has_many :through question

rubyonrails-talk
#1

I am trying to setup the has_many :through scheme but am having some
difficulties.

The long story short I am building a simple ACL.
I have Users, Roles and Permissions. Below is what I started with for
associations.

class User < ActiveRecord::Base
  has_and_belongs_to_many :roles
end

class Role < ActiveRecord::Base
has_and_belongs_to_many :users
has_and_belongs_to_many :permissions
end

class Permission < ActiveRecord::Base
has_and_belongs_to_many :roles
end

With this setup, everything was connected together and working fine.
I would like to setup users having permissions through roles.

I tried:
class User < ActiveRecord::Base
  has_and_belongs_to_many :roles
  has_many :permissions, :through => :roles
end

but that does not work. From what I have read, if I can get the
through to work, I should beable to do something like
@user.permissions.

How can I set this up so a user can have many roles, a role can have
many permissions, a role can have many users, and a user can have
permissions through roles?

Any suggestions would be very helpful.

#2

has_many :through only works though another has_many, not a habtm. In
order get a list of a users permissions, you'll need to loop through
their roles and collect all the permissions.

Unless you're planning on multiple installs of your app each with
different permission requirements, you probably don't actually need to
store permissions in the DB. If that's the case, you might want to check
out the GateKeeper plugin ( http://gatekeeper.rubyforge.org/ ).

jm wrote:

#3

Should I use this instead?

class User < ActiveRecord::Base
  has_many :roles
  has_many :permissions, :through => :roles
end

class Permission < ActiveRecord::Base
  has_many :roles
  has_many :users, :through => :roles
end

class Role < ActiveRecord::Base
  belongs_to :user
  belongs_to :permission
end