LEFT OUTER JOIN in Rails 4

Question

I have 3 models:

class Student < ActiveRecord::Base
  has_many :student_enrollments, dependent: :destroy
  has_many :courses, through: :student_enrollment         


        

Answer 1

Adding to the answer above, to use includes, if you want an OUTER JOIN without referencing the table in the where (like id being nil) or the reference is in a string you can use references. That would look like this:

Course.includes(:student_enrollments).references(:student_enrollments)

or

Course.includes(:student_enrollments).references(:student_enrollments).where('student_enrollments.id = ?', nil)

http://api.rubyonrails.org/classes/ActiveRecord/QueryMethods.html#method-i-references