Getting fields_for and accepts_nested_attributes_for to work with a belongs_to relationship

Question

I cannot seem to get a nested form to generate in a rails view for a belongs_to relationship using the new accepts_nested_attributes_for facility of Rails 2.3. I did check out many of the resources available and it looks like my code should be working, but fields_for explodes on me, and I suspect that it has something to do with how I have the nested models configured.

The error I hit is a common one that can have many causes:

'@account[owner]' is not allowed as an instance variable name 

Here are the two models involved:

class Account < ActiveRecord::Base   # Relationships   belongs_to :owner, :class_name => 'User', :foreign_key => 'owner_id'   accepts_nested_attributes_for :owner   has_many :users end  class User < ActiveRecord::Base   belongs_to :account end 

Perhaps this is where I am doing it 'rong', as an Account can have an 'owner', and may 'users', but a user only has one 'account', based on the user model account_id key.

This is the view code in new.html.haml that blows up on me:

- form_for :account, :url => account_path do |account|   = account.text_field :name   - account.fields_for :owner do |owner|     = owner.text_field :name 

And this is the controller code for the new action:

class AccountsController < ApplicationController   # GET /account/new   def new     @account  = Account.new   end end 

When I try to load /account/new I get the following exception:

NameError in Accounts#new Showing app/views/accounts/new.html.haml where line #63 raised: @account[owner] is not allowed as an instance variable name 

If I try to use the mysterious 'build' method, it just bombs out in the controller, perhaps because build is just for multi-record relationships:

class AccountsController < ApplicationController   # GET /account/new   def new     @account  = Account.new     @account.owner.build   end end  You have a nil object when you didn't expect it! The error occurred while evaluating nil.build 

If I try to set this up using @account.owner_attributes = {} in the controller, or @account.owner = User.new, I'm back to the original error, "@account[owner] is not allowed as an instance variable name".

Does anybody else have the new accepts_nested_attributes_for method working with a belongs_to relationship? Is there something special or different you have to do? All the official examples and sample code (like the great stuff over at Ryans Scraps) is concerned with multi-record associations.

Answer 1

I'm a few months too late, but I was looking to solve this error and my situation was that I could not change the relationship to 'face the other way'.

The answer really is quite simple, you have to do this in your new action:

@account.build_owner 

The reason why the form did not display using fields_for was because it did not have a valid object. You had the right idea up there with:

@account.owner.build 

However, this is not the way belongs_to work. This method is only generated with has_many and has_and_belongs_to_many.

Reference: http://guides.rubyonrails.org/association_basics.html#belongs-to-association-reference