Why isnt the join table for has_many through created in rails when using new/save versus create?

Question

This is on rails 4.2.11.3. I have a has_many through relationship set up like this:

class ProgramCourse < ActiveRecord::Base
  belongs_to :course
  belongs_to :program
end

class Course < ActiveRecord::Base
  has_many :program_courses
  has_many :programs, -> { uniq }, through: :program_courses
end

class Program < ActiveRecord::Base
  has_many :program_courses
  has_many :courses, -> { uniq }, through: :program_courses
end

If I create a course like this:

c = program.courses.create(name: 'Amazing Course')

The ProgramCourse record is created along with the new Course . However, if I do so like this:

c = program.courses.new(name: 'Amazing Course')
c.save

Only the Course is created. Is this a bug? Is there something syntactically off with my relationship? Can anyone explain why these two are different?

Answer 1

class ProgramCourse < ActiveRecord::Base
  belongs_to :course
  belongs_to :program
end

class Course < ActiveRecord::Base
  has_many :program_courses
  has_many :programs, -> { uniq }, through: :program_courses
end

class Program < ActiveRecord::Base
  has_many :program_courses
  has_many :courses, -> { uniq }, through: :program_courses
  accepts_nested_attributes_for :program_courses, :courses
end

You need to add this in the model to use this or you can use the build method to create the associated record

c = program.courses.build(name: 'Amazing Course')
c.save