empty? on associations

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