Felipe Artur
--- a/app/models/todo.rb
+++ b/app/models/todo.rb

  after_save :keep_around_commit

+  class << self
+    def sort(method)
+      method == "priority" ? order_by_labels_priority : order_by(method)
+    end
+
+    # Order by priority depending on which issue/merge request the Todo belongs to
+    # Todos with highest priority first then oldest todos
+    def order_by_labels_priority
+      select('todos.*').from('todos').
+        joins('LEFT JOIN label_links ON (todos.target_id = label_links.target_id AND label_links.target_type = todos.target_type)').
+        joins('LEFT JOIN labels ON label_links.label_id = labels.id').
+        order(Gitlab::Database.nulls_last_order('labels.priority', 'ASC')).