Added Gitlab::SQL::Union class

This class can be used to join multiple AcitveRecord::Relation objects
together using a SQL UNION statement. ActiveRecord < 5.0 sadly doesn't
support UNION and existing Gems out there don't handle prepared
statements (e.g. they never incremented the variable bindings).

1 files changed, 16 insertions, 0 deletions

diff --git a/spec/lib/gitlab/sql/union_spec.rb b/spec/lib/gitlab/sql/union_spec.rb
new file mode 100644
index 00000000000..976360af9b5
--- /dev/null
+++ b/spec/lib/gitlab/sql/union_spec.rb
@@ -0,0 +1,16 @@
+require 'spec_helper'
+
+describe Gitlab::SQL::Union do
+  describe '#to_sql' do
+    it 'returns a String joining relations together using a UNION' do
+      rel1  = User.where(email: 'alice@example.com')
+      rel2  = User.where(email: 'bob@example.com')
+      union = described_class.new([rel1, rel2])
+
+      sql1 = rel1.reorder(nil).to_sql
+      sql2 = rel2.reorder(nil).to_sql
+
+      expect(union.to_sql).to eq("(#{sql1}) UNION (#{sql2})")
+    end
+  end
+end