How can I do a LEFT OUTER JOIN using Rails ActiveRecord?

Question

I don\'t have any ideas. Could you give me any clues (like reference sites). Any help will be appreciated.

Model1: GROUP         


        

Answer 1

You can do this in rails 3.x regardless if you are referencing the table or not in a where clause:

Group.eager_load(:user_group_cmb)

...and it will perform a left outter join

Answer 2

The problem with the accepted answer is that it will actually do a LEFT INNER JOIN technically because it won't display entries where the user_group_cmbs. user_id is null (which would be the reason to do a LEFT OUTER JOIN).

A working solution is to use #references:

Group.includes(:user_group_cmb).references(:user_group_cmb)

Or the even more convenient #eager_load:

Group.eager_load(:user_group_cmb)

Read the more detailed explanation here.