Question

I have isolated the problem in the second block of code below (if you don’t want all the details): I can create new users from the account model. I can’t assign those users roles from the accounts model. I am using fields_for, this method does not work when I attempt to assign the role_ids to the roles model. My db is set up in the following way:

1. Account model has_many :users

2. User model has_and_belongs_to_many :roles,
   belongs_to :accounts

3. Roles model has_and_belongs_to_many :users

views/accounts/new.html.erb

<% for user in @account.users %>
 <% fields_for "account[user_attributes][]", user do |account_fields| %>
      <p>Login  : <%= account_fields.text_field :login %>
      <p>Email  : <%= account_fields.text_field :email %>
      <p>Password  : <%= account_fields.password_field :password %>
      <p>Confirm Password  : <%= account_fields.password_field :password_confirmation %>
      <%= account_fields.hidden_field :account_id, :value => :id %>

    <% end %>
<% end %>

<% for role in @account.users.first.roles %>
<% fields_for "account[role_attributes]]", role do |role_fields| %>
  <%= role_fields.hidden_field :role_ids, :value => '[1]' %>
 <% end %>
<% end%>

Associated setter methods in the account.rb model: using the stacktrace I have isolated the problem to “undefined method `roles’ for #” on line 34, marked below:

def user_attributes=(user_attributes)
   user_attributes.each do |attributes|
   users.build(attributes)
   end
end

def role_attributes=(role_attributes)
    role_attributes.each do |attributes|
    users.roles.build(attributes)   #error here (stacktrace)
  end
end

finally, within the accounts controller I build the users and roles in memory:

 def new
    @account = Account.new
    1.times { @account.users.build }
    1.times { @account.users.first.roles.build }

The @accounts.users.first.roles.build proof from consol:

>> account
=> #<Account id: 1, subdomain: "justinzollars", created_at: "2010-02-08 14:41:13", updated_at: "2010-02-08 14:41:13">
>> account.users
=> [#<User id: 13, login: "jayz", email: "[e-mail]", crypted_password: "f9a3d618fc650d285a90f9775508c13784891b97", salt: "f497a7dd909b695caff1f6310e710245615d55b6", created_at: "2010-02-08 20:25:48", updated_at: "2010-02-08 20:25:48", remember_token: nil, remember_token_expires_at: nil, account_id: 1>, #<User id: 16, login: "jasonwade23", email: "[e-mail]", crypted_password: "06581b47cfac7a529773d61dc0b1d5d6c0da6c08", salt: "93f8b99cd9da60b904d553fcc7843bfb66352c3e", created_at: "2010-02-13 07:46:14", updated_at: "2010-02-13 07:46:14", remember_token: nil, remember_token_expires_at: nil, account_id: 1>]
>> account.users.first
=> #<User id: 13, login: "jayz", email: "[e-mail]", crypted_password: "f9a3d618fc650d285a90f9775508c13784891b97", salt: "f497a7dd909b695caff1f6310e710245615d55b6", created_at: "2010-02-08 20:25:48", updated_at: "2010-02-08 20:25:48", remember_token: nil, remember_token_expires_at: nil, account_id: 1>
>> account.users.first.roles
=> [#<Role id: 1, name: "admin">, #<Role id: 2, name: "alt">]
>> 

Answer 1

You should use accepts_nested_attributes_for, so in models:

# Account model
accepts_nested_attributes_for :users

# User model
accepts_nested_attributes_for :roles

Then you should remove user_attributes= and role_attributes= methods.
Your form should look like this:

<% form_for @account do |f| %>
   <% fields_for :users do |u| %>
      ... # user fields
      <% fields_for :roles do |r| %>
         ... # role fields
      <% end %>
   <% end %>
   <%= f.submit 'Save' %>
<% end %>

It will automaticaly iterate over all users associated with account and all roles associated with user.

For more details read here.

EDIT:
You can assign roles to user, in controller:

role = Roles.find(some_id)
@user.roles << role

or

@user.role_ids = [2, 4, 6]

However I’m not sure how to add roles with has_and_belongs_to_many association. You are using @user.roles.build method which will create new role and associate it with user. If you want to add a role you should do it with one of two examples above. But how to create a from for it? I don’t know. I would add a model for users_roles table and add to user model:

has_many :users_roles
accepts_nested_attributes_for :users_roles # you should add here also some :reject_if

Then insted of fields_for :roles I would add in form:

<% fields_for :users_roles do |ur| %>
  <%= ur.select :role_id, Role.all.collect {|r| [r.name, r.id] }, {:include_blank => true} %>
<% end %>

Then in your controller you should add something like 3.times { @user.users_roles.build }. If you want to have nice “Add” and “Remove” links that create for you new role with javascript, take a look here – it is really nice example how to handle it.