1 files changed, 45 insertions, 0 deletions
diff --git a/db/migrate/20171114161914_merge_requests_source_project_id_foreign_key.rb b/db/migrate/20171114161914_merge_requests_source_project_id_foreign_key.rb
new file mode 100644
index 00000000000..2965e580c84
--- /dev/null
+++ b/db/migrate/20171114161914_merge_requests_source_project_id_foreign_key.rb
@@ -0,0 +1,45 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class MergeRequestsSourceProjectIdForeignKey < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  class MergeRequest < ActiveRecord::Base
+    include EachBatch
+
+    self.table_name = 'merge_requests'
+
+    def self.with_orphaned_source_projects
+      where('NOT EXISTS (SELECT true FROM projects WHERE merge_requests.source_project_id = projects.id)')
+        .where('source_project_id IS NOT NULL')
+    end
+  end
+
+  def up
+    MergeRequest.with_orphaned_source_projects.each_batch(of: 100) do |batch|
+      batch.update_all(source_project_id: nil)
+    end
+
+    # We need to allow NULL values so we can nullify the column when the source
+    # project is removed. We _don't_ want to remove the merge request, instead
+    # the application will keep them but close them.
+    change_column_null(:merge_requests, :source_project_id, true)
+
+    add_concurrent_foreign_key(
+      :merge_requests,
+      :projects,
+      column: :source_project_id,
+      on_delete: :nullify
+    )
+  end
+
+  def down
+    remove_foreign_key_without_error(:merge_requests, column: :source_project_id)
+    change_column_null(:merge_requests, :source_project_id, false)
+  end
+end