help with join tables and has_and_belongs_to_many

rubyonrails-talk
1

Hi,

I have a user model and a privilege model. They have the has_and_belongs_to_many relationship. Here are the model defs:

class User < ActiveRecord::Base   belongs_to :status   has_and_belongs_to_many :privileges end

class Privilege < ActiveRecord::Base   has_and_belongs_to_many :users end

Now I have a migration script to create the join table and populate a few users with some privileges...

class CreateAndInitPrivileges < ActiveRecord::Migration   def self.up     create_table :privileges_users do |t|       t.column :user_id, :integer, :null => false       t.column :privilege_id, :integer, :null =>false     end

    admin_priv = Privilege.find_by_name('admin')     user_priv = Privilege.find_by_name('user')

    admin_user = User.find_by_email('admin@blah.com')     admin_user.privileges << admin_priv     admin_user.privileges << user_priv

    anon_user = User.find_by_email('anon@blah.com')     anon_user.privileges << user_priv # BOMB HERE

  end

  def self.down     drop_table :privileges_users   end end

The line anon_user.privileges << user_priv bombs because Rails tries to insert a row into privileges_users table with id of 1, but that id is already taken because of the previous admin_user.privileges << admin_priv admin_user.privileges << user_priv calls.

What's going on? Why is Rails not using the next highest id?

Thanks for the help, -- Christopher

2

I do not know the why of it, but I hit it myself a few days ago. Unless you really need that id column in the privileges table, use

   create_table(:privileges_users, :id=>false) do |t|      t.column :user_id, :integer, :null => false      t.column :privilege_id, :integer, :null =>false    end

The table will be created without the id column and your inserts will work.

3

Awesome, that worked perfectly! And to think I was about to turn in for the night... :wink:

Thank you very much.