1 files changed, 37 insertions, 0 deletions
diff --git a/app/models/concerns/from_except.rb b/app/models/concerns/from_except.rb
new file mode 100644
index 00000000000..b9ca9dda4b0
--- /dev/null
+++ b/app/models/concerns/from_except.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+module FromExcept
+  extend ActiveSupport::Concern
+
+  class_methods do
+    # Produces a query that uses a FROM to select data using an EXCEPT.
+    #
+    # Example:
+    #     groups = Group.from_except([group1.self_and_hierarchy, group2.self_and_hierarchy])
+    #
+    # This would produce the following SQL query:
+    #
+    #     SELECT *
+    #     FROM (
+    #       SELECT "namespaces". *
+    #       ...
+    #
+    #       EXCEPT
+    #
+    #       SELECT "namespaces". *
+    #       ...
+    #     ) groups;
+    #
+    # members - An Array of ActiveRecord::Relation objects to use in the except.
+    #
+    # remove_duplicates - A boolean indicating if duplicate entries should be
+    #                     removed. Defaults to true.
+    #
+    # alias_as - The alias to use for the sub query. Defaults to the name of the
+    #            table of the current model.
+    # rubocop: disable Gitlab/Except
+    extend FromSetOperator
+    define_set_operator Gitlab::SQL::Except
+    # rubocop: enable Gitlab/Except
+  end
+end