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?

ryanb · Accepted Answer · 2009-07-31 22:14:21Z

16

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.

answered Jul 31, 2009 at 22:14

ryanb

16.3k5 gold badges53 silver badges46 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Casper Fabricius Over a year ago

In Rails 3 this problem is solved by the added :inverse_of option to has_many, has_one and belongs_to. See e.g. daokaous.com/rails3.0.0_doc/classes/ActiveRecord/Associations/… under the section "Bi-directional associations"

aceofspades Over a year ago

I've opted to disable the validation when :id == nil. Since that should only happen when writing a new, nested record, I'm hoping that will be safe. Odd that this issue made it all the way to 2.3.8.

DGM Over a year ago

inverse_of doesn't seem to work when both the record's parent doesn't exist yet, and thus no id can be tested. Looks like this nested hack is the only way through. :(

Raphael Over a year ago

I'm experiencing this issue in Rails 3, any updates on how to solve it?

kuboon · Accepted Answer · 2012-09-26 01:21:39Z

7

check this document if you use Rails3.

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

answered Sep 26, 2012 at 1:21

kuboon

10.3k3 gold badges46 silver badges33 bronze badges

2 Comments

kuboon Over a year ago

very important point is you should validate presence of "product" not "product_id"

quainjn Over a year ago

I think kuboon has the right answer. Validate presence of "product", not "product_id" along with changing the association on Product to "has_many :notes, inverse_of: :product" should do it.

Graeme Worthy · Accepted Answer · 2010-01-22 04:18:01Z

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

Dmitry Polushkin · Accepted Answer · 2009-11-19 08:48:46Z

0

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

answered Nov 19, 2009 at 8:48

Dmitry Polushkin

3,4332 gold badges42 silver badges47 bronze badges

Collectives™ on Stack Overflow

How to create nested objects using accepts_nested_attributes_for

4 Answers 4

4 Comments

2 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

4 Comments

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related