Rails 4 - Add existing association in nested resource

Question

I have 3 models:

class Resource < ActiveRecord::Base
  has_many :blocks
  has_many :topics, :through => :blocks, dependent: :destroy

class Topic < ActiveRecord::Base
  has_many :blocks
  has_many :resources, :through => :blocks, :class_name => 'Resource', dependent: :destroy
  accepts_nested_attributes_for :resources
  accepts_nested_attributes_for :blocks, :allow_destroy => true

class Block < ActiveRecord::Base
  belongs_to :resource
  belongs_to :topic
  accepts_nested_attributes_for :resource, :allow_destroy => true, :reject_if => :all_blank

My routes:

namespace :admin do
  resources :topics do
    resources :resources do
      post :link
      delete :unlink

Everything works fine except that I'd like to have in the "Add resource" a way to select an existing resource (in a drop down) in addition to create a new one (which works fine).

So, I'd like a drop down showing all the resources, then adding the one I selected to the Block model. In other words, I need to only create the association between the topic and the ressource (via the Block model).

I'm able to do it when I have all a multi-select but I'm banging my head to have it available with one resource only (adding it on the ones already selected).

Am I clear? :/

Thanks! - Vincent

Answer 1

If you got a complicated logic like this, it's better to use something like "Form Objects" to save multiple models and relations between them. I.e. move saving logic outside of both models.

access_nested_attributes_for should be used only for very very simple cases (like most of Rails's magical features)