Add ON DELETE constraint to namespace_id FK on gitlab_subscriptions

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20181212104941) do
+ActiveRecord::Schema.define(version: 20181215161939) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -3260,7 +3260,7 @@ ActiveRecord::Schema.define(version: 20181212104941) do
   add_foreign_key "geo_repository_renamed_events", "projects", on_delete: :cascade
   add_foreign_key "geo_repository_updated_events", "projects", on_delete: :cascade
   add_foreign_key "geo_reset_checksum_events", "projects", on_delete: :cascade
-  add_foreign_key "gitlab_subscriptions", "namespaces"
+  add_foreign_key "gitlab_subscriptions", "namespaces", name: "fk_e2595d00a1", on_delete: :cascade
   add_foreign_key "gitlab_subscriptions", "plans", column: "hosted_plan_id", name: "fk_bd0c4019c3", on_delete: :cascade
   add_foreign_key "gpg_key_subkeys", "gpg_keys", on_delete: :cascade
   add_foreign_key "gpg_keys", "users", on_delete: :cascade

ee/db/migrate/20181215161939_add_on_delete_cascade_to_namespace_id_fk_on_gitlab_subscriptions.rb

+# frozen_string_literal: true
+
+class AddOnDeleteCascadeToNamespaceIdFkOnGitlabSubscriptions < ActiveRecord::Migration[5.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    remove_foreign_key(:gitlab_subscriptions, column: :namespace_id)
+
+    add_concurrent_foreign_key(:gitlab_subscriptions, :namespaces, column: :namespace_id)
+  end
+
+  def down
+    # Previously there was a foreign key without a CASCADING DELETE, so we'll
+    # just leave the foreign key in place.
+  end
+end