LabelsFinder inherits from UnionFinder

app/finders/labels_finder.rb

-class LabelsFinder
+class LabelsFinder < UnionFinder
   def initialize(current_user, params = {})
     @current_user = current_user
     @params = params
   end
 
   def execute
-    items = init_collection
+    items = find_union(label_ids, Label)
     items = with_title(items)
     sort(items)
   end
@@ -14,15 +14,10 @@ class LabelsFinder
 
   attr_reader :current_user, :params
 
-  def init_collection
+  def label_ids
     label_ids = []
     label_ids << Label.where(group_id: projects.where.not(group: nil).select(:namespace_id)).select(:id)
-    label_ids << Label.where(project_id: projects).select(:id)
-
-    union = Gitlab::SQL::Union.new(label_ids)
-
-    Label.where("labels.id IN (#{union.to_sql})")
-         .reorder(title: :asc)
+    label_ids << Label.where(project_id: projects.select(:id)).select(:id)
   end
 
   def with_title(items)