Nested Attributes Child model don't save - ruby-on-rails

Question

I'm having a problem in the model saving with nested attributes.
In the app, there's a Customer, that have 1..n Contacts witch in turn have 1..n Telephones.
I've searched a lot before asking here, and decided to make it save only the Contact first. Well, at first the Customer is stored, but Contact is not. From what I read there's no need to repeat the ... contacts.build from new function in the create, and that the line "#customer = Customer.new(customer_params)" would create and store them both.
Why it's not working? (That's the first question.)
After some modifications and debugging, I found that when I set a second line building Contact (...contacts.build(customer_params[:contacts_attributes])) it's not saved because of an error of 'unknown attribute'. That's because between the hash :contacts_attribute and the content of it, it's added another hash, called ':0' (?). The structure of the hash that comes from the form is this :
":contacts_attribute[:0[:name, :department, :email]]"
I imagine that this hash :0 is for adding more than one Contact instance, that will come in hashes :1, :2 etc.
There's a way to store the Contact instance by getting this :0 hash? (How do I access this hash? Is it "... :contacts_attribute[0]"?)
Below is the relevant code.
Thanks for the attention!
customer.rb
class Customer < ActiveRecord::Base
...
has_many :contacts
accepts_nested_attributes_for :contacts, reject_if: lambda {|attributes| attributes['kind'].blank?}
...
def change_by(user_id)
update_attributes(changed_by: user_id, deleted_at: Time.now, updated_at: Time.now)
end
def delete(user_id)
update_attributes(status: false, changed_by: user_id, deleted_at: Time.now, updated_at: Time.now)
end
private
...
end
customers_controller.rb
class CustomersController < ApplicationController
def new
#customer = Customer.new
#customer.contacts.new
end
def create
user_id = session[:user_id]
#customer = Customer.new(customer_params)
if #customer.save
#customer.change_by(user_id)
flash[:success] = "Cliente cadastrado com sucesso!"
redirect_to customers_url
else
render 'new'
end
end
private
def customer_params
params.require(:customer).permit(:razao_social, :nome, :CPF_CNPJ,
:adress_id, :email_nota, :transporter_id, :observacao,
contacts_attributes: [:nome, :setor, :email])
end
Form
<div class="row">
<div class="col-md-6 col-md-offset-3">
<%= form_for #customer do |f| %>
<%= f.label "Dados Básicos" %>
<div class="well">
<%= f.label :razao_social, "Razão Social" %>
<%= f.text_field :razao_social %>
<%= f.label :nome, "Nome" %>
<%= f.text_field :nome %>
<%= f.label :CPF_CNPJ, "CPF/CNPJ" %>
<%= f.text_field :CPF_CNPJ %>
<%= f.label :email_nota, "Email para nota" %>
<%= f.email_field :email_nota %>
<%= f.label :observacao, "Observações" %>
<%= f.text_area :observacao %>
</div>
<%= f.fields_for :contacts do |k| %>
<%= k.label "Contato" %>
<div class="well">
<%= k.label :nome, "Nome" %>
<%= k.text_field :nome %>
<%= k.label :setor, "Setor" %>
<%= k.text_field :setor %>
<%= k.label :email, "Email" %>
<%= k.email_field :email %>
</div>
<% end %>
<%= f.submit "Cadastrar Cliente", class: "btn btn-primary" %>
<% end %>
</div>

Answer 1

reject_if: lambda {|attributes| attributes['kind'].blank?}
No sign of :kind in your form or your customer_params
This might have something to do with it.
Other than that, if you need an add/remove relationship for contacts, check out the cocoon gem. If you only need one, then build that into your fields for:
<%= f.fields_for :contacts, #customer.contacts.first || #customer.contacts.build do |k| %>
The form will then be specific to a single instance of contact.
There's a way to store the Contact instance by getting this :0 hash?
(How do I access this hash? Is it "... :contacts_attribute[0]"?)
You don't need to access it, that's what the accepts_nested_attributes is for. The rest of your code looks ok so sort out the rejection issue at the top and come back if there are still problems, and post the log output - specifically the params hash for the request!