Rendering a JSON object of a join-model and its associated models

Question

In a Rails ( 4.1.5 / ruby 2.0.0p481 / win64 ) application I have a many-to-many relationship between Student and Course and a join model StudentCourse

Answer 1

Use scope to your advantage:

class Course < ActiveRecord::Base
  # ...
  scope :not_started, -> { joins(:student_courses) \
                                      .where(student_courses: {started: false}) }

  scope :with_classmates, -> { includes(:students) } # use eager loading
end

Then call:

@student.courses.not_started.with_classmates \
                                     .to_json(include: {students: {only: :name}})

Output:

[
    {
        "id": 1,
        "name": "english",
        "description": null,
        "students": [
            {"name": "Aiden"},
            {"name": "Alison"}]},
    {
        "id": 2,
        "name": "music",
        "description": null,
        "students": [
            {"name": "Aiden"},
            {"name": "Alison"}]},
    {
        "id": 3,
        "name": "dance",
        "description": null,
        "students": [
            {"name": "Aiden"}]}]