Add FK for deployments.environment_id to environments table

This commit adds the foreign key for the environment_id
column, which is long overdue.

Changelog: other

db/migrate/20210622135221_add_foreign_key_for_environment_id_to_environments.rb

+# frozen_string_literal: true
+
+class AddForeignKeyForEnvironmentIdToEnvironments < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  disable_ddl_transaction!
+
+  def up
+    # `validate: false` option is passed here, because validating the existing rows fails by the orphaned deployments,
+    # which will be cleaned up in https://gitlab.com/gitlab-org/gitlab/-/merge_requests/64588.
+    # The validation runs for only new records or updates, so that we can at least
+    # stop creating orphaned rows.
+    add_concurrent_foreign_key :deployments, :environments, column: :environment_id, on_delete: :cascade, validate: false
+  end
+
+  def down
+    with_lock_retries do
+      remove_foreign_key_if_exists :deployments, :environments
+    end
+  end
+end

db/schema_migrations/20210622135221

+e43889baa57ea2cd0b87ba98819408115955f6a6586b3275cf0a08bd79909c71
\ No newline at end of file

db/structure.sql

@@ -25507,6 +25507,9 @@ CREATE TRIGGER trigger_has_external_wiki_on_update AFTER UPDATE ON services FOR
 ALTER TABLE ONLY chat_names
     ADD CONSTRAINT fk_00797a2bf9 FOREIGN KEY (service_id) REFERENCES services(id) ON DELETE CASCADE;
 
+ALTER TABLE ONLY deployments
+    ADD CONSTRAINT fk_009fd21147 FOREIGN KEY (environment_id) REFERENCES environments(id) ON DELETE CASCADE NOT VALID;
+
 ALTER TABLE ONLY epics
     ADD CONSTRAINT fk_013c9f36ca FOREIGN KEY (due_date_sourcing_epic_id) REFERENCES epics(id) ON DELETE SET NULL;
 

spec/db/schema_spec.rb

@@ -34,7 +34,7 @@ RSpec.describe 'Database schema' do
     compliance_management_frameworks: %w[group_id],
     commit_user_mentions: %w[commit_id],
     deploy_keys_projects: %w[deploy_key_id],
-    deployments: %w[deployable_id environment_id user_id],
+    deployments: %w[deployable_id user_id],
     draft_notes: %w[discussion_id commit_id],
     epics: %w[updated_by_id last_edited_by_id state_id],
     events: %w[target_id],