1 files changed, 19 insertions, 0 deletions
diff --git a/app/models/concerns/from_set_operator.rb b/app/models/concerns/from_set_operator.rb
new file mode 100644
index 00000000000..593fd251c5c
--- /dev/null
+++ b/app/models/concerns/from_set_operator.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+module FromSetOperator
+  # Define a high level method to more easily work with the SQL set operations
+  # of UNION, INTERSECT, and EXCEPT as defined by Gitlab::SQL::Union,
+  # Gitlab::SQL::Intersect, and Gitlab::SQL::Except respectively.
+  def define_set_operator(operator)
+    method_name = 'from_' + operator.name.demodulize.downcase
+    method_name = method_name.to_sym
+
+    raise "Trying to redefine method '#{method(method_name)}'" if methods.include?(method_name)
+
+    define_method(method_name) do |members, remove_duplicates: true, alias_as: table_name|
+      operator_sql = operator.new(members, remove_duplicates: remove_duplicates).to_sql
+
+      from(Arel.sql("(#{operator_sql}) #{alias_as}"))
+    end
+  end
+end