Error on update for a 3 columns join table

I have a problem while updating a 3 keys join table. I've been on this for quite a while now and have no idea how to fix it. In short, to be able to get the new project working, I had to set these two habtm declaration (in /models/project.rb):

has_and_belongs_to_many :users, 
    :join_table => "projects_roles_users",
    :foreign_key => 'property_id',
    :association_foreign_key => 'user_id',
    :insert_sql => 'INSERT INTO
                projects_roles_users(project_id,role_id,user_id) 
                VALUES(#{id}, #{role_ids}, #{user_ids})',
    :delete_sql => 'DELETE FROM projects_roles_users 
                    WHERE projects_roles_users.property_id = #{id}'

  has_and_belongs_to_many :roles, 
     :join_table => "projects_roles_users",
     :foreign_key => 'project_id',
     :association_foreign_key => 'role_id',
     :insert_sql => 'INSERT INTO
                projects_roles_users(project_id,role_id,user_id) 
                VALUES(#{id}, #{role_ids}, #{user_ids})',
     :delete_sql => 'DELETE FROM projects_roles_users 
                     WHERE projects_roles_users.project_id = #{id}' 

So the new project works just fine (although I get duplicates in project_roles_users). However, when I want to update the role a user has in a project, I get this error:

Mysql::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ' 1414)' at line 3: INSERT INTO
                projects_roles_users(project_id,role_id,user_id) 
                VALUES(29, , )

Here's the controller:

  def update
    @project = Project.find(params[:id])

    respond_to do |format|
      if @project.update_attributes(params[:project])
        flash[:notice] = 'Project was successfully updated.'
        format.html { redirect_to user_path(current_user.id) }
        format.xml  { head :ok }
      else
        format.html { render :action => "edit" }
        format.xml  { render :xml => @project.errors, :status => :unprocessable_entity }
      end
    end
  end

And here's the view:

<% form_for(@project,:html => { :multipart => true }) do |f| %>
  <%= f.error_messages %>

  <p>
    <%= f.label :name %><br />
    <%= f.text_field :name %>
  </p>

  <p>
    <% f.label :role, 'Role' %><br />
    <%= f.collection_select :role_ids, Role.find(:all, :order => 'position'), :id, :role, {}, :multiple => false %>     
  </p>        

  <%= f.hidden_field :user_ids, :value => current_user.id %>

  <p>
    <%= f.submit 'Update' %>
  </p>
<% end %>

<%= link_to 'Show', @project %> |
<%= link_to 'Back', projects_path %>
<%= javascript_tag "$('address').focus()" %>

Finally, here's the log (maybe it'll help you figure it out...):

Processing ProjectsController#update (for 127.0.0.1 at 2011-02-23 08:43:29) [PUT]
  Parameters: {"project"=>{"price"=>"12$", "city"=>"City", "address"=>"452 Street st.", "user_ids"=>"14", "role_ids"=>["2"], "postalcode"=>"12346", "description"=>"Description", "state"=>"State"}, "commit"=>"Update", "authenticity_token"=>"OKQaW4LPb3Xye6Kbh/W2EgxPWFe4aj26etIEVlCTKTg=", "id"=>"29"}
  User Columns (0.9ms)   SHOW FIELDS FROM `users`
  User Load (0.1ms)   SELECT * FROM `users` WHERE (`users`.`id` = 14) LIMIT 1
  Page Load (0.1ms)   SELECT * FROM `pages` WHERE (parent_id IS NULL) ORDER BY position
  Project Columns (0.9ms)   SHOW FIELDS FROM `projects`
  Project Load (0.1ms)   SELECT * FROM `projects` WHERE (`properties`.`id` = 29) 
  SQL (0.1ms)   BEGIN
  R开发者_如何学编程ole Columns (0.8ms)   SHOW FIELDS FROM `roles`
  Role Load (0.1ms)   SELECT * FROM `roles` WHERE (`roles`.`id` = 2) 
  projects_roles_users Columns (0.5ms)   SHOW FIELDS FROM `projects_roles_users`
  Role Load (0.3ms)   SELECT * FROM `roles` INNER JOIN `projects_roles_users` ON `roles`.id = `projects_roles_users`.role_id WHERE (`projects_roles_users`.project_id = 29 ) 
  User Load (0.3ms)   SELECT `users`.id FROM `users` INNER JOIN `projects_roles_users` ON `users`.id = `projects_roles_users`.user_id WHERE (`projects_roles_users`.project_id = 29 ) 
  SQL (0.1ms)   DELETE FROM projects_roles_users 
 WHERE projects_roles_users.project_id = 29
  User Load (0.2ms)   SELECT `users`.id FROM `users` INNER JOIN `projects_roles_users` ON `users`.id = `properties_roles_users`.user_id WHERE (`projects_roles_users`.project_id = 29 ) 
  SQL (0.1ms)   DELETE FROM projects_roles_users 
 WHERE projects_roles_users.project_id = 29
  SQL (0.5ms)   describe `projects_roles_users`
  User Load (0.3ms)   SELECT `users`.id FROM `users` INNER JOIN `projects_roles_users` ON `users`.id = `projects_roles_users`.user_id WHERE (`projects_roles_users`.project_id = 29 ) 
  SQL (0.0ms)   Mysql::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ' 1414)' at line 3: INSERT INTO
 projects_roles_users(project_id,role_id,user_id) 
 VALUES(29, , )
  SQL (0.1ms)   ROLLBACK

ActiveRecord::StatementInvalid (Mysql::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ' 1414)' at line 3: INSERT INTO
                projects_roles_users(project_id,role_id,user_id) 
                VALUES(29, , )):
  app/controllers/properties_controller.rb:71:in `update'
  app/controllers/properties_controller.rb:70:in `update'

Rendered rescues/_trace (136.5ms)
Rendered rescues/_request_and_response (0.6ms)
Rendering rescues/layout (internal_server_error)

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You really don't want to use HABTM anymore. Promote the join to a full-fledged model and use has many through associations. A three way join table is really pretty crazy.