基于has_one：through关系在Rails 3中创建作用域

Question

Rails 3.0.3 and Ruby 1.9.2

I have the following class

class item < ActiveRecord::Base
  belongs_to :user
  has_one :country, :through => :user

  ..

end

So itemA.country yields "United States"

The question is how do I created a (named) scope for all items owned by US users

When I try something like:

scope :american, where('countries.name' => 'United States').includes([:user, :country])

then Item.american keeps coming back empty even when Item.first.country => 'United States'

Incidentally, in the Rails 2.3.4 version we had:

named_scope :american, :include => {:user, :country}, :conditions => { 'countries.printable_name' => 'United States' }

And that worked as advertised.

Answer 1

You forgot to pluralize the table names, I also think the ordering of include and where may matter. It's also recommended to use a join instead when specifying conditions on associations like so:

scope :american, joins(:users, :countries).where('countries.name' => 'United States')

If you'd prefer to still use includes:

scope :american, includes(:users, :countries).where('countries.name' => 'United States')