I have models as follows:

class Entity < ActiveRecord::Base  
  has_many :addresses
  accepts_nested_attributes_for :addresses, :reject_if => lambda { |a| a[:label].blank?} , :allow_destroy => true
end

class Client < Entity
  before_save :set_type

  private
  def set_type
    self.type = "Client"
  end  
end

class Address < ActiveRecord::Base
   belongs_to :entity
end

I have recently implemented accepts_nested_attributes_for on the /clients/new form, as follows:

<% form_for(@client, :html => {:class => 'form'}) do |f| -%>
        <%= f.label :name %>
        <%= f.text_field :name -%>  

        <%= f.label :phone %>
        <%= f.text_field :phone %>

        <% f.fields_for :addresses do |a| %>

            <%= a.label :street %>
            <%= a.text_field :street%>     

            <%= a.label :city %>
            <%= a.text_field :city %>  
      <% end %>
<% end %>

And my controller as follows:

class ClientsController < ApplicationController

  before_filter :load_client , :except => [:index, :new, :create, :render_clients]

  def new
    @client = Client.new
    @client.addresses.build    
  end

  def create

    @client = Client.new(params[:client])

    if @client.save
      flash[:notice] = 'Client has been successfully added'
      redirect_to @client
    else
      render :action => 'new'
    end
  end

The issue is that when the record is saved it gives an error stating: "Entity can't be blank"

I assume it is something to do with the fact that a 'Client' and not an 'Entity' is being added.

Can anyone point me in the right direction?