Allow custom names for concurrent foreign keys

This is necessary for backporting the EE schema to ensure backported
foreign keys use the same key names.

lib/gitlab/database/migration_helpers.rb

@@ -149,7 +149,7 @@ module Gitlab
       # column - The name of the column to create the foreign key on.
       # on_delete - The action to perform when associated data is removed,
       #             defaults to "CASCADE".
-      def add_concurrent_foreign_key(source, target, column:, on_delete: :cascade)
+      def add_concurrent_foreign_key(source, target, column:, on_delete: :cascade, name: nil)
         # Transactions would result in ALTER TABLE locks being held for the
         # duration of the transaction, defeating the purpose of this method.
         if transaction_open?
@@ -167,14 +167,18 @@ module Gitlab
             return
           end
-          return add_foreign_key(source, target,
-                                 column: column,
-                                 on_delete: on_delete)
+          key_options = { column: column, on_delete: on_delete }
+
+          # The MySQL adapter tries to create a foreign key without a name when
+          # `:name` is nil, instead of generating a name for us.
+          key_options[:name] = name if name
+
+          return add_foreign_key(source, target, key_options)
         else
           on_delete = 'SET NULL' if on_delete == :nullify
         end
-        key_name = concurrent_foreign_key_name(source, column)
+        key_name = name || concurrent_foreign_key_name(source, column)
         unless foreign_key_exists?(source, target, column: column)
           Rails.logger.warn "Foreign key not created because it exists already " \

spec/lib/gitlab/database/migration_helpers_spec.rb

@@ -214,6 +214,23 @@ describe Gitlab::Database::MigrationHelpers do
           model.add_concurrent_foreign_key(:projects, :users, column: :user_id)
         end
+        it 'allows the use of a custom key name' do
+          expect(model).to receive(:add_foreign_key).with(
+            :projects,
+            :users,
+            column: :user_id,
+            on_delete: :cascade,
+            name: :foo
+          )
+
+          model.add_concurrent_foreign_key(
+            :projects,
+            :users,
+            column: :user_id,
+            name: :foo
+          )
+        end
+
         it 'does not create a foreign key if it exists already' do
           expect(model).to receive(:foreign_key_exists?).with(:projects, :users, column: :user_id).and_return(true)
           expect(model).not_to receive(:add_foreign_key)
@@ -257,6 +274,16 @@ describe Gitlab::Database::MigrationHelpers do
           model.add_concurrent_foreign_key(:projects, :users, column: :user_id)
         end
+
+        it 'allows the use of a custom key name' do
+          expect(model).to receive(:disable_statement_timeout).and_call_original
+          expect(model).to receive(:execute).with(/statement_timeout/)
+          expect(model).to receive(:execute).ordered.with(/NOT VALID/)
+          expect(model).to receive(:execute).ordered.with(/VALIDATE CONSTRAINT.+foo/)
+          expect(model).to receive(:execute).with(/RESET ALL/)
+
+          model.add_concurrent_foreign_key(:projects, :users, column: :user_id, name: :foo)
+        end
       end
     end
   end