Tutorial :How to create nested objects using accepts_nested_attributes_for



Question:

I've upgraded to Rails 2.3.3 (from 2.1.x) and I'm trying to figure out the accepts_nested_attributes_for method. I can use the method to update existing nested objects, but I can't use it to create new nested objects. Given the contrived example:

class Product < ActiveRecord::Base    has_many :notes    accepts_nested_attributes_for :notes  end    class Note < ActiveRecord::Base    belongs_to :product    validates_presence_of :product_id, :body  end  

If I try to create a new Product, with a nested Note, as follows:

params = {:name => 'Test', :notes_attributes => {'0' => {'body' => 'Body'}}}  p = Product.new(params)  p.save!  

It fails validations with the message:

ActiveRecord::RecordInvalid: Validation failed: Notes product can't be blank  

I understand why this is happening -- it's because of the validates_presence_of :product_id on the Note class, and because at the time of saving the new record, the Product object doesn't have an id. However, I don't want to remove this validation; I think it would be incorrect to remove it.

I could also solve the problem by manually creating the Product first, and then adding the Note, but that defeats the simplicity of accepts_nested_attributes_for.

Is there a standard Rails way of creating nested objects on new records?


Solution:1

This is a common, circular dependency issue. There is an existing LightHouse ticket which is worth checking out.

I expect this to be much improved in Rails 3, but in the meantime you'll have to do a workaround. One solution is to set up a virtual attribute which you set when nesting to make the validation conditional.

class Note < ActiveRecord::Base    belongs_to :product    validates_presence_of :product_id, :unless => :nested    attr_accessor :nested  end  

And then you would set this attribute as a hidden field in your form.

<%= note_form.hidden_field :nested %>  

That should be enough to have the nested attribute set when creating a note through the nested form. Untested.


Solution:2

check this document if you use Rails3.

http://api.rubyonrails.org/classes/ActiveRecord/NestedAttributes/ClassMethods.html#label-Validating+the+presence+of+a+parent+model


Solution:3

Ryan's solution is actually really cool. I went and made my controller fatter so that this nesting wouldn't have to appear in the view. Mostly because my view is sometimes json, so I want to be able to get away with as little as possible in there.

class Product < ActiveRecord::Base    has_many :notes    accepts_nested_attributes_for :note  end    class Note < ActiveRecord::Base    belongs_to :product    validates_presence_of :product_id  unless :nested    attr_accessor :nested  end    class ProductController < ApplicationController    def create      if params[:product][:note_attributes]         params[:product][:note_attributes].each { |attribute|             attribute.merge!({:nested => true})      }      end      # all the regular create stuff here    end  end  


Solution:4

Best solution yet is to use parental_control plugin: http://github.com/h-lame/parental_control


Note:If u also have question or solution just comment us below or mail us on toontricks1994@gmail.com
Previous
Next Post »