Calling an association through another, without hm:t?

gistfile1.rb

class Order < AR::Base
  has_many :widgets
  has_many :parts, through: :widget
end

class Widget < AR::Base
  has_many :parts
end

class Part < AR::Base
end



puts order.parts.to_sql  # => combined parts from all the widgets in the order

# but what if I've got some Widgets from elsewhere?...


puts Widget.where(color: 'blue').parts.to_sql  # => nope.


Order.transaction do
  o = Order.new
  o.widgets = Widget.where(color: 'blue').to_a
  o.save!
  puts o.parts.to_sql
  raise ActiveRecord::Rollback
end  # => almost what I want, and yet entirely not


puts Part.where(widget_id: Widget.where(color: 'blue')).to_sql
  # => works in this case, but a more complex association is not so easily inverted