How can I do a find in Rails with conditions set on the join table of a :through association?

Question

I have the following models:

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

class Task < ActiveRecord::Base
  has_many :permissions
  has_many :users, :through => :permissions

class Permission < ActiveRecord::Base
  belongs_to :task
  belongs_to :user

I want to be able to display only tasks which a user has access to (i.e., the read flag is set to true in the Permissions table). I can accomplish this with the following query, but it doesn't seem very Rails-y to me:

@user = current_user
@tasks = @user.tasks.find_by_sql(["SELECT * FROM tasks INNER JOIN permissions ON tasks.id = permissions.task_id WHERE permissions.read = true AND permissions.user_id = ?", @user.id])

Anyone know the right way to do this?

Answer 1

Sorry, this is quick guess. sorry if this isn't right.

@user.tasks.find(:all, :conditions => "permissions.read = 'true' ")

Answer 2

Answering my own question here, Rails actually lets you set conditions on the association itself. So, e.g., in my User model, I'd modify that has_many association to be:

has_many :tasks, :through => :permissions, :conditions => 'permissions.read = true'

Pretty neat. The solution suggested by Trip also works (except that, for MySQL at least, 'true' should not be quoted). I swear I tried that one...!