Improve change group ownership logic

app/controllers/admin/groups_controller.rb

@@ -34,7 +34,7 @@ class Admin::GroupsController < Admin::ApplicationController
     owner_id =group_params.delete(:owner_id)
 
     if owner_id
-      @group.owner = User.find(owner_id)
+      @group.change_owner(User.find(owner_id))
     end
 
     if @group.update_attributes(group_params)

app/models/group.rb

@@ -32,6 +32,17 @@ class Group < Namespace
     end
   end
 
+  def change_owner(user)
+    self.owner = user
+    membership = users_groups.where(user_id: user.id).first
+
+    if membership
+      membership.update_attributes(group_access: UsersGroup::OWNER)
+    else
+      add_owner
+    end
+  end
+
   private
 
   def add_owner