Prevent duplicate merge events

app/models/merge_request.rb

@@ -177,15 +177,8 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def merge!(user_id)
+    self.author_id_of_changes = user_id
     self.merge
-
-    Event.create(
-      project: self.project,
-      action: Event::MERGED,
-      target_id: self.id,
-      target_type: "MergeRequest",
-      author_id: user_id
-    )
   end
 
   def automerge!(current_user)

app/observers/activity_observer.rb

@@ -39,4 +39,18 @@ class ActivityObserver < ActiveRecord::Observer
       author_id: record.author_id_of_changes
     )
   end
+
+  def after_merge(record, transition)
+    # Since MR can be merged via sidekiq
+    # to prevent event duplication do this check
+    return true if record.merge_event
+
+    Event.create(
+      project: record.project,
+      target_id: record.id,
+      target_type: record.class.name,
+      action: Event::MERGED,
+      author_id: record.author_id_of_changes
+    )
+  end
 end