On Mar 5, 2011, at 4:04 PM, Mark Sobkowicz wrote:
> I have a query I'd like to put in a named_scope. I have a model Item and a
> model Rental. Item has_many rentals, Rental has_one item. Rental has a
> boolean field "active". I'd like to make a named scope that finds all the
> items with no active rental.
Can you be more specific about the associations? I suspect what you've got is
actually Rental belongs_to Item (so the 'rentals' table has a field
'item_id')...
Assuming that's the case, the *query* to find the items would look like:
Item.find(:all, :joins => 'OUTER JOIN rentals ON rentals.item_id = items.id AND
rentals.active = 1', :conditions => 'rentals.id IS NULL')
so the corresponding scope (on the Item model) would be:
named_scope :without_active_rentals, :joins => 'OUTER JOIN rentals ON
rentals.item_id = items.id AND rentals.active = 1', :conditions => 'rentals.id
IS NULL'
(this is Rails 2 syntax, conversion to the ARel-style should be straightforward)
---
Note: I was really hoping this would work (in the Item model):
has_many :active_rentals, :class_name => 'Rental', :conditions => { :active =>
true }
then getting the Item.without_active_rentals for free from the automatic scopes
system. (You get without_rentals from that, but it's not quite what's needed).
But it appears that exists_sql_condition doesn't take association conditions
into account. Bummer. :)
--Matt Jones
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