Cache merged and closed events data in merge_request_metrics table

3 files changed, 35 insertions, 7 deletions

diff --git a/app/serializers/event_entity.rb b/app/serializers/event_entity.rb
deleted file mode 100644
index 935d67a4f37..00000000000
--- a/app/serializers/event_entity.rb
+++ /dev/null
@@ -1,4 +0,0 @@
-class EventEntity < Grape::Entity
-  expose :author, using: UserEntity
-  expose :updated_at
-end
diff --git a/app/serializers/merge_request_metrics_entity.rb b/app/serializers/merge_request_metrics_entity.rb
new file mode 100644
index 00000000000..3548107ac16
--- /dev/null
+++ b/app/serializers/merge_request_metrics_entity.rb
@@ -0,0 +1,6 @@
+class MergeRequestMetricsEntity < Grape::Entity
+  expose :latest_closed_at, as: :closed_at
+  expose :merged_at
+  expose :latest_closed_by, as: :closed_by, using: UserEntity
+  expose :merged_by, using: UserEntity
+end
diff --git a/app/serializers/merge_request_widget_entity.rb b/app/serializers/merge_request_widget_entity.rb
index f8e59b2ffd7..83ea36adcc1 100644
--- a/app/serializers/merge_request_widget_entity.rb
+++ b/app/serializers/merge_request_widget_entity.rb
@@ -17,9 +17,11 @@ class MergeRequestWidgetEntity < IssuableEntity
     merge_request.project.merge_requests_ff_only_enabled
   end
 
-  # Events
-  expose :merge_event, using: EventEntity
-  expose :closed_event, using: EventEntity
+  expose :metrics do |merge_request|
+    metrics = build_metrics(merge_request)
+
+    MergeRequestMetricsEntity.new(metrics).as_json
+  end
 
   # User entities
   expose :merge_user, using: UserEntity
@@ -178,4 +180,28 @@ class MergeRequestWidgetEntity < IssuableEntity
     @presenters ||= {}
     @presenters[merge_request] ||= MergeRequestPresenter.new(merge_request, current_user: current_user)
   end
+
+  # Once SchedulePopulateMergeRequestMetricsWithEventsData fully runs,
+  # we can remove this method and just serialize MergeRequest#metrics
+  # instead. See https://gitlab.com/gitlab-org/gitlab-ce/issues/41587
+  def build_metrics(merge_request)
+    # There's no need to query and serialize metrics data for merge requests that are not
+    # merged or closed.
+    case merge_request.state
+    when 'merged'
+      merge_request.metrics&.merged_by_id ? merge_request.metrics : build_metrics_from_events(merge_request)
+    when 'closed'
+      merge_request.metrics&.latest_closed_by_id ? merge_request.metrics : build_metrics_from_events(merge_request)
+    end
+  end
+
+  def build_metrics_from_events(merge_request)
+    closed_event = merge_request.closed_event
+    merge_event = merge_request.merge_event
+
+    MergeRequest::Metrics.new(latest_closed_at: closed_event&.updated_at,
+                              latest_closed_by: closed_event&.author,
+                              merged_at: merge_event&.updated_at,
+                              merged_by: merge_event&.author)
+  end
 end