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?

Does it work if you use "build" instead of "new" on the second example? Sometime ago they used to be different methods, I'm not sure for ROR4 — AndreDurao, Dec 31 '20 at 21:46
Does this answer your question? [using has\_many :through and build](https://stackoverflow.com/questions/9346261/using-has-many-through-and-build) — Eyeslandic, Dec 31 '20 at 22:03

score -2 · Answer 1 · edited Jan 05 '21 at 15:47

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

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

1 Answers1