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Diffstat (limited to 'doc/development/foreign_keys.md')
| -rw-r--r-- | doc/development/foreign_keys.md | 24 |
1 files changed, 12 insertions, 12 deletions
diff --git a/doc/development/foreign_keys.md b/doc/development/foreign_keys.md index c20c70623ae..77df6fbfb0d 100644 --- a/doc/development/foreign_keys.md +++ b/doc/development/foreign_keys.md @@ -1,5 +1,5 @@ --- -stage: Enablement +stage: Data Stores group: Database info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments --- @@ -15,7 +15,7 @@ class User < ActiveRecord::Base end ``` -Here you will need to add a foreign key on column `posts.user_id`. This ensures +Add a foreign key here on column `posts.user_id`. This ensures that data consistency is enforced on database level. Foreign keys also mean that the database can very quickly remove associated data (for example, when removing a user), instead of Rails having to do this. @@ -28,7 +28,7 @@ Guide](migration_style_guide.md) for more information. Keep in mind that you can only safely add foreign keys to existing tables after you have removed any orphaned rows. The method `add_concurrent_foreign_key` -does not take care of this so you'll need to do so manually. See +does not take care of this so you need to do so manually. See [adding foreign key constraint to an existing column](database/add_foreign_key_to_existing_column.md). ## Cascading Deletes @@ -39,7 +39,7 @@ this should be set to `CASCADE`. ## Indexes When adding a foreign key in PostgreSQL the column is not indexed automatically, -thus you must also add a concurrent index. Not doing so will result in cascading +thus you must also add a concurrent index. Not doing so results in cascading deletes being very slow. ## Naming foreign keys @@ -48,7 +48,7 @@ By default Ruby on Rails uses the `_id` suffix for foreign keys. So we should only use this suffix for associations between two tables. If you want to reference an ID on a third party platform the `_xid` suffix is recommended. -The spec `spec/db/schema_spec.rb` will test if all columns with the `_id` suffix +The spec `spec/db/schema_spec.rb` tests if all columns with the `_id` suffix have a foreign key constraint. So if that spec fails, don't add the column to `IGNORED_FK_COLUMNS`, but instead add the FK constraint, or consider naming it differently. @@ -56,7 +56,7 @@ differently. ## Dependent Removals Don't define options such as `dependent: :destroy` or `dependent: :delete` when -defining an association. Defining these options means Rails will handle the +defining an association. Defining these options means Rails handles the removal of data, instead of letting the database handle this in the most efficient way possible. @@ -80,13 +80,13 @@ foreign keys to remove the data as this would result in the file system data being left behind. In such a case you should use a service class instead that takes care of removing non database data. -In cases where the relation spans multiple databases you will have even +In cases where the relation spans multiple databases you have even further problems using `dependent: :destroy` or the above hooks. You can read more about alternatives at [Avoid `dependent: :nullify` and `dependent: :destroy` across databases](database/multiple_databases.md#avoid-dependent-nullify-and-dependent-destroy-across-databases). -## Alternative primary keys with has_one associations +## Alternative primary keys with `has_one` associations Sometimes a `has_one` association is used to create a one-to-one relationship: @@ -112,9 +112,9 @@ create_table :user_configs, id: false do |t| end ``` -Setting `default: nil` will ensure a primary key sequence is not created, and since the primary key -will automatically get an index, we set `index: false` to avoid creating a duplicate. -You will also need to add the new primary key to the model: +Setting `default: nil` ensures a primary key sequence is not created, and since the primary key +automatically gets an index, we set `index: false` to avoid creating a duplicate. +You also need to add the new primary key to the model: ```ruby class UserConfig < ActiveRecord::Base @@ -126,4 +126,4 @@ end Using a foreign key as primary key saves space but can make [batch counting](service_ping/implement.md#batch-counters) in [Service Ping](service_ping/index.md) less efficient. -Consider using a regular `id` column if the table will be relevant for Service Ping. +Consider using a regular `id` column if the table is relevant for Service Ping. |