1 files changed, 43 insertions, 0 deletions
diff --git a/db/migrate/20171114150259_merge_requests_author_id_foreign_key.rb b/db/migrate/20171114150259_merge_requests_author_id_foreign_key.rb
new file mode 100644
index 00000000000..021eaa04a0c
--- /dev/null
+++ b/db/migrate/20171114150259_merge_requests_author_id_foreign_key.rb
@@ -0,0 +1,43 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class MergeRequestsAuthorIdForeignKey < 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_authors
+      where('NOT EXISTS (SELECT true FROM users WHERE merge_requests.author_id = users.id)')
+        .where('author_id IS NOT NULL')
+    end
+  end
+
+  def up
+    # Replacing the ghost user ID logic would be too complex, hence we don't
+    # redefine the User model here.
+    ghost_id = User.select(:id).ghost.id
+
+    MergeRequest.with_orphaned_authors.each_batch(of: 100) do |batch|
+      batch.update_all(author_id: ghost_id)
+    end
+
+    add_concurrent_foreign_key(
+      :merge_requests,
+      :users,
+      column: :author_id,
+      on_delete: :nullify
+    )
+  end
+
+  def down
+    remove_foreign_key(:merge_requests, column: :author_id)
+  end
+end