Setting has_many :through with a form on rails 3

Question

I'm trying to create user roles for my user using a form,

<%= form_for @user do |f| %>
  <%= f.error_messages %>
  <p>
    <%= f.label :username %><br />
    <%= f.text_field :username %>
  </p>
  <p>
    <%= f.label :email, "Email Address" %><br />
    <%= f.text_field :email %>
  </p>
  <p>
    <%= f.label :password %><br />
    <%= f.password_field :password %>
  </p>
  <p>
    <%= f.label :password_confirmation, "Confirm Password" %><br />
    <%= f.password_field :password_confirmation %>
  </p>

  <% # f.select :roles, Role.all.map {|r| [r.title]} %>

  <% Role.all.each do |role| %>
    <div>
      <%= check_box_tag :role_ids, role.id, @user.roles.include?(role), :name => 'user[role_ids][]' -%>
      <%= label_tag :role_ids, role.title -%>
    </div>
  <% end -%>

  <p><%= f.submit (@user.new_record? ? "Sign up" : "Update"), :id => :sign_up %></p>
<% end %>

This is the association that I have in my model

class user < ActiveRecord::Base
  has_many :assignments
  has_many :roles, :through => :assignments
end

class assignment < ActiveRecord::Base
  belongs_to :user
  belongs_to :role
end

class role < ActiveRecord::Base
  has_many :assignments
  has_many :users, :through => :assignments
end

What's the way to create the assignment between the user and the role by using the form that I presented in the beginning ?

My create action in my user controller looks like:

def create
   @user = User.new(params[:user])
    if @user.save
      session[:user_id] = @user.id
      render :action => 'dashboard'
    else
      render :action => 'new'
    end
  end

When I send my form I get the error:

ActiveRecord::AssociationTypeMismatch in UsersController#create

Role(#70331681817580) expected, got String(#70331650003400)

Request

Parameters:

{"utf8"=>"✓",
 "authenticity_token"=>"WHpOW+DmymZ2pWmY9NHSuodf2vjyKdgMNZcc8NvCNa0=",
 "user"=>{"username"=>"ioio",
 "email"=>"ioio@ioio.com",
 "password"=>"[FILTERED]",
 "password_confirmation"=>"[FILTERED]",
 "roles"=>["2"]},   #### <<< ==== This is the checkbox that I selected for this request.
 "commit"=>"Sign up"}

Any help is welcome.

Answer 1

Using your current form and based on:

<%= check_box_tag :role_ids, role.id, @user.roles.include?(role), :name => 'user[role_ids][]' -%>

On submit, your params should look like (note 'role_ids' and not 'roles'):

Request

Parameters:

{"utf8"=>"✓",
 "authenticity_token"=>"WHpOW+DmymZ2pWmY9NHSuodf2vjyKdgMNZcc8NvCNa0=",
 "user"=>{"username"=>"ioio",
 "email"=>"ioio@ioio.com",
 "password"=>"[FILTERED]",
 "password_confirmation"=>"[FILTERED]",
 "role_ids"=>["2"]},   #### <<< ==== This is the checkbox that I selected for this request.
 "commit"=>"Sign up"}

if this is the case, you will have to instance your roles and set them for the user in the controller:

    def create
      @user = User.new(params[:user])
      roles = Role.find(params[:user][:role_ids]) rescue []
      @user.roles = roles
      if @user.save
        session[:user_id] = @user.id
        render :action => 'dashboard'
      else
        render :action => 'new'
      end
    end

...and similarly:

   def update
     @user = User.where(:username=>params[:id]).first
     roles = Role.find(params[:user][:role_ids]) rescue []
     @user.roles = roles
     if @user.update_attributes(params[:user])
       redirect_to users_url, :notice  => "Successfully updated user."
     else
      render :action => 'edit'
     end
   end

Answer 2

The error message gives you the hint: To be able to save the user object you first need to create the associated Role objects somehow. At the moment you only have an array of strings that are Role ids.

You need to use the accepts_nested_attributes_for method on the user model.