned
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/product/ux/technical-writing/#assignments
---
# GraphQL API style guide
This document outlines the style guide for the GitLab [GraphQL API](../api/graphql/index.md).
## How GitLab implements GraphQL
<!-- vale gitlab.Spelling = NO -->
We use the [GraphQL Ruby gem](https://graphql-ruby.org/) written by [Robert Mosolgo](https://github.com/rmosolgo/).
In addition, we have a subscription to [GraphQL Pro](https://graphql.pro/). For
details see [GraphQL Pro subscription](graphql_guide/graphql_pro.md).
<!-- vale gitlab.Spelling = YES -->
All GraphQL queries are directed to a single endpoint
([`app/controllers/graphql_controller.rb#execute`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app%2Fcontrollers%2Fgraphql_controller.rb)),
which is exposed as an API endpoint at `/api/graphql`.
## Deep Dive
In March 2019, Nick Thomas hosted a Deep Dive (GitLab team members only: `https://gitlab.com/gitlab-org/create-stage/issues/1`)
on the GitLab [GraphQL API](../api/graphql/index.md) to share domain-specific knowledge
with anyone who may work in this part of the codebase in the future. You can find the
<i class="fa fa-youtube-play youtube" aria-hidden="true"></i>
[recording on YouTube](https://www.youtube.com/watch?v=-9L_1MWrjkg), and the slides on
[Google Slides](https://docs.google.com/presentation/d/1qOTxpkTdHIp1CRjuTvO-aXg0_rUtzE3ETfLUdnBB5uQ/edit)
and in [PDF](https://gitlab.com/gitlab-org/create-stage/uploads/8e78ea7f326b2ef649e7d7d569c26d56/GraphQL_Deep_Dive__Create_.pdf).
Everything covered in this deep dive was accurate as of GitLab 11.9, and while specific
details may have changed since then, it should still serve as a good introduction.
## GraphiQL
GraphiQL is an interactive GraphQL API explorer where you can play around with existing queries.
You can access it in any GitLab environment on `https://<your-gitlab-site.com>/-/graphql-explorer`.
For example, the one for [GitLab.com](https://gitlab.com/-/graphql-explorer).
## Authentication
Authentication happens through the `GraphqlController`, right now this
uses the same authentication as the Rails application. So the session
can be shared.
It's also possible to add a `private_token` to the query string, or
add a `HTTP_PRIVATE_TOKEN` header.
## Limits
Several limits apply to the GraphQL API and some of these can be overridden
by developers.
### Max page size
By default, [connections](#connection-types) can only return
at most a maximum number of records defined in
[`app/graphql/gitlab_schema.rb`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/graphql/gitlab_schema.rb)
per page.
Developers can [specify a custom max page size](#page-size-limit) when defining
a connection.
### Max complexity
Complexity is explained [on our client-facing API page](../api/graphql/index.md#max-query-complexity).
Fields default to adding `1` to a query's complexity score, but developers can
[specify a custom complexity](#field-complexity) when defining a field.
The complexity score of a query [can itself be queried for](../api/graphql/getting_started.md#query-complexity).
### Request timeout
Requests time out at 30 seconds.
### Limit maximum field call count
In some cases, you want to prevent the evaluation of a specific field on multiple parent nodes
because it results in an N+1 query problem and there is no optimal solution. This should be
considered an option of last resort, to be used only when methods such as
[lookahead to preload associations](#look-ahead), or [using batching](graphql_guide/batchloader.md)
have been considered.
For example:
```graphql
# This usage is expected.
query {
project {
environments
}
}
# This usage is NOT expected.
# It results in N+1 query problem. EnvironmentsResolver can't use GraphQL batch loader in favor of GraphQL pagination.
query {
projects {
nodes {
environments
}
}
}
```
To prevent this, you can use the `Gitlab::Graphql::Limit::FieldCallCount` extension on the field:
```ruby
# This allows maximum 1 call to the `environments` field. If the field is evaluated on more than one node,
# it raises an error.
field :environments do
extension(::Gitlab::Graphql::Limit::FieldCallCount, limit: 1)
end
```
or you can apply the extension in a resolver class:
```ruby
module Resolvers
class EnvironmentsResolver < BaseResolver
extension(::Gitlab::Graphql::Limit::FieldCallCount, limit: 1)
# ...
end
end
```
When you add this limit, make sure that the affected field's `description` is also updated accordingly. For example,
```ruby
field :environments,
description: 'Environments of the project. This field can only be resolved for one project in any single request.'
```
## Breaking changes
The GitLab GraphQL API is [versionless](https://graphql.org/learn/best-practices/#versioning) which means
developers must familiarize themselves with our [Deprecation and Removal process](../api/graphql/index.md#deprecation-and-removal-process).
Breaking changes are:
- Removing or renaming a field, argument, enum value, or mutation.
- Changing the type of a field, argument or enum value.
- Raising the [complexity](#max-complexity) of a field or complexity multipliers in a resolver.
- Changing a field from being _not_ nullable (`null: false`) to nullable (`null: true`), as
discussed in [Nullable fields](#nullable-fields).
- Changing an argument from being optional (`required: false`) to being required (`required: true`).
- Changing the [max page size](#page-size-limit) of a connection.
- Lowering the global limits for query complexity and depth.
- Anything else that can result in queries hitting a limit that previously was allowed.
See the [deprecating schema items](#deprecating-schema-items) section for how to deprecate items.
### Breaking change exemptions
Schema items [marked as alpha](#mark-schema-items-as-alpha) are exempt from the deprecation process,
and can be removed or changed at any time without notice.
## Global IDs
The GitLab GraphQL API uses Global IDs (i.e: `"gid://gitlab/MyObject/123"`)
and never database primary key IDs.
Global ID is [a convention](https://graphql.org/learn/global-object-identification/)
used for caching and fetching in client-side libraries.
See also:
- [Exposing Global IDs](#exposing-global-ids).
- [Mutation arguments](#object-identifier-arguments).
- [Deprecating Global IDs](#deprecate-global-ids).
We have a custom scalar type (`Types::GlobalIDType`) which should be used as the
type of input and output arguments when the value is a `GlobalID`. The benefits
of using this type instead of `ID` are:
- it validates that the value is a `GlobalID`
- it parses it into a `GlobalID` before passing it to user code
- it can be parameterized on the type of the object (for example,
`GlobalIDType[Project]`) which offers even better validation and security.
Consider using this type for all new arguments and result types. Remember that
it is perfectly possible to parameterize this type with a concern or a
supertype, if you want to accept a wider range of objects (such as
`GlobalIDType[Issuable]` vs `GlobalIDType[Issue]`).
## Types
We use a code-first schema, and we declare what type everything is in Ruby.
For example, `app/graphql/types/issue_type.rb`:
```ruby
graphql_name 'Issue'
field :iid, GraphQL::Types::ID, null: true
field :title, GraphQL::Types::String, null: true
# we also have a method here that we've defined, that extends `field`
markdown_field :title_html, null: true
field :description, GraphQL::Types::String, null: true
markdown_field :description_html, null: true
```
We give each type a name (in this case `Issue`).
The `iid`, `title` and `description` are _scalar_ GraphQL types.
`iid` is a `GraphQL::Types::ID`, a special string type that signifies a unique ID.
`title` and `description` are regular `GraphQL::Types::String` types.
Note that the old scalar types `GraphQL:ID`, `GraphQL::INT_TYPE`, `GraphQL::STRING_TYPE`,
`GraphQL:BOOLEAN_TYPE`, and `GraphQL::FLOAT_TYPE` are no longer allowed. Please use `GraphQL::Types::ID`,
`GraphQL::Types::Int`, `GraphQL::Types::String`, `GraphQL::Types::Boolean`, and `GraphQL::Types::Float`.
When exposing a model through the GraphQL API, we do so by creating a
new type in `app/graphql/types`. You can also declare custom GraphQL data types
for scalar data types (for example `TimeType`).
When exposing properties in a type, make sure to keep the logic inside
the definition as minimal as possible. Instead, consider moving any
logic into a presenter:
```ruby
class Types::MergeRequestType < BaseObject
present_using MergeRequestPresenter
name 'MergeRequest'
end
```
An existing presenter could be used, but it is also possible to create
a new presenter specifically for GraphQL.
The presenter is initialized using the object resolved by a field, and
the context.
### Nullable fields
GraphQL allows fields to be "nullable" or "non-nullable". The former means
that `null` may be returned instead of a value of the specified type. **In
general**, you should prefer using nullable fields to non-nullable ones, for
the following reasons:
- It's common for data to switch from required to not-required, and back again
- Even when there is no prospect of a field becoming optional, it may not be **available** at query time
- For instance, the `content` of a blob may need to be looked up from Gitaly
- If the `content` is nullable, we can return a **partial** response, instead of failing the whole query
- Changing from a non-nullable field to a nullable field is difficult with a versionless schema
Non-nullable fields should only be used when a field is required, very unlikely
to become optional in the future, and very easy to calculate. An example would
be `id` fields.
A non-nullable GraphQL schema field is an object type followed by the exclamation point (bang) `!`. Here's an example from the `gitlab_schema.graphql` file:
```graphql
id: ProjectID!
```
Here's an example of a non-nullable GraphQL array:
```graphql
errors: [String!]!
```
Further reading:
- [GraphQL Best Practices Guide](https://graphql.org/learn/best-practices/#nullability).
- GraphQL documentation on [Object types and fields](https://graphql.org/learn/schema/#object-types-and-fields).
- [Using nullability in GraphQL](https://www.apollographql.com/blog/graphql/basics/using-nullability-in-graphql/)
### Exposing Global IDs
In keeping with the GitLab use of [Global IDs](#global-ids), always convert
database primary key IDs into Global IDs when you expose them.
All fields named `id` are
[converted automatically](https://gitlab.com/gitlab-org/gitlab/-/blob/b0f56e7/app/graphql/types/base_object.rb#L11-14)
into the object's Global ID.
Fields that are not named `id` need to be manually converted. We can do this using
[`Gitlab::GlobalID.build`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/global_id.rb),
or by calling `#to_global_id` on an object that has mixed in the
`GlobalID::Identification` module.
Using an example from
[`Types::Notes::DiscussionType`](https://gitlab.com/gitlab-org/gitlab/-/blob/3c95bd9/app/graphql/types/notes/discussion_type.rb#L24-26):
```ruby
field :reply_id, GraphQL::Types::ID
def reply_id
::Gitlab::GlobalId.build(object, id: object.reply_id)
end
```
### Connection types
NOTE:
For specifics on implementation, see [Pagination implementation](#pagination-implementation).
GraphQL uses [cursor based pagination](https://graphql.org/learn/pagination/#pagination-and-edges)
to expose collections of items. This provides the clients with a lot
of flexibility while also allowing the backend to use different
pagination models.
To expose a collection of resources we can use a connection type. This wraps the array with default pagination fields. For example a query for project-pipelines could look like this:
```graphql
query($project_path: ID!) {
project(fullPath: $project_path) {
pipelines(first: 2) {
pageInfo {
hasNextPage
hasPreviousPage
}
edges {
cursor
node {
id
status
}
}
}
}
}
```
This would return the first 2 pipelines of a project and related
pagination information, ordered by descending ID. The returned data would
look like this:
```json
{
"data": {
"project": {
"pipelines": {
"pageInfo": {
"hasNextPage": true,
"hasPreviousPage": false
},
"edges": [
{
"cursor": "Nzc=",
"node": {
"id": "gid://gitlab/Pipeline/77",
"status": "FAILED"
}
},
{
"cursor": "Njc=",
"node": {
"id": "gid://gitlab/Pipeline/67",
"status": "FAILED"
}
}
]
}
}
}
}
```
To get the next page, the cursor of the last known element could be
passed:
```graphql
query($project_path: ID!) {
project(fullPath: $project_path) {
pipelines(first: 2, after: "Njc=") {
pageInfo {
hasNextPage
hasPreviousPage
}
edges {
cursor
node {
id
status
}
}
}
}
}
```
To ensure that we get consistent ordering, we append an ordering on the primary
key, in descending order. This is usually `id`, so we add `order(id: :desc)`
to the end of the relation. A primary key _must_ be available on the underlying table.
#### Shortcut fields
Sometimes it can seem easy to implement a "shortcut field", having the resolver return the first of a collection if no parameters are passed.
These "shortcut fields" are discouraged because they create maintenance overhead.
They need to be kept in sync with their canonical field, and deprecated or modified if their canonical field changes.
Use the functionality the framework provides unless there is a compelling reason to do otherwise.
For example, instead of `latest_pipeline`, use `pipelines(last: 1)`.
#### Page size limit
By default, the API returns at most a maximum number of records defined in
[`app/graphql/gitlab_schema.rb`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/graphql/gitlab_schema.rb)
per page in a connection and this is also the default number of records
returned per page if no limiting arguments (`first:` or `last:`) are provided by a client.
The `max_page_size` argument can be used to specify a different page size limit
for a connection.
WARNING:
It's better to change the frontend client, or product requirements, to not need large amounts of
records per page than it is to raise the `max_page_size`, as the default is set to ensure
the GraphQL API remains performant.
For example:
```ruby
field :tags,
Types::ContainerRepositoryTagType.connection_type,
null: true,
description: 'Tags of the container repository',
max_page_size: 20
```
### Field complexity
The GitLab GraphQL API uses a _complexity_ score to limit performing overly complex queries.
Complexity is described in [our client documentation](../api/graphql/index.md#max-query-complexity) on the topic.
Complexity limits are defined in [`app/graphql/gitlab_schema.rb`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/graphql/gitlab_schema.rb).
By default, fields add `1` to a query's complexity score. This can be overridden by
[providing a custom `complexity`](https://graphql-ruby.org/queries/complexity_and_depth.html) value for a field.
Developers should specify higher complexity for fields that cause more _work_ to be performed
by the server to return data. Fields that represent data that can be returned
with little-to-no _work_, for example in most cases; `id` or `title`, can be given a complexity of `0`.
### `calls_gitaly`
Fields that have the potential to perform a [Gitaly](../administration/gitaly/index.md) call when resolving _must_ be marked as
such by passing `calls_gitaly: true` to `field` when defining it.
For example:
```ruby
field :blob, type: Types::Snippets::BlobType,
description: 'Snippet blob',
null: false,
calls_gitaly: true
```
This increments the [`complexity` score](#field-complexity) of the field by `1`.
If a resolver calls Gitaly, it can be annotated with
`BaseResolver.calls_gitaly!`. This passes `calls_gitaly: true` to any
field that uses this resolver.
For example:
```ruby
class BranchResolver < BaseResolver
type ::Types::BranchType, null: true
calls_gitaly!
argument name: ::GraphQL::Types::String, required: true
def resolve(name:)
object.branch(name)
end
end
```
Then when we use it, any field that uses `BranchResolver` has the correct
value for `calls_gitaly:`.
### Exposing permissions for a type
To expose permissions the current user has on a resource, you can call
the `expose_permissions` passing in a separate type representing the
permissions for the resource.
For example:
```ruby
module Types
class MergeRequestType < BaseObject
expose_permissions Types::MergeRequestPermissionsType
end
end
```
The permission type inherits from `BasePermissionType` which includes
some helper methods, that allow exposing permissions as non-nullable
booleans:
```ruby
class MergeRequestPermissionsType < BasePermissionType
graphql_name 'MergeRequestPermissions'
present_using MergeRequestPresenter
abilities :admin_merge_request, :update_merge_request, :create_note
ability_field :resolve_note,
description: 'Indicates the user can resolve discussions on the merge request.'
permission_field :push_to_source_branch, method: :can_push_to_source_branch?
end
```
- **`permission_field`**: Acts the same as `graphql-ruby`'s
`field` method but setting a default description and type and making
them non-nullable. These options can still be overridden by adding
them as arguments.
- **`ability_field`**: Expose an ability defined in our policies. This
behaves the same way as `permission_field` and the same
arguments can be overridden.
- **`abilities`**: Allows exposing several abilities defined in our
policies at once. The fields for these must all be non-nullable
booleans with a default description.
## Feature flags
You can implement [feature flags](../development/feature_flags/index.md) in GraphQL to toggle:
- The return value of a field.
- The behavior of an argument or mutation.
This can be done in a resolver, in the
type, or even in a model method, depending on your preference and
situation.
NOTE:
It's recommended that you also [mark the item as Alpha](#mark-schema-items-as-alpha) while it is behind a feature flag.
This signals to consumers of the public GraphQL API that the field is not
meant to be used yet.
You can also
[change or remove Alpha items at any time](#breaking-change-exemptions) without needing to deprecate them. When the flag is removed, "release"
the schema item by removing its Alpha property to make it public.
### Descriptions for feature-flagged items
When using a feature flag to toggle the value or behavior of a schema item, the
`description` of the item must:
- State that the value or behavior can be toggled by a feature flag.
- Name the feature flag.
- State what the field returns, or behavior is, when the feature flag is disabled (or
enabled, if more appropriate).
### Examples of using feature flags
#### Feature-flagged field
A field value is toggled based on the feature flag state. A common use is to return `null` if the feature flag is disabled:
```ruby
field :foo, GraphQL::Types::String, null: true,
alpha: { milestone: '10.0' },
description: 'Some test field. Returns `null`' \
'if `my_feature_flag` feature flag is disabled.'
def foo
object.foo if Feature.enabled?(:my_feature_flag, object)
end
```
#### Feature-flagged argument
An argument can be ignored, or have its value changed, based on the feature flag state.
A common use is to ignore the argument when a feature flag is disabled:
```ruby
argument :foo, type: GraphQL::Types::String, required: false,
alpha: { milestone: '10.0' },
description: 'Some test argument. Is ignored if ' \
'`my_feature_flag` feature flag is disabled.'
def resolve(args)
args.delete(:foo) unless Feature.enabled?(:my_feature_flag, object)
# ...
end
```
#### Feature-flagged mutation
A mutation that cannot be performed due to a feature flag state is handled as a
[non-recoverable mutation error](#failure-irrelevant-to-the-user). The error is returned at the top level:
```ruby
description 'Mutates an object. Does not mutate the object if ' \
'`my_feature_flag` feature flag is disabled.'
def resolve(id: )
object = authorized_find!(id: id)
raise Gitlab::Graphql::Errors::ResourceNotAvailable, '`my_feature_flag` feature flag is disabled.' \
if Feature.disabled?(:my_feature_flag, object)
# ...
end
```
## Deprecating schema items
The GitLab GraphQL API is versionless, which means we maintain backwards
compatibility with older versions of the API with every change.
Rather than removing fields, arguments, [enum values](#enums), or [mutations](#mutations),
they must be _deprecated_ instead.
The deprecated parts of the schema can then be removed in a future release
in accordance with the [GitLab deprecation process](../api/graphql/index.md#deprecation-and-removal-process).
To deprecate a schema item in GraphQL:
1. [Create a deprecation issue](#create-a-deprecation-issue) for the item.
1. [Mark the item as deprecated](#mark-the-item-as-deprecated) in the schema.
See also:
- [Aliasing and deprecating mutations](#aliasing-and-deprecating-mutations).
- [Marking schema items as Alpha](#mark-schema-items-as-alpha).
- [How to filter Kibana for queries that used deprecated fields](graphql_guide/monitoring.md#queries-that-used-a-deprecated-field).
### Create a deprecation issue
Every GraphQL deprecation should have a deprecation issue created [using the `Deprecations` issue template](https://gitlab.com/gitlab-org/gitlab/-/issues/new?issuable_template=Deprecations) to track its deprecation and removal.
Apply these two labels to the deprecation issue:
- `~GraphQL`
- `~deprecation`
### Mark the item as deprecated
Fields, arguments, enum values, and mutations are deprecated using the `deprecated` property. The value of the property is a `Hash` of:
- `reason` - Reason for the deprecation.
- `milestone` - Milestone that the field was deprecated.
Example:
```ruby
field :token, GraphQL::Types::String, null: true,
deprecated: { reason: 'Login via token has been removed', milestone: '10.0' },
description: 'Token for login.'
```
The original `description` of the things being deprecated should be maintained,
and should _not_ be updated to mention the deprecation. Instead, the `reason`
is appended to the `description`.
#### Deprecation reason style guide
Where the reason for deprecation is due to the field, argument, or enum value being
replaced, the `reason` must indicate the replacement. For example, the
following is a `reason` for a replaced field:
```plaintext
Use `otherFieldName`
```
Examples:
```ruby
field :designs, ::Types::DesignManagement::DesignCollectionType, null: true,
deprecated: { reason: 'Use `designCollection`', milestone: '10.0' },
description: 'The designs associated with this issue.',
```
```ruby
module Types
class TodoStateEnum < BaseEnum
value 'pending', deprecated: { reason: 'Use PENDING', milestone: '10.0' }
value 'done', deprecated: { reason: 'Use DONE', milestone: '10.0' }
value 'PENDING', value: 'pending'
value 'DONE', value: 'done'
end
end
```
If the field, argument, or enum value being deprecated is not being replaced,
a descriptive deprecation `reason` should be given.
#### Deprecate Global IDs
We use the [`rails/globalid`](https://github.com/rails/globalid) gem to generate and parse
Global IDs, so as such they are coupled to model names. When we rename a
model, its Global ID changes.
If the Global ID is used as an _argument_ type anywhere in the schema, then the Global ID
change would normally constitute a breaking change.
To continue to support clients using the old Global ID argument, we add a deprecation
to `Gitlab::GlobalId::Deprecations`.
NOTE:
If the Global ID is _only_ [exposed as a field](#exposing-global-ids) then we do not need to
deprecate it. We consider the change to the way a Global ID is expressed in a field to be
backwards-compatible. We expect that clients don't parse these values: they are meant to
be treated as opaque tokens, and any structure in them is incidental and not to be relied on.
**Example scenario:**
This example scenario is based on this [merge request](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/62645).
A model named `PrometheusService` is to be renamed `Integrations::Prometheus`. The old model
name is used to create a Global ID type that is used as an argument for a mutation:
```ruby
# Mutations::UpdatePrometheus:
argument :id, Types::GlobalIDType[::PrometheusService],
required: true,
description: "The ID of the integration to mutate."
```
Clients call the mutation by passing a Global ID string that looks like
`"gid://gitlab/PrometheusService/1"`, named as `PrometheusServiceID`, as the `input.id` argument:
```graphql
mutation updatePrometheus($id: PrometheusServiceID!, $active: Boolean!) {
prometheusIntegrationUpdate(input: { id: $id, active: $active }) {
errors
integration {
active
}
}
}
```
We rename the model to `Integrations::Prometheus`, and then update the codebase with the new name.
When we come to update the mutation, we pass the renamed model to `Types::GlobalIDType[]`:
```ruby
# Mutations::UpdatePrometheus:
argument :id, Types::GlobalIDType[::Integrations::Prometheus],
required: true,
description: "The ID of the integration to mutate."
```
This would cause a breaking change to the mutation, as the API now rejects clients who
pass an `id` argument as `"gid://gitlab/PrometheusService/1"`, or that specify the argument
type as `PrometheusServiceID` in the query signature.
To allow clients to continue to interact with the mutation unchanged, edit the `DEPRECATIONS` constant in
`Gitlab::GlobalId::Deprecations` and add a new `Deprecation` to the array:
```ruby
DEPRECATIONS = [
Gitlab::Graphql::DeprecationsBase::NameDeprecation.new(old_name: 'PrometheusService', new_name: 'Integrations::Prometheus', milestone: '14.0')
].freeze
```
Then follow our regular [deprecation process](../api/graphql/index.md#deprecation-and-removal-process). To later remove
support for the former argument style, remove the `Deprecation`:
```ruby
DEPRECATIONS = [].freeze
```
During the deprecation period the API will accept either of these formats for the argument value:
- `"gid://gitlab/PrometheusService/1"`
- `"gid://gitlab/Integrations::Prometheus/1"`
The API will also accept these types in the query signature for the argument:
- `PrometheusServiceID`
- `IntegrationsPrometheusID`
NOTE:
Although queries that use the old type (`PrometheusServiceID` in this example) will be
considered valid and executable by the API, validator tools will consider them to be invalid.
This is because we are deprecating using a bespoke method outside of the
[`@deprecated` directive](https://spec.graphql.org/June2018/#sec--deprecated), so validators are not
aware of the support.
The documentation will mention that the old Global ID style is now deprecated.
## Mark schema items as Alpha
You can mark GraphQL schema items (fields, arguments, enum values, and mutations) as
[Alpha](https://about.gitlab.com/handbook/product/gitlab-the-product/#alpha-beta-ga).
An item marked as Alpha is [exempt from the deprecation process](#breaking-change-exemptions) and can be removed
at any time without notice. Mark an item as Alpha when it is
subject to change and not ready for public use.
NOTE:
Only mark new items as Alpha. Never mark existing items
as Alpha because they're already public.
To mark a schema item as Alpha, use the `alpha:` keyword.
You must provide the `milestone:` that introduced the Alpha item.
For example:
```ruby
field :token, GraphQL::Types::String, null: true,
alpha: { milestone: '10.0' },
description: 'Token for login.'
```
Alpha GraphQL items is a custom GitLab feature that leverages GraphQL deprecations. An Alpha item
appears as deprecated in the GraphQL schema. Like all deprecated schema items, you can test an
Alpha field in [GraphiQL](../api/graphql/index.md#graphiql). However, be aware that the GraphiQL
autocomplete editor doesn't suggest deprecated fields.
The item shows as Alpha in our generated GraphQL documentation and its GraphQL schema description.
## Enums
GitLab GraphQL enums are defined in `app/graphql/types`. When defining new enums, the
following rules apply:
- Values must be uppercase.
- Class names must end with the string `Enum`.
- The `graphql_name` must not contain the string `Enum`.
For example:
```ruby
module Types
class TrafficLightStateEnum < BaseEnum
graphql_name 'TrafficLightState'
description 'State of a traffic light'
value 'RED', description: 'Drivers must stop.'
value 'YELLOW', description: 'Drivers must stop when it is safe to.'
value 'GREEN', description: 'Drivers can start or keep driving.'
end
end
```
If the enum is used for a class property in Ruby that is not an uppercase string,
you can provide a `value:` option that adapts the uppercase value.
In the following example:
- GraphQL inputs of `OPENED` are converted to `'opened'`.
- Ruby values of `'opened'` are converted to `"OPENED"` in GraphQL responses.
```ruby
module Types
class EpicStateEnum < BaseEnum
graphql_name 'EpicState'
description 'State of a GitLab epic'
value 'OPENED', value: 'opened', description: 'An open Epic.'
value 'CLOSED', value: 'closed', description: 'A closed Epic.'
end
end
```
Enum values can be deprecated using the
[`deprecated` keyword](#deprecating-schema-items).
### Defining GraphQL enums dynamically from Rails enums
If your GraphQL enum is backed by a [Rails enum](database/creating_enums.md), then consider
using the Rails enum to dynamically define the GraphQL enum values. Doing so
binds the GraphQL enum values to the Rails enum definition, so if values are
ever added to the Rails enum then the GraphQL enum automatically reflects the change.
Example:
```ruby
module Types
class IssuableSeverityEnum < BaseEnum
graphql_name 'IssuableSeverity'
description 'Incident severity'
::IssuableSeverity.severities.keys.each do |severity|
value severity.upcase, value: severity, description: "#{severity.titleize} severity."
end
end
end
```
## JSON
When data to be returned by GraphQL is stored as
[JSON](migration_style_guide.md#storing-json-in-database), we should continue to use
GraphQL types whenever possible. Avoid using the `GraphQL::Types::JSON` type unless
the JSON data returned is _truly_ unstructured.
If the structure of the JSON data varies, but is one of a set of known possible
structures, use a
[union](https://graphql-ruby.org/type_definitions/unions.html).
An example of the use of a union for this purpose is
[!30129](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/30129).
Field names can be mapped to hash data keys using the `hash_key:` keyword if needed.
For example, given the following simple JSON data:
```json
{
"title": "My chart",
"data": [
{ "x": 0, "y": 1 },
{ "x": 1, "y": 1 },
{ "x": 2, "y": 2 }
]
}
```
We can use GraphQL types like this:
```ruby
module Types
class ChartType < BaseObject
field :title, GraphQL::Types::String, null: true, description: 'Title of the chart.'
field :data, [Types::ChartDatumType], null: true, description: 'Data of the chart.'
end
end
module Types
class ChartDatumType < BaseObject
field :x, GraphQL::Types::Int, null: true, description: 'X-axis value of the chart datum.'
field :y, GraphQL::Types::Int, null: true, description: 'Y-axis value of the chart datum.'
end
end
```
## Descriptions
All fields and arguments
[must have descriptions](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/16438).
A description of a field or argument is given using the `description:`
keyword. For example:
```ruby
field :id, GraphQL::Types::ID, description: 'ID of the issue.'
field :confidential, GraphQL::Types::Boolean, description: 'Indicates the issue is confidential.'
field :closed_at, Types::TimeType, description: 'Timestamp of when the issue was closed.'
```
You can view descriptions of fields and arguments in:
- The [GraphiQL explorer](#graphiql).
- The [static GraphQL API reference](../api/graphql/reference/index.md).
### Description style guide
#### Language and punctuation
Use `{x} of the {y}` where possible, where `{x}` is the item you're describing,
and `{y}` is the resource it applies to. For example:
```plaintext
ID of the issue.
```
Do not start descriptions with `The` or `A`, for consistency and conciseness.
End all descriptions with a period (`.`).
#### Booleans
For a boolean field (`GraphQL::Types::Boolean`), start with a verb that describes
what it does. For example:
```plaintext
Indicates the issue is confidential.
```
If necessary, provide the default. For example:
```plaintext
Sets the issue to confidential. Default is false.
```
#### `Types::TimeType` field description
For `Types::TimeType` GraphQL fields, include the word `timestamp`. This lets
the reader know that the format of the property is `Time`, rather than just `Date`.
For example:
```ruby
field :closed_at, Types::TimeType, description: 'Timestamp of when the issue was closed.'
```
### `copy_field_description` helper
Sometimes we want to ensure that two descriptions are always identical.
For example, to keep a type field description the same as a mutation argument
when they both represent the same property.
Instead of supplying a description, we can use the `copy_field_description` helper,
passing it the type, and field name to copy the description of.
Example:
```ruby
argument :title, GraphQL::Types::String,
required: false,
description: copy_field_description(Types::MergeRequestType, :title)
```
### Documentation references
Sometimes we want to refer to external URLs in our descriptions. To make this
easier, and provide proper markup in the generated reference documentation, we
provide a `see` property on fields. For example:
```ruby
field :genus,
type: GraphQL::Types::String,
null: true,
description: 'A taxonomic genus.'
see: { 'Wikipedia page on genera' => 'https://wikipedia.org/wiki/Genus' }
```
This renders in our documentation as:
```markdown
A taxonomic genus. See: [Wikipedia page on genera](https://wikipedia.org/wiki/Genus)
```
Multiple documentation references can be provided. The syntax for this property
is a `HashMap` where the keys are textual descriptions, and the values are URLs.
## Authorization
See: [GraphQL Authorization](graphql_guide/authorization.md)
## Resolvers
We define how the application serves the response using _resolvers_
stored in the `app/graphql/resolvers` directory.
The resolver provides the actual implementation logic for retrieving
the objects in question.
To find objects to display in a field, we can add resolvers to
`app/graphql/resolvers`.
Arguments can be defined within the resolver in the same way as in a mutation.
See the [Mutation arguments](#object-identifier-arguments) section.
To limit the amount of queries performed, we can use [BatchLoader](graphql_guide/batchloader.md).
### Writing resolvers
Our code should aim to be thin declarative wrappers around finders and [services](../development/reusing_abstractions.md#service-classes). You can
repeat lists of arguments, or extract them to concerns. Composition is preferred over
inheritance in most cases. Treat resolvers like controllers: resolvers should be a DSL
that compose other application abstractions.
For example:
```ruby
class PostResolver < BaseResolver
type Post.connection_type, null: true
authorize :read_blog
description 'Blog posts, optionally filtered by name'
argument :name, [::GraphQL::Types::String], required: false, as: :slug
alias_method :blog, :object
def resolve(**args)
PostFinder.new(blog, current_user, args).execute
end
end
```
While you can use the same resolver class in two different places,
such as in two different fields where the same object is exposed,
you should never re-use resolver objects directly. Resolvers have a complex life-cycle, with
authorization, readiness and resolution orchestrated by the framework, and at
each stage [lazy values](#laziness) can be returned to take advantage of batching
opportunities. Never instantiate a resolver or a mutation in application code.
Instead, the units of code reuse are much the same as in the rest of the
application:
- Finders in queries to look up data.
- Services in mutations to apply operations.
- Loaders (batch-aware finders) specific to queries.
Note that there is never any reason to use batching in a mutation. Mutations are
executed in series, so there are no batching opportunities. All values are
evaluated eagerly as soon as they are requested, so batching is unnecessary
overhead. If you are writing:
- A `Mutation`, feel free to lookup objects directly.
- A `Resolver` or methods on a `BaseObject`, then you want to allow for batching.
### Error handling
Resolvers may raise errors, which are converted to top-level errors as
appropriate. All anticipated errors should be caught and transformed to an
appropriate GraphQL error (see
[`Gitlab::Graphql::Errors`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/gitlab/graphql/errors.rb)).
Any uncaught errors are suppressed and the client receives the message
`Internal service error`.
The one special case is permission errors. In the REST API we return
`404 Not Found` for any resources that the user does not have permission to
access. The equivalent behavior in GraphQL is for us to return `null` for
all absent or unauthorized resources.
Query resolvers **should not raise errors for unauthorized resources**.
The rationale for this is that clients must not be able to distinguish between
the absence of a record and the presence of one they do not have access to. To
do so is a security vulnerability, because it leaks information we want to keep
hidden.
In most cases you don't need to worry about this - this is handled correctly by
the resolver field authorization we declare with the `authorize` DSL calls. If
you need to do something more custom however, remember, if you encounter an
object the `current_user` does not have access to when resolving a field, then
the entire field should resolve to `null`.
### Deriving resolvers (`BaseResolver.single` and `BaseResolver.last`)
For some simple use cases, we can derive resolvers from others.
The main use case for this is one resolver to find all items, and another to
find one specific one. For this, we supply convenience methods:
- `BaseResolver.single`, which constructs a new resolver that selects the first item.
- `BaseResolver.last`, which constructs a resolver that selects the last item.
The correct singular type is inferred from the collection type, so we don't have
to define the `type` here.
Before you make use of these methods, consider if it would be simpler to either:
- Write another resolver that defines its own arguments.
- Write a concern that abstracts out the query.
Using `BaseResolver.single` too freely is an anti-pattern. It can lead to
non-sensical fields, such as a `Project.mergeRequest` field that just returns
the first MR if no arguments are given. Whenever we derive a single resolver
from a collection resolver, it must have more restrictive arguments.
To make this possible, use the `when_single` block to customize the single
resolver. Every `when_single` block must:
- Define (or re-define) at least one argument.
- Make optional filters required.
For example, we can do this by redefining an existing optional argument,
changing its type and making it required:
```ruby
class JobsResolver < BaseResolver
type JobType.connection_type, null: true
authorize :read_pipeline
argument :name, [::GraphQL::Types::String], required: false
when_single do
argument :name, ::GraphQL::Types::String, required: true
end
def resolve(**args)
JobsFinder.new(pipeline, current_user, args.compact).execute
end
```
Here we have a simple resolver for getting pipeline jobs. The `name` argument is
optional when getting a list, but required when getting a single job.
If there are multiple arguments, and neither can be made required, we can use
the block to add a ready condition:
```ruby
class JobsResolver < BaseResolver
alias_method :pipeline, :object
type JobType.connection_type, null: true
authorize :read_pipeline
argument :name, [::GraphQL::Types::String], required: false
argument :id, [::Types::GlobalIDType[::Job]],
required: false,
prepare: ->(ids, ctx) { ids.map(&:model_id) }
when_single do
argument :name, ::GraphQL::Types::String, required: false
argument :id, ::Types::GlobalIDType[::Job],
required: false
prepare: ->(id, ctx) { id.model_id }
def ready?(**args)
raise ::Gitlab::Graphql::Errors::ArgumentError, 'Only one argument may be provided' unless args.size == 1
end
end
def resolve(**args)
JobsFinder.new(pipeline, current_user, args.compact).execute
end
```
Then we can use these resolver on fields:
```ruby
# In PipelineType
field :jobs, resolver: JobsResolver, description: 'All jobs.'
field :job, resolver: JobsResolver.single, description: 'A single job.'
```
### Correct use of `Resolver#ready?`
Resolvers have two public API methods as part of the framework: `#ready?(**args)` and `#resolve(**args)`.
We can use `#ready?` to perform set-up, validation or early-return without invoking `#resolve`.
Good reasons to use `#ready?` include:
- validating mutually exclusive arguments (see [validating arguments](#validating-arguments))
- Returning `Relation.none` if we know before-hand that no results are possible
- Performing setup such as initializing instance variables (although consider lazily initialized methods for this)
Implementations of [`Resolver#ready?(**args)`](https://graphql-ruby.org/api-doc/1.10.9/GraphQL/Schema/Resolver#ready%3F-instance_method) should
return `(Boolean, early_return_data)` as follows:
```ruby
def ready?(**args)
[false, 'have this instead']
end
```
For this reason, whenever you call a resolver (mainly in tests - as framework
abstractions Resolvers should not be considered re-usable, finders are to be
preferred), remember to call the `ready?` method and check the boolean flag
before calling `resolve`! An example can be seen in our [`GraphqlHelpers`](https://gitlab.com/gitlab-org/gitlab/-/blob/2d395f32d2efbb713f7bc861f96147a2a67e92f2/spec/support/helpers/graphql_helpers.rb#L20-27).
### Look-Ahead
The full query is known in advance during execution, which means we can make use
of [lookahead](https://graphql-ruby.org/queries/lookahead.html) to optimize our
queries, and batch load associations we know we need. Consider adding
lookahead support in your resolvers to avoid `N+1` performance issues.
To enable support for common lookahead use-cases (pre-loading associations when
child fields are requested), you can
include [`LooksAhead`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/graphql/resolvers/concerns/looks_ahead.rb). For example:
```ruby
# Assuming a model `MyThing` with attributes `[child_attribute, other_attribute, nested]`,
# where nested has an attribute named `included_attribute`.
class MyThingResolver < BaseResolver
include LooksAhead
# Rather than defining `resolve(**args)`, we implement: `resolve_with_lookahead(**args)`
def resolve_with_lookahead(**args)
apply_lookahead(MyThingFinder.new(current_user).execute)
end
# We list things that should always be preloaded:
# For example, if child_attribute is always needed (during authorization
# perhaps), then we can include it here.
def unconditional_includes
[:child_attribute]
end
# We list things that should be included if a certain field is selected:
def preloads
{
field_one: [:other_attribute],
field_two: [{ nested: [:included_attribute] }]
}
end
end
```
By default, fields defined in `#preloads` are preloaded if that field
is selected in the query. Occasionally, finer control may be
needed to avoid preloading too much or incorrect content.
Extending the above example, we might want to preload a different
association if certain fields are requested together. This can
be done by overriding `#filtered_preloads`:
```ruby
class MyThingResolver < BaseResolver
# ...
def filtered_preloads
return [:alternate_attribute] if lookahead.selects?(:field_one) && lookahead.selects?(:field_two)
super
end
end
```
The final thing that is needed is that every field that uses this resolver needs
to advertise the need for lookahead:
```ruby
# in ParentType
field :my_things, MyThingType.connection_type, null: true,
extras: [:lookahead], # Necessary
resolver: MyThingResolver,
description: 'My things.'
```
For an example of real world use, please
see [`ResolvesMergeRequests`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/graphql/resolvers/concerns/resolves_merge_requests.rb).
### Negated arguments
Negated filters can filter some resources (for example, find all issues that
have the `bug` label, but don't have the `bug2` label assigned). The `not`
argument is the preferred syntax to pass negated arguments:
```graphql
issues(labelName: "bug", not: {labelName: "bug2"}) {
nodes {
id
title
}
}
```
To avoid duplicated argument definitions, you can place these arguments in a reusable module (or
class, if the arguments are nested). Alternatively, you can consider to add a
[helper resolver method](https://gitlab.com/gitlab-org/gitlab/-/issues/258969).
### Metadata
When using resolvers, they can and should serve as the SSoT for field metadata.
All field options (apart from the field name) can be declared on the resolver.
These include:
- `type` (required - all resolvers must include a type annotation)
- `extras`
- `description`
- Gitaly annotations (with `calls_gitaly!`)
Example:
```ruby
module Resolvers
MyResolver < BaseResolver
type Types::MyType, null: true
extras [:lookahead]
description 'Retrieve a single MyType'
calls_gitaly!
end
end
```
### Pass a parent object into a child Presenter
Sometimes you need to access the resolved query parent in a child context to compute fields. Usually the parent is only
available in the `Resolver` class as `parent`.
To find the parent object in your `Presenter` class:
1. Add the parent object to the GraphQL `context` from your resolver's `resolve` method:
```ruby
def resolve(**args)
context[:parent_object] = parent
end
```
1. Declare that your resolver or fields require the `parent` field context. For example:
```ruby
# in ChildType
field :computed_field, SomeType, null: true,
method: :my_computing_method,
extras: [:parent], # Necessary
description: 'My field description.'
field :resolver_field, resolver: SomeTypeResolver
# In SomeTypeResolver
extras [:parent]
type SomeType, null: true
description 'My field description.'
```
1. Declare your field's method in your Presenter class and have it accept the `parent` keyword argument.
This argument contains the parent **GraphQL context**, so you have to access the parent object with
`parent[:parent_object]` or whatever key you used in your `Resolver`:
```ruby
# in ChildPresenter
def my_computing_method(parent:)
# do something with `parent[:parent_object]` here
end
# In SomeTypeResolver
def resolve(parent:)
# ...
end
```
For an example of real-world use, check [this MR that added `scopedPath` and `scopedUrl` to `IterationPresenter`](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/39543)
## Mutations
Mutations are used to change any stored values, or to trigger
actions. In the same way a GET-request should not modify data, we
cannot modify data in a regular GraphQL-query. We can however in a
mutation.
### Building Mutations
Mutations are stored in `app/graphql/mutations`, ideally grouped per
resources they are mutating, similar to our services. They should
inherit `Mutations::BaseMutation`. The fields defined on the mutation
are returned as the result of the mutation.
#### Update mutation granularity
The service-oriented architecture in GitLab means that most mutations call a Create, Delete, or Update
service, for example `UpdateMergeRequestService`.
For Update mutations, you might want to only update one aspect of an object, and thus only need a
_fine-grained_ mutation, for example `MergeRequest::SetDraft`.
It's acceptable to have both fine-grained mutations and coarse-grained mutations, but be aware
that too many fine-grained mutations can lead to organizational challenges in maintainability, code
comprehensibility, and testing.
Each mutation requires a new class, which can lead to technical debt.
It also means the schema becomes very big, and we want users to easily navigate our schema.
As each new mutation also needs tests (including slower request integration tests), adding mutations
slows down the test suite.
To minimize changes:
- Use existing mutations, such as `MergeRequest::Update`, when available.
- Expose existing services as a coarse-grained mutation.
When a fine-grained mutation might be more appropriate:
- Modifying a property that requires specific permissions or other specialized logic.
- Exposing a state-machine-like transition (locking issues, merging MRs, closing epics, etc).
- Accepting nested properties (where we accept properties for a child object).
- The semantics of the mutation can be expressed clearly and concisely.
See [issue #233063](https://gitlab.com/gitlab-org/gitlab/-/issues/233063) for further context.
### Naming conventions
Each mutation must define a `graphql_name`, which is the name of the mutation in the GraphQL schema.
Example:
```ruby
class UserUpdateMutation < BaseMutation
graphql_name 'UserUpdate'
end
```
Due to changes in the `1.13` version of the `graphql-ruby` gem, `graphql_name` should be the first
line of the class to ensure that type names are generated correctly. The `Graphql::GraphqlNamePosition` cop enforces this.
See [issue #27536](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/27536#note_840245581) for further context.
Our GraphQL mutation names are historically inconsistent, but new mutation names should follow the
convention `'{Resource}{Action}'` or `'{Resource}{Action}{Attribute}'`.
Mutations that **create** new resources should use the verb `Create`.
Example:
- `CommitCreate`
Mutations that **update** data should use:
- The verb `Update`.
- A domain-specific verb like `Set`, `Add`, or `Toggle` if more appropriate.
Examples:
- `EpicTreeReorder`
- `IssueSetWeight`
- `IssueUpdate`
- `TodoMarkDone`
Mutations that **remove** data should use:
- The verb `Delete` rather than `Destroy`.
- A domain-specific verb like `Remove` if more appropriate.
Examples:
- `AwardEmojiRemove`
- `NoteDelete`
If you need advice for mutation naming, canvass the Slack `#graphql` channel for feedback.
### Arguments
Arguments for a mutation are defined using `argument`.
Example:
```ruby
argument :my_arg, GraphQL::Types::String,
required: true,
description: "A description of the argument."
```
#### Nullability
Arguments can be marked as `required: true` which means the value must be present and not `null`.
If a required argument's value can be `null`, use the `required: :nullable` declaration.
Example:
```ruby
argument :due_date,
Types::TimeType,
required: :nullable,
description: 'The desired due date for the issue. Due date is removed if null.'
```
In the above example, the `due_date` argument must be given, but unlike the GraphQL spec, the value can be `null`.
This allows 'unsetting' the due date in a single mutation rather than creating a new mutation for removing the due date.
```ruby
{ due_date: null } # => OK
{ due_date: "2025-01-10" } # => OK
{ } # => invalid (not given)
```
#### Keywords
Each GraphQL `argument` defined is passed to the `#resolve` method
of a mutation as keyword arguments.
Example:
```ruby
def resolve(my_arg:)
# Perform mutation ...
end
```
#### Input Types
`graphql-ruby` wraps up arguments into an
[input type](https://graphql.org/learn/schema/#input-types).
For example, the
[`mergeRequestSetDraft` mutation](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/graphql/mutations/merge_requests/set_draft.rb)
defines these arguments (some
[through inheritance](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/graphql/mutations/merge_requests/base.rb)):
```ruby
argument :project_path, GraphQL::Types::ID,
required: true,
description: "The project the merge request to mutate is in."
argument :iid, GraphQL::Types::String,
required: true,
description: "The IID of the merge request to mutate."
argument :draft,
GraphQL::Types::Boolean,
required: false,
description: <<~DESC
Whether or not to set the merge request as a draft.
DESC
```
These arguments automatically generate an input type called
`MergeRequestSetDraftInput` with the 3 arguments we specified and the
`clientMutationId`.
### Object identifier arguments
In keeping with the GitLab use of [Global IDs](#global-ids), mutation
arguments should use Global IDs to identify an object and never database
primary key IDs.
Where an object has an `iid`, prefer to use the `full_path` or `group_path`
of its parent in combination with its `iid` as arguments to identify an
object rather than its `id`.
See also [Deprecate Global IDs](#deprecate-global-ids).
### Fields
In the most common situations, a mutation would return 2 fields:
- The resource being modified
- A list of errors explaining why the action could not be
performed. If the mutation succeeded, this list would be empty.
By inheriting any new mutations from `Mutations::BaseMutation` the
`errors` field is automatically added. A `clientMutationId` field is
also added, this can be used by the client to identify the result of a
single mutation when multiple are performed in a single request.
### The `resolve` method
Similar to [writing resolvers](#writing-resolvers), the `resolve` method of a mutation
should aim to be a thin declarative wrapper around a
[service](../development/reusing_abstractions.md#service-classes).
The `resolve` method receives the mutation's arguments as keyword arguments.
From here, we can call the service that modifies the resource.
The `resolve` method should then return a hash with the same field
names as defined on the mutation including an `errors` array. For example,
the `Mutations::MergeRequests::SetDraft` defines a `merge_request`
field:
```ruby
field :merge_request,
Types::MergeRequestType,
null: true,
description: "The merge request after mutation."
```
This means that the hash returned from `resolve` in this mutation
should look like this:
```ruby
{
# The merge request modified, this will be wrapped in the type
# defined on the field
merge_request: merge_request,
# An array of strings if the mutation failed after authorization.
# The `errors_on_object` helper collects `errors.full_messages`
errors: errors_on_object(merge_request)
}
```
### Mounting the mutation
To make the mutation available it must be defined on the mutation
type that is stored in `graphql/types/mutation_types`. The
`mount_mutation` helper method defines a field based on the
GraphQL-name of the mutation:
```ruby
module Types
class MutationType < BaseObject
graphql_name 'Mutation'
include Gitlab::Graphql::MountMutation
mount_mutation Mutations::MergeRequests::SetDraft
end
end
```
Generates a field called `mergeRequestSetDraft` that
`Mutations::MergeRequests::SetDraft` to be resolved.
### Authorizing resources
To authorize resources inside a mutation, we first provide the required
abilities on the mutation like this:
```ruby
module Mutations
module MergeRequests
class SetDraft < Base
graphql_name 'MergeRequestSetDraft'
authorize :update_merge_request
end
end
end
```
We can then call `authorize!` in the `resolve` method, passing in the resource we
want to validate the abilities for.
Alternatively, we can add a `find_object` method that loads the
object on the mutation. This would allow you to use the
`authorized_find!` helper method.
When a user is not allowed to perform the action, or an object is not
found, we should raise a
`Gitlab::Graphql::Errors::ResourceNotAvailable` error which is
correctly rendered to the clients.
### Errors in mutations
We encourage following the practice of
[errors as data](https://graphql-ruby.org/mutations/mutation_errors) for mutations, which
distinguishes errors by who they are relevant to, defined by who can deal with
them.
Key points:
- All mutation responses have an `errors` field. This should be populated on
failure, and may be populated on success.
- Consider who needs to see the error: the **user** or the **developer**.
- Clients should always request the `errors` field when performing mutations.
- Errors may be reported to users either at `$root.errors` (top-level error) or at
`$root.data.mutationName.errors` (mutation errors). The location depends on what kind of error
this is, and what information it holds.
- Mutation fields [must have `null: true`](https://graphql-ruby.org/mutations/mutation_errors#nullable-mutation-payload-fields)
Consider an example mutation `doTheThing` that returns a response with
two fields: `errors: [String]`, and `thing: ThingType`. The specific nature of
the `thing` itself is irrelevant to these examples, as we are considering the
errors.
There are three states a mutation response can be in:
- [Success](#success)
- [Failure (relevant to the user)](#failure-relevant-to-the-user)
- [Failure (irrelevant to the user)](#failure-irrelevant-to-the-user)
#### Success
In the happy path, errors *may* be returned, along with the anticipated payload, but
if everything was successful, then `errors` should be an empty array, because
there are no problems we need to inform the user of.
```javascript
{
data: {
doTheThing: {
errors: [] // if successful, this array will generally be empty.
thing: { .. }
}
}
}
```
#### Failure (relevant to the user)
An error that affects the **user** occurred. We refer to these as _mutation errors_.
In a _create_ mutation there is typically no `thing` to return.
In an _update_ mutation we return the current true state of `thing`. Developers may need to call `#reset` on the `thing` instance to ensure this happens.
```javascript
{
data: {
doTheThing: {
errors: ["you cannot touch the thing"],
thing: { .. }
}
}
}
```
Examples of this include:
- Model validation errors: the user may need to change the inputs.
- Permission errors: the user needs to know they cannot do this, they may need to request permission or sign in.
- Problems with application state that prevent the user's action, for example: merge conflicts, the resource was locked, and so on.
Ideally, we should prevent the user from getting this far, but if they do, they
need to be told what is wrong, so they understand the reason for the failure and
what they can do to achieve their intent, even if that is as simple as retrying the
request.
It is possible to return *recoverable* errors alongside mutation data. For example, if
a user uploads 10 files and 3 of them fail and the rest succeed, the errors for the
failures can be made available to the user, alongside the information about
the successes.
#### Failure (irrelevant to the user)
One or more *non-recoverable* errors can be returned at the _top level_. These
are things over which the **user** has little to no control, and should mainly
be system or programming problems, that a **developer** needs to know about.
In this case there is no `data`:
```javascript
{
errors: [
{"message": "argument error: expected an integer, got null"},
]
}
```
This is the result of raising an error during the mutation. In our implementation,
the messages of argument errors and validation errors are returned to the client, and all other
`StandardError` instances are caught, logged and presented to the client with the message set to `"Internal server error"`.
See [`GraphqlController`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/controllers/graphql_controller.rb) for details.
These represent programming errors, such as:
- A GraphQL syntax error, where an `Int` was passed instead of a `String`, or a required argument was not present.
- Errors in our schema, such as being unable to provide a value for a non-nullable field.
- System errors: for example, a Git storage exception, or database unavailability.
The user should not be able to cause such errors in regular usage. This category
of errors should be treated as internal, and not shown to the user in specific
detail.
We need to inform the user when the mutation fails, but we do not need to
tell them why, because they cannot have caused it, and nothing they can do
fixes it, although we may offer to retry the mutation.
#### Categorizing errors
When we write mutations, we need to be conscious about which of
these two categories an error state falls into (and communicate about this with
frontend developers to verify our assumptions). This means distinguishing the
needs of the _user_ from the needs of the _client_.
> _Never catch an error unless the user needs to know about it._
If the user does need to know about it, communicate with frontend developers
to make sure the error information we are passing back is useful.
See also the [frontend GraphQL guide](../development/fe_guide/graphql.md#handling-errors).
### Aliasing and deprecating mutations
The `#mount_aliased_mutation` helper allows us to alias a mutation as
another name in `MutationType`.
For example, to alias a mutation called `FooMutation` as `BarMutation`:
```ruby
mount_aliased_mutation 'BarMutation', Mutations::FooMutation
```
This allows us to rename a mutation and continue to support the old name,
when coupled with the [`deprecated`](#deprecating-schema-items)
argument.
Example:
```ruby
mount_aliased_mutation 'UpdateFoo',
Mutations::Foo::Update,
deprecated: { reason: 'Use fooUpdate', milestone: '13.2' }
```
Deprecated mutations should be added to `Types::DeprecatedMutations` and
tested for in the unit test of `Types::MutationType`. The merge request
[!34798](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/34798)
can be referred to as an example of this, including the method of testing
deprecated aliased mutations.
#### Deprecating EE mutations
EE mutations should follow the same process. For an example of the merge request
process, read [merge request !42588](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/42588).
## Subscriptions
We use subscriptions to push updates to clients. We use the [Action Cable implementation](https://graphql-ruby.org/subscriptions/action_cable_implementation)
to deliver the messages over websockets.
When a client subscribes to a subscription, we store their query in-memory within Puma workers. Then when the subscription is triggered,
the Puma workers execute the stored GraphQL queries and push the results to the clients.
NOTE:
We cannot test subscriptions using GraphiQL, because they require an Action Cable client, which GraphiQL does not support at the moment.
### Building subscriptions
All fields under `Types::SubscriptionType` are subscriptions that clients can subscribe to. These fields require a subscription class,
which is a descendant of `Subscriptions::BaseSubscription` and is stored under `app/graphql/subscriptions`.
The arguments required to subscribe and the fields that are returned are defined in the subscription class. Multiple fields can share
the same subscription class if they have the same arguments and return the same fields.
This class runs during the initial subscription request and subsequent updates. You can read more about this in the
[GraphQL Ruby guides](https://graphql-ruby.org/subscriptions/subscription_classes).
### Authorization
You should implement the `#authorized?` method of the subscription class so that the initial subscription and subsequent updates are authorized.
When a user is not authorized, you should call the `unauthorized!` helper so that execution is halted and the user is unsubscribed. Returning `false`
results in redaction of the response but we leak information that some updates are happening. This is due to a
[bug in the GraphQL gem](https://github.com/rmosolgo/graphql-ruby/issues/3390).
### Triggering subscriptions
Define a method under the `GraphqlTriggers` module to trigger a subscription. Do not call `GitlabSchema.subscriptions.trigger` directly in application
code so that we have a single source of truth and we do not trigger a subscription with different arguments and objects.
## Pagination implementation
To learn more, visit [GraphQL pagination](graphql_guide/pagination.md).
## Validating arguments
For validations of single arguments, use the
[`prepare` option](https://github.com/rmosolgo/graphql-ruby/blob/master/guides/fields/arguments.md)
as normal.
Sometimes a mutation or resolver may accept a number of optional
arguments, but we still want to validate that at least one of the optional
arguments is provided. In this situation, consider using the `#ready?`
method in your mutation or resolver to provide the validation. The
`#ready?` method is called before any work is done in the
`#resolve` method.
Example:
```ruby
def ready?(**args)
if args.values_at(:body, :position).compact.blank?
raise Gitlab::Graphql::Errors::ArgumentError,
'body or position arguments are required'
end
# Always remember to call `#super`
super
end
```
In the future this may be able to be done using `OneOf Input Objects` if
[this RFC](https://github.com/graphql/graphql-spec/pull/825)
is merged.
## GitLab custom scalars
### `Types::TimeType`
[`Types::TimeType`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app%2Fgraphql%2Ftypes%2Ftime_type.rb)
must be used as the type for all fields and arguments that deal with Ruby
`Time` and `DateTime` objects.
The type is
[a custom scalar](https://github.com/rmosolgo/graphql-ruby/blob/master/guides/type_definitions/scalars.md#custom-scalars)
that:
- Converts Ruby's `Time` and `DateTime` objects into standardized
ISO-8601 formatted strings, when used as the type for our GraphQL fields.
- Converts ISO-8601 formatted time strings into Ruby `Time` objects,
when used as the type for our GraphQL arguments.
This allows our GraphQL API to have a standardized way that it presents time
and handles time inputs.
Example:
```ruby
field :created_at, Types::TimeType, null: true, description: 'Timestamp of when the issue was created.'
```
## Testing
For testing mutations and resolvers, consider the unit of
test a full GraphQL request, not a call to a resolver. The reasons for this are
that we want to avoid lots of coupling to the framework, since this makes
upgrades to dependencies much more difficult.
You should:
- Prefer request specs (either using the full API endpoint or going through
`GitlabSchema.execute`) to unit specs for resolvers and mutations.
- Prefer `GraphqlHelpers#execute_query` and `GraphqlHelpers#run_with_clean_state` to
`GraphqlHelpers#resolve` and `GraphqlHelpers#resolve_field`.
For example:
```ruby
# Good:
gql_query = %q(some query text...)
post_graphql(gql_query, current_user: current_user)
# or:
GitlabSchema.execute(gql_query, context: { current_user: current_user })
# Deprecated: avoid
resolve(described_class, obj: project, ctx: { current_user: current_user })
```
### Writing unit tests (deprecated)
WARNING:
Avoid writing unit tests if the same thing can be tested with
a full GraphQL request.
Before creating unit tests, review the following examples:
- [`spec/graphql/resolvers/users_resolver_spec.rb`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/spec/graphql/resolvers/users_resolver_spec.rb)
- [`spec/graphql/mutations/issues/create_spec.rb`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/spec/graphql/mutations/issues/create_spec.rb)
### Writing integration tests
Integration tests check the full stack for a GraphQL query or mutation and are stored in
`spec/requests/api/graphql`.
For speed, consider calling `GitlabSchema.execute` directly, or making use
of smaller test schemas that only contain the types under test.
However, full request integration tests that check if data is returned verify the following
additional items:
- The mutation is actually queryable in the schema (was mounted in `MutationType`).
- The data returned by a resolver or mutation correctly matches the
[return types](https://graphql-ruby.org/fields/introduction.html#field-return-type) of
the fields and resolves without errors.
- The arguments coerce correctly on input, and the fields serialize correctly
on output.
Integration tests can also verify the following items, because they invoke the
full stack:
- An argument or scalar's [`prepare`](#validating-arguments) applies correctly.
- Logic in a resolver or mutation's [`#ready?` method](#correct-use-of-resolverready) applies correctly.
- An [argument's `default_value`](https://graphql-ruby.org/fields/arguments.html) applies correctly.
- Objects resolve successfully, and there are no N+1 issues.
When adding a query, you can use the `a working graphql query` shared example to test if the query
renders valid results.
You can construct a query including all available fields using the `GraphqlHelpers#all_graphql_fields_for`
helper. This makes it easy to add a test rendering all possible fields for a query.
If you're adding a field to a query that supports pagination and sorting,
visit [Testing](graphql_guide/pagination.md#testing) for details.
To test GraphQL mutation requests, `GraphqlHelpers` provides two
helpers: `graphql_mutation` which takes the name of the mutation, and
a hash with the input for the mutation. This returns a struct with
a mutation query, and prepared variables.
You can then pass this struct to the `post_graphql_mutation` helper,
that posts the request with the correct parameters, like a GraphQL
client would do.
To access the response of a mutation, you can use the `graphql_mutation_response`
helper.
Using these helpers, you can build specs like this:
```ruby
let(:mutation) do
graphql_mutation(
:merge_request_set_wip,
project_path: 'gitlab-org/gitlab-foss',
iid: '1',
wip: true
)
end
it 'returns a successful response' do
post_graphql_mutation(mutation, current_user: user)
expect(response).to have_gitlab_http_status(:success)
expect(graphql_mutation_response(:merge_request_set_wip)['errors']).to be_empty
end
```
### Testing tips and tricks
- Become familiar with the methods in the `GraphqlHelpers` support module.
Many of these methods make writing GraphQL tests easier.
- Use traversal helpers like `GraphqlHelpers#graphql_data_at` and
`GraphqlHelpers#graphql_dig_at` to access result fields. For example:
```ruby
result = GitlabSchema.execute(query)
mr_iid = graphql_dig_at(result.to_h, :data, :project, :merge_request, :iid)
```
- Use `GraphqlHelpers#a_graphql_entity_for` to match against results.
For example:
```ruby
post_graphql(some_query)
# checks that it is a hash containing { id => global_id_of(issue) }
expect(graphql_data_at(:project, :issues, :nodes))
.to contain_exactly(a_graphql_entity_for(issue))
# Additional fields can be passed, either as names of methods, or with values
expect(graphql_data_at(:project, :issues, :nodes))
.to contain_exactly(a_graphql_entity_for(issue, :iid, :title, created_at: some_time))
```
- Use `GraphqlHelpers#empty_schema` to create an empty schema, rather than creating
one by hand. For example:
```ruby
# good
let(:schema) { empty_schema }
# bad
let(:query_type) { GraphQL::ObjectType.new }
let(:schema) { GraphQL::Schema.define(query: query_type, mutation: nil)}
```
- Use `GraphqlHelpers#query_double(schema: nil)` of `double('query', schema: nil)`. For example:
```ruby
# good
let(:query) { query_double(schema: GitlabSchema) }
# bad
let(:query) { double('Query', schema: GitlabSchema) }
```
- Avoid false positives:
Authenticating a user with the `current_user:` argument for `post_graphql`
generates more queries on the first request than on subsequent requests on that
same user. If you are testing for N+1 queries using
[QueryRecorder](query_recorder.md), use a **different** user for each request.
The below example shows how a test for avoiding N+1 queries should look:
```ruby
RSpec.describe 'Query.project(fullPath).pipelines' do
include GraphqlHelpers
let(:project) { create(:project) }
let(:query) do
%(
{
project(fullPath: "#{project.full_path}") {
pipelines {
nodes {
id
}
}
}
}
)
end
it 'avoids N+1 queries' do
first_user = create(:user)
second_user = create(:user)
create(:ci_pipeline, project: project)
control_count = ActiveRecord::QueryRecorder.new do
post_graphql(query, current_user: first_user)
end
create(:ci_pipeline, project: project)
expect do
post_graphql(query, current_user: second_user) # use a different user to avoid a false positive from authentication queries
end.not_to exceed_query_limit(control_count)
end
end
```
- Mimic the folder structure of `app/graphql/types`:
For example, tests for fields on `Types::Ci::PipelineType`
in `app/graphql/types/ci/pipeline_type.rb` should be stored in
`spec/requests/api/graphql/ci/pipeline_spec.rb` regardless of the query being
used to fetch the pipeline data.
- There can be possible cyclic dependencies within our GraphQL types.
See [Adding field with resolver on a Type causes "Can't determine the return type " error on a different Type](https://github.com/rmosolgo/graphql-ruby/issues/3974#issuecomment-1084444214)
and [Fix unresolved name due to cyclic definition](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/84202/diffs#diff-content-32d14251082fd45412e1fdbf5820e62d157e70d2).
In particular, this can happen with `connection_type`. Normally we might use the following in a resolver:
```ruby
type Types::IssueType.connection_type, null: true
```
However this might cause a cyclic definition, which can result in errors like:
```ruby
NameError: uninitialized constant Resolvers::GroupIssuesResolver
```
To fix this, we must create a new file that encapsulates the connection type,
and then reference it using double quotes. This gives a delayed resolution,
and the proper connection type. For example:
```ruby
module Types
# rubocop: disable Graphql/AuthorizeTypes
class IssueConnectionType < CountableConnectionType
end
end
Types::IssueConnectionType.prepend_mod_with('Types::IssueConnectionType')
```
in [types/issue_connection_type.rb](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/graphql/types/issue_connection_type.rb)
defines a new `Types::IssueConnectionType`, and is then referenced in
[app/graphql/resolvers/base_issues_resolver.rb](https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/graphql/resolvers/base_issues_resolver.rb)
```ruby
type "Types::IssueConnection", null: true
```
Only use this style if you are having spec failures. This is not intended to be a new
pattern that we use. This issue may disappear after we've upgraded to `2.x`.
- There can be instances where a spec fails because the class is not loaded correctly.
It relates to the
[circular dependencies problem](https://github.com/rmosolgo/graphql-ruby/issues/1929) and
[Adding field with resolver on a Type causes "Can't determine the return type " error on a different Type](https://github.com/rmosolgo/graphql-ruby/issues/3974).
Unfortunately, the errors generated don't really indicate what the problem is. For example,
remove the quotes from the `Rspec.descrbe` in
[ee/spec/graphql/resolvers/compliance_management/merge_requests/compliance_violation_resolver_spec.rb](https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/spec/graphql/resolvers/compliance_management/merge_requests/compliance_violation_resolver_spec.rb).
Then run `rspec ee/spec/graphql/resolvers/compliance_management/merge_requests/compliance_violation_resolver_spec.rb`.
This generates errors with the expectations. For example:
```ruby
1) Resolvers::ComplianceManagement::MergeRequests::ComplianceViolationResolver#resolve user is authorized filtering the results when given an array of project IDs finds the filtered compliance violations
Failure/Error: expect(subject).to contain_exactly(compliance_violation)
expected collection contained: [#<MergeRequests::ComplianceViolation id: 4, violating_user_id: 26, merge_request_id: 4, reason: "approved_by_committer", severity_level: "low">]
actual collection contained: [#<MergeRequests::ComplianceViolation id: 4, violating_user_id: 26, merge_request_id: 4, reason: "app...er_id: 27, merge_request_id: 5, reason: "approved_by_merge_request_author", severity_level: "high">]
the extra elements were: [#<MergeRequests::ComplianceViolation id: 5, violating_user_id: 27, merge_request_id: 5, reason: "approved_by_merge_request_author", severity_level: "high">]
# ./ee/spec/graphql/resolvers/compliance_management/merge_requests/compliance_violation_resolver_spec.rb:55:in `block (6 levels) in <top (required)>'
```
However, this is not a case of the wrong result being generated, it's because of the loading order
of the `ComplianceViolationResolver` class.
The only way we've found to fix this is by quoting the class name in the spec. For example, changing
```ruby
RSpec.describe Resolvers::ComplianceManagement::MergeRequests::ComplianceViolationResolver do
```
into:
```ruby
RSpec.describe 'Resolvers::ComplianceManagement::MergeRequests::ComplianceViolationResolver' do
```
See [this merge request](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/87295#note_946174036) for some discussion.
Only use this style if you are having spec failures. This is not intended to be a new
pattern that we use. This issue may disappear after we've upgraded to `2.x`.
- When testing resolvers using `GraphqlHelpers#resolve`, arguments for the resolver can be handled two ways.
1. 95% of the resolver specs use arguments that are Ruby objects, as opposed to when using the GraphQL API
only strings and integers are used. This works fine in most cases.
1. If your resolver takes arguments that use a `prepare` proc, such as a resolver that accepts timeframe
arguments (`TimeFrameArguments`), you must pass the `arg_style: :internal_prepared` parameter into
the `resolve` method. This tells the code to convert the arguments into strings and integers and pass
them through regular argument handling, ensuring that the `prepare` proc is called correctly.
For example in [`iterations_resolver_spec.rb`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/spec/graphql/resolvers/iterations_resolver_spec.rb):
```ruby
def resolve_group_iterations(args = {}, obj = group, context = { current_user: current_user })
resolve(described_class, obj: obj, args: args, ctx: context, arg_style: :internal_prepared)
end
```
One additional caveat is that if you are passing enums as a resolver argument, you must use the
external representation of the enum, rather than the internal. For example:
```ruby
# good
resolve_group_iterations({ search: search, in: ['CADENCE_TITLE'] })
# bad
resolve_group_iterations({ search: search, in: [:cadence_title] })
```
The use of `:internal_prepared` was added as a bridge for the
[GraphQL gem](https://graphql-ruby.org) upgrade. Testing resolvers directly will be
[removed eventually](https://gitlab.com/gitlab-org/gitlab/-/issues/363121),
and writing unit tests for resolvers/mutations is
[already deprecated](#writing-unit-tests-deprecated)
## Notes about Query flow and GraphQL infrastructure
The GitLab GraphQL infrastructure can be found in `lib/gitlab/graphql`.
[Instrumentation](https://graphql-ruby.org/queries/instrumentation.html) is functionality
that wraps around a query being executed. It is implemented as a module that uses the `Instrumentation` class.
Example: `Present`
```ruby
module Gitlab
module Graphql
module Present
#... some code above...
def self.use(schema_definition)
schema_definition.instrument(:field, ::Gitlab::Graphql::Present::Instrumentation.new)
end
end
end
end
```
A [Query Analyzer](https://graphql-ruby.org/queries/ast_analysis.html#analyzer-api) contains a series
of callbacks to validate queries before they are executed. Each field can pass through
the analyzer, and the final value is also available to you.
[Multiplex queries](https://graphql-ruby.org/queries/multiplex.html) enable
multiple queries to be sent in a single request. This reduces the number of requests sent to the server.
(there are custom Multiplex Query Analyzers and Multiplex Instrumentation provided by GraphQL Ruby).
### Query limits
Queries and mutations are limited by depth, complexity, and recursion
to protect server resources from overly ambitious or malicious queries.
These values can be set as defaults and overridden in specific queries as needed.
The complexity values can be set per object as well, and the final query complexity is
evaluated based on how many objects are being returned. This is useful
for objects that are expensive (such as requiring Gitaly calls).
For example, a conditional complexity method in a resolver:
```ruby
def self.resolver_complexity(args, child_complexity:)
complexity = super
complexity += 2 if args[:labelName]
complexity
end
```
More about complexity:
[GraphQL Ruby documentation](https://graphql-ruby.org/queries/complexity_and_depth.html).
## Documentation and schema
Our schema is located at `app/graphql/gitlab_schema.rb`.
See the [schema reference](../api/graphql/reference/index.md) for details.
This generated GraphQL documentation needs to be updated when the schema changes.
For information on generating GraphQL documentation and schema files, see
[updating the schema documentation](rake_tasks.md#update-graphql-documentation-and-schema-definitions).
To help our readers, you should also add a new page to our [GraphQL API](../api/graphql/index.md) documentation.
For guidance, see the [GraphQL API](documentation/graphql_styleguide.md) page.
## Include a changelog entry
All client-facing changes **must** include a [changelog entry](changelog.md).
## Laziness
One important technique unique to GraphQL for managing performance is
using **lazy** values. Lazy values represent the promise of a result,
allowing their action to be run later, which enables batching of queries in
different parts of the query tree. The main example of lazy values in our code is
the [GraphQL BatchLoader](graphql_guide/batchloader.md).
To manage lazy values directly, read `Gitlab::Graphql::Lazy`, and in
particular `Gitlab::Graphql::Laziness`. This contains `#force` and
`#delay`, which help implement the basic operations of creation and
elimination of laziness, where needed.
For dealing with lazy values without forcing them, use
`Gitlab::Graphql::Lazy.with_value`.
## Monitoring GraphQL
See the [Monitoring GraphQL](graphql_guide/monitoring.md) guide for tips on how to inspect logs of GraphQL requests and monitor the performance of your GraphQL queries.
|