Refactor User.find_by_any_email

By using SQL::Union we can return a proper ActiveRecord::Relation,
making it possible to select the columns we're interested in (instead of
all of them).

app/models/user.rb

@@ -269,16 +269,16 @@ class User < ActiveRecord::Base
 
     # Find a User by their primary email or any associated secondary email
     def find_by_any_email(email)
-      sql = 'SELECT *
-      FROM users
-      WHERE id IN (
-        SELECT id FROM users WHERE email = :email
-        UNION
-        SELECT emails.user_id FROM emails WHERE email = :email
-      )
-      LIMIT 1;'
+      by_any_email(email).take
+    end
+
+    # Returns a relation containing all the users for the given Email address
+    def by_any_email(email)
+      users = where(email: email)
+      emails = joins(:emails).where(emails: { email: email })
+      union = Gitlab::SQL::Union.new([users, emails])
 
-      User.find_by_sql([sql, { email: email }]).first
+      from("(#{union.to_sql}) #{table_name}")
     end
 
     def filter(filter_name)

spec/models/user_spec.rb

@@ -841,6 +841,19 @@ describe User do
     end
   end
 
+  describe '.by_any_email' do
+    it 'returns an ActiveRecord::Relation' do
+      expect(described_class.by_any_email('foo@example.com'))
+        .to be_a_kind_of(ActiveRecord::Relation)
+    end
+
+    it 'returns a relation of users' do
+      user = create(:user)
+
+      expect(described_class.by_any_email(user.email)).to eq([user])
+    end
+  end
+
   describe '.search' do
     let!(:user) { create(:user, name: 'user', username: 'usern', email: 'email@gmail.com') }
     let!(:user2) { create(:user, name: 'user name', username: 'username', email: 'someemail@gmail.com') }