Add a column linking an MR to its diff

We already had this the other way around (merge_request_diffs.merge_request_id),
but this is needed to gather only the most recent diffs for a set of merge
requests.

1 files changed, 26 insertions, 0 deletions

diff --git a/db/migrate/20171025110159_add_latest_merge_request_diff_id_to_merge_requests.rb b/db/migrate/20171025110159_add_latest_merge_request_diff_id_to_merge_requests.rb
new file mode 100644
index 00000000000..74a2badc130
--- /dev/null
+++ b/db/migrate/20171025110159_add_latest_merge_request_diff_id_to_merge_requests.rb
@@ -0,0 +1,26 @@
+class AddLatestMergeRequestDiffIdToMergeRequests < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_column :merge_requests, :latest_merge_request_diff_id, :integer
+    add_concurrent_index :merge_requests, :latest_merge_request_diff_id
+
+    add_concurrent_foreign_key :merge_requests, :merge_request_diffs,
+                               column: :latest_merge_request_diff_id,
+                               on_delete: :nullify
+  end
+
+  def down
+    remove_foreign_key :merge_requests, column: :latest_merge_request_diff_id
+
+    if index_exists?(:merge_requests, :latest_merge_request_diff_id)
+      remove_concurrent_index :merge_requests, :latest_merge_request_diff_id
+    end
+
+    remove_column :merge_requests, :latest_merge_request_diff_id
+  end
+end