Selective delete from join tables

rubyonrails-talk
#1

Hi,

I'm learning rails and have run into what for me is a difficult problem.
I have the following associations with a galleries_pictures and a
pictures_questions join table:

class Picture < ActiveRecord::Base
  has_and_belongs_to_many :questions
  has_and_belongs_to_many :galleries

class Question < ActiveRecord::Base
  has_and_belongs_to_many :pictures

class Gallery < ActiveRecord::Base
  has_and_belongs_to_many :pictures

In the edit question view, a question and its associated picture(s) can
be edited. My problem is, I cannot figure out how to delete the picture
in the question and at the same time not delete it from the gallery ie
delete the pictures_questions association but not the
galleries_pictures association.

The action called from the view deletes the row in both join tables:
def destroy
    @picture = Picture.find(params[:id])
    @picture.destroy

Thanks!

#2

http://guides.rubyonrails.org/association_basics.html#has_and_belongs_to_many-association-reference

#3

Dave Castellano wrote in post #1110796:

Hi,

I'm learning rails and have run into what for me is a difficult problem.
I have the following associations with a galleries_pictures and a
pictures_questions join table:

class Picture < ActiveRecord::Base
  has_and_belongs_to_many :questions
  has_and_belongs_to_many :galleries

class Question < ActiveRecord::Base
  has_and_belongs_to_many :pictures

class Gallery < ActiveRecord::Base
  has_and_belongs_to_many :pictures

In the edit question view, a question and its associated picture(s) can
be edited. My problem is, I cannot figure out how to delete the picture
in the question and at the same time not delete it from the gallery ie
delete the pictures_questions association but not the
galleries_pictures association.

The action called from the view deletes the row in both join tables:
def destroy
    @picture = Picture.find(params[:id])
    @picture.destroy

Thanks!

Here you are destroying the picture object so naturally Rails will
manage the associations automatically. What you want to do instead is
to delete the association not the actual picture object.

There are a couple of ways to do this. But, you do not wan to use the
destroy action on pictures_controller. That action should be used to
destroy pictures not associations.

Option 1—Expose the join model and manage the association with standard
REST destroy action on the association model:

class Picture < ActiveRecord::Base
  has_many :question_pictures
  has_many :questions, :through => :question_pictures
end

class Question < ActiveRecord::Base
  has_many :question_pictures
  has_many :pictures, :through => :question_pictures
end

class QuestionPicture < ActiveRecord::Base
  belongs_to :question
  belongs_to :picture
end

question_pictures_controller

#4

P.S. None of this code has been tested. Just wrote it by memory.

Thank you. I get it. It worked well with a couple of small tweaks.
...wish I could do that from memory :slight_smile:

Thanks,
Dave