Add a column linking an MR to its diff

We already had this the other way around (merge_request_diffs.merge_request_id),
but this is needed to gather only the most recent diffs for a set of merge
requests.

3 files changed, 57 insertions, 1 deletions

diff --git a/db/migrate/20171025110159_add_latest_merge_request_diff_id_to_merge_requests.rb b/db/migrate/20171025110159_add_latest_merge_request_diff_id_to_merge_requests.rb
new file mode 100644
index 00000000000..74a2badc130
--- /dev/null
+++ b/db/migrate/20171025110159_add_latest_merge_request_diff_id_to_merge_requests.rb
@@ -0,0 +1,26 @@
+class AddLatestMergeRequestDiffIdToMergeRequests < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_column :merge_requests, :latest_merge_request_diff_id, :integer
+    add_concurrent_index :merge_requests, :latest_merge_request_diff_id
+
+    add_concurrent_foreign_key :merge_requests, :merge_request_diffs,
+                               column: :latest_merge_request_diff_id,
+                               on_delete: :nullify
+  end
+
+  def down
+    remove_foreign_key :merge_requests, column: :latest_merge_request_diff_id
+
+    if index_exists?(:merge_requests, :latest_merge_request_diff_id)
+      remove_concurrent_index :merge_requests, :latest_merge_request_diff_id
+    end
+
+    remove_column :merge_requests, :latest_merge_request_diff_id
+  end
+end
diff --git a/db/post_migrate/20171026082505_populate_merge_requests_latest_merge_request_diff_id.rb b/db/post_migrate/20171026082505_populate_merge_requests_latest_merge_request_diff_id.rb
new file mode 100644
index 00000000000..a7ebbbf34c0
--- /dev/null
+++ b/db/post_migrate/20171026082505_populate_merge_requests_latest_merge_request_diff_id.rb
@@ -0,0 +1,27 @@
+class PopulateMergeRequestsLatestMergeRequestDiffId < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  BATCH_SIZE = 1_000
+
+  class MergeRequest < ActiveRecord::Base
+    self.table_name = 'merge_requests'
+
+    include ::EachBatch
+  end
+
+  disable_ddl_transaction!
+
+  def up
+    update = '
+      latest_merge_request_diff_id = (
+        SELECT MAX(id)
+        FROM merge_request_diffs
+        WHERE merge_requests.id = merge_request_diffs.merge_request_id
+      )'.squish
+
+    MergeRequest.where(latest_merge_request_diff_id: nil).each_batch(of: BATCH_SIZE) do |relation|
+      relation.update_all(update)
+    end
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 530f08022be..6e23f17d393 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20171017145932) do
+ActiveRecord::Schema.define(version: 20171026082505) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -973,6 +973,7 @@ ActiveRecord::Schema.define(version: 20171017145932) do
     t.boolean "ref_fetched"
     t.string "merge_jid"
     t.boolean "discussion_locked"
+    t.integer "latest_merge_request_diff_id"
   end
 
   add_index "merge_requests", ["assignee_id"], name: "index_merge_requests_on_assignee_id", using: :btree
@@ -981,6 +982,7 @@ ActiveRecord::Schema.define(version: 20171017145932) do
   add_index "merge_requests", ["deleted_at"], name: "index_merge_requests_on_deleted_at", using: :btree
   add_index "merge_requests", ["description"], name: "index_merge_requests_on_description_trigram", using: :gin, opclasses: {"description"=>"gin_trgm_ops"}
   add_index "merge_requests", ["head_pipeline_id"], name: "index_merge_requests_on_head_pipeline_id", using: :btree
+  add_index "merge_requests", ["latest_merge_request_diff_id"], name: "index_merge_requests_on_latest_merge_request_diff_id", using: :btree
   add_index "merge_requests", ["milestone_id"], name: "index_merge_requests_on_milestone_id", using: :btree
   add_index "merge_requests", ["source_branch"], name: "index_merge_requests_on_source_branch", using: :btree
   add_index "merge_requests", ["source_project_id", "source_branch"], name: "index_merge_requests_on_source_project_id_and_source_branch", using: :btree
@@ -1846,6 +1848,7 @@ ActiveRecord::Schema.define(version: 20171017145932) do
   add_foreign_key "merge_request_metrics", "ci_pipelines", column: "pipeline_id", on_delete: :cascade
   add_foreign_key "merge_request_metrics", "merge_requests", on_delete: :cascade
   add_foreign_key "merge_requests", "ci_pipelines", column: "head_pipeline_id", name: "fk_fd82eae0b9", on_delete: :nullify
+  add_foreign_key "merge_requests", "merge_request_diffs", column: "latest_merge_request_diff_id", name: "fk_06067f5644", on_delete: :nullify
   add_foreign_key "merge_requests", "projects", column: "target_project_id", name: "fk_a6963e8447", on_delete: :cascade
   add_foreign_key "merge_requests_closing_issues", "issues", on_delete: :cascade
   add_foreign_key "merge_requests_closing_issues", "merge_requests", on_delete: :cascade