How do you scope ActiveRecord associations in Rails 3?

Question

I have a Rails 3 project. With Rails 3 came Arel and the ability to reuse one scope to build another. I am wondering if there is a way to use scopes when defining a relationship (e.g. a "has_many").

I have records which have permission columns. I would like to build a default_scope that takes my permission columns into consideration so that records (even those accessed through a relationship) are filtered.

Presently, in Rails 3, default_scope (including patches I've found) don't provide a workable means of passing a proc (which I need for late variable binding). Is it possible to define a has_many into which a named scope can be passed?

The idea of reusing a named scope would look like:

Orders.scope :my_orders, lambda{where(:user_id => User.current_user.id)}
has_many :orders, :scope => Orders.my_orders

Or implicitly coding that named scope in the relationship would look like:

has_many :orders, :scope => lambda{where(:user_id => User.current_user.id)}

I'm simply trying to apply default_scope with late binding. I would prefer to use an Arel approach (if there is one), but would use any workable option.

Since I am referring to the current user, I cannot rely on conditions that aren't evaluated at the last possible moment, such as:

has_many :orders, :conditions => ["user_id = ?", User.current_user.id]

Answer 1

I suggest you take a look at "Named scopes are dead"

The author explains there how powerful Arel is :)

I hope it'll help.

Answer 2

I use something like:

class Invoice << ActiveRecord::Base

scope :aged_0,  lambda{ where("created_at IS NULL OR created_at < ?", Date.today + 30.days).joins(:owner) }

end

Answer 3

Instead of scopes I've just been defining class-methods, which has been working great

def self.age0 do where("blah") end