empty? on associations
Reported by Chris Wanstrath | 2007-09-18 12:41:24 UTC
Nicolas wants:
class Provider < AR
has_many :orders
end
class Order < AR
belongs_to :provider
end
Provider.select { |p| p.name =~ 'A%' && p.orders.empty? }
(to retrieve all the providers which name begins by A and have no orders)
Mislav says:
SELECT ... FROM providers
LEFT JOIN orders ON provider.id = orders.provider_id
WHERE providers.name LIKE 'A%'
GROUP BY providers.id
HAVING COUNT(orders.id ) = 0
Comments and changes to this ticket
-
ronin-13570 (at lighthouseapp) 2008-02-15 03:19:55 UTC
Unfortunately this won't work as suggested as the GROUP BY clause MUST include every non aggregating column listed in the SELECT clause.
Typically the same thing can be achieved using a correlated sub-query (and NOT EXIST) which most databases can optimise to essentially the same thing anyway.
-
Chris Wanstrath 2008-02-16 03:30:58 UTC
- State changed from “open” to “hold”
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Chris Wanstrath