User emails dependent destroy to foreign key cascade delete

The user emails relationship still relied on the Rails
dependent destroy mechanism. This change moves that dependent
destroy to a proper foreign key with cascading delete.

app/models/user.rb

@@ -107,7 +107,7 @@ class User < ApplicationRecord
   has_many :group_deploy_keys
   has_many :gpg_keys
 
-  has_many :emails, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
+  has_many :emails
   has_many :personal_access_tokens, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
   has_many :identities, dependent: :destroy, autosave: true # rubocop:disable Cop/ActiveRecordDependent
   has_many :u2f_registrations, dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent

changelogs/unreleased/dblessing-emails-cascade-delete.yml

+---
+title: Add emails user_id foreign key with cascade delete
+merge_request: 39899
+author:
+type: other

db/migrate/20200819192143_add_emails_user_id_foreign_key.rb

+# frozen_string_literal: true
+
+class AddEmailsUserIdForeignKey < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  CONSTRAINT_NAME = 'fk_emails_user_id'
+
+  def up
+    with_lock_retries do
+      add_foreign_key :emails, :users, on_delete: :cascade, validate: false, name: CONSTRAINT_NAME
+    end
+  end
+
+  def down
+    with_lock_retries do
+      remove_foreign_key_if_exists :emails, column: :user_id, name: CONSTRAINT_NAME
+    end
+  end
+end

db/post_migrate/20200819202048_remove_orphaned_emails.rb

+# frozen_string_literal: true
+
+class RemoveOrphanedEmails < ActiveRecord::Migration[6.0]
+  DOWNTIME = false
+
+  def up
+    execute <<~SQL
+      DELETE FROM emails
+        WHERE not exists (
+          SELECT 1 FROM users WHERE users.id = emails.user_id
+        );
+    SQL
+
+    execute 'DELETE FROM emails WHERE user_id IS NULL;'
+  end
+
+  def down
+    # no-op
+  end
+end

db/post_migrate/20200819202222_validate_emails_user_id_foreign_key.rb

+# frozen_string_literal: true
+
+class ValidateEmailsUserIdForeignKey < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  CONSTRAINT_NAME = 'fk_emails_user_id'
+
+  def up
+    validate_foreign_key :emails, :user_id, name: CONSTRAINT_NAME
+  end
+
+  def down
+    # no op
+  end
+end

db/schema_migrations/20200819192143

+5a5278fdd9539d33a6de226a84ed39b7c5a26929cec68ec5e8d193afb3cfafa2
\ No newline at end of file

db/schema_migrations/20200819202048

+476bce9b18177f37b31e15d42f5a1391c0bfbbd312a513c1d5b43085b90afb3e
\ No newline at end of file

db/schema_migrations/20200819202222

+5e2dfdf725ad0a3d90b240ced74cf5a872f7126b716847f9f9e99b4ad2a22109
\ No newline at end of file

db/structure.sql

@@ -21965,6 +21965,9 @@ ALTER TABLE ONLY public.events
 ALTER TABLE ONLY public.vulnerabilities
     ADD CONSTRAINT fk_efb96ab1e2 FOREIGN KEY (project_id) REFERENCES public.projects(id) ON DELETE CASCADE;
 
+ALTER TABLE ONLY public.emails
+    ADD CONSTRAINT fk_emails_user_id FOREIGN KEY (user_id) REFERENCES public.users(id) ON DELETE CASCADE;
+
 ALTER TABLE ONLY public.clusters
     ADD CONSTRAINT fk_f05c5e5a42 FOREIGN KEY (management_project_id) REFERENCES public.projects(id) ON DELETE SET NULL;
 

spec/db/schema_spec.rb

@@ -35,7 +35,6 @@ RSpec.describe 'Database schema' do
     deploy_keys_projects: %w[deploy_key_id],
     deployments: %w[deployable_id environment_id user_id],
     draft_notes: %w[discussion_id commit_id],
-    emails: %w[user_id],
     epics: %w[updated_by_id last_edited_by_id state_id],
     events: %w[target_id],
     forked_project_links: %w[forked_from_project_id],