I have 3 models/tables: Instructors, Courses, InstructorCourses

InstructorCourses shows which instructors can teach a course (instructor_id and course_id). There can be many instructors for a given course.

I am trying to retrieve the courses an instructor can teach. So far, I have:

$courses = $this->Courses->find('all')
        ->where(['Courses.active' => 1])
        ->contain([
        	'InstructorCourses' => [
	        	'conditions' => ['InstructorCourses.instructor_id' => $instructor_id],
        	]
        ])->order(['Courses.date_start ASC']);

But this is returning all courses. What is the best way to go about this?