Swap FK external_pull_requests to projects for LFK

Swaps FK for external_pull_requests.project_id to projects

Changelog: changed

db/post_migrate/20220124145019_remove_projects_external_pull_requests_project_id_fk.rb

+# frozen_string_literal: true
+
+class RemoveProjectsExternalPullRequestsProjectIdFk < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  def up
+    return unless foreign_key_exists?(:external_pull_requests, :projects, name: "fk_rails_bcae9b5c7b")
+
+    with_lock_retries do
+      execute('LOCK projects, external_pull_requests IN ACCESS EXCLUSIVE MODE') if transaction_open?
+
+      remove_foreign_key_if_exists(:external_pull_requests, :projects, name: "fk_rails_bcae9b5c7b")
+    end
+  end
+
+  def down
+    add_concurrent_foreign_key(:external_pull_requests, :projects, name: "fk_rails_bcae9b5c7b", column: :project_id, target_column: :id, on_delete: :cascade)
+  end
+end

db/schema_migrations/20220124145019

+3b1f7a7b6481a960ac25523e5e1b5abc6c1436332d64d4319d9e4112b0fa765e
\ No newline at end of file

db/structure.sql

@@ -31166,9 +31166,6 @@ ALTER TABLE ONLY projects_sync_events
 ALTER TABLE ONLY approval_merge_request_rules_users
     ADD CONSTRAINT fk_rails_bc8972fa55 FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;
 
-ALTER TABLE ONLY external_pull_requests
-    ADD CONSTRAINT fk_rails_bcae9b5c7b FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE;
-
 ALTER TABLE ONLY elasticsearch_indexed_projects
     ADD CONSTRAINT fk_rails_bd13bbdc3d FOREIGN KEY (project_id) REFERENCES projects(id) ON DELETE CASCADE;
 

lib/gitlab/database/gitlab_loose_foreign_keys.yml

@@ -38,6 +38,10 @@ ci_daily_build_group_report_results:
   - table: projects
     column: project_id
     on_delete: async_delete
+external_pull_requests:
+  - table: projects
+    column: project_id
+    on_delete: async_delete
 ci_freeze_periods:
   - table: projects
     column: project_id

spec/lib/gitlab/database/no_cross_db_foreign_keys_spec.rb

@@ -42,7 +42,6 @@ RSpec.describe 'cross-database foreign keys' do
       ci_unit_tests.project_id
       ci_variables.project_id
       dast_site_profiles_pipelines.ci_pipeline_id
-      external_pull_requests.project_id
       vulnerability_feedback.pipeline_id
     ).freeze
   end

spec/models/external_pull_request_spec.rb

@@ -236,4 +236,11 @@ RSpec.describe ExternalPullRequest do
   it_behaves_like 'it has loose foreign keys' do
     let(:factory_name) { :external_pull_request }
   end
+
+  context 'loose foreign key on external_pull_requests.project_id' do
+    it_behaves_like 'cleanup by a loose foreign key' do
+      let!(:parent) { create(:project) }
+      let!(:model) { create(:external_pull_request, project: parent) }
+    end
+  end
 end