I am not really understand how's the nested attributes work in Rails.

I have 2 models, Accounts and Users. Accounts has_many Users. When a new user filled in the form, Rails reported

User(#2164802740) expected, got Array(#2148376200)

Is that Rails cannot read the nested attributes from the form? How can I fix it? How can I save the data from nested attributes form to database?

Thanks all~

Here are the MVCs:

Account Model

class Account < ActiveRecord::Base
  has_many :users
  accepts_nested_attributes_for :users

  validates_presence_of       :company_name, :message => "companyname is required."
  validates_presence_of       :company_website, :message => "website is required."
end

User Model

class User < ActiveRecord::Base
  belongs_to :account

  validates_presence_of         :user_name, :message => "username too short."
  validates_presence_of         :password, :message => "password too short."
end

Account Controller

class AccountController < ApplicationController
  def new
  end

  def created
  end

  def create
    @account = Account.new(params[:account])
    if @account.save
      redirect_to :action => "created"
    else
      flash[:notice] = "error!!!"
      render :action => "new"
    end
  end
end

Account/new View

<h1>Account#new</h1>

<% form_for :account, :url => { :action => "create" } do |f| %>
    <% f.fields_for :users do |ff| %>
    <p>
        <%= ff.label :user_name %><br />
        <%= ff.text_field :user_name %>
    </p>
    <p>
        <%= ff.label :password %><br />
        <%= ff.password_field :password %>
    </p>
    <% end %>
    <p>
        <%= f.label :company_name %><br />
        <%= f.text_field :company_name %>
    </p>
    <p>
        <%= f.label :company_website %><br />
        <%= f.text_field :company_website %>
    </p>
<% end %>

Account Migration

class CreateAccounts < ActiveRecord::Migration
  def self.up
    create_table :accounts do |t|
      t.string :company_name
      t.string :company_website

      t.timestamps
    end
  end

  def self.down
    drop_table :accounts
  end
end

User Migration

class CreateUsers < ActiveRecord::Migration
  def self.up
    create_table :users do |t|
      t.string :user_name
      t.string :password
      t.integer :account_id

      t.timestamps
    end
  end

  def self.down
    drop_table :users
  end
end

Thanks everyone. :)