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

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开发者_JS百科(["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?

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...!

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

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