Retrieving records that have a minimal number of related records

Question

There is one-2-many relation between Property and Reservation. Property has column called 'nr_of_bookings'. I need DQL that will retrieve only the properties that has COUNT(Reservation) less than Property.nr_of_bookins.

An example: Some Property has nr_of_bookings = 3 . If it has 5 Reservations related, it will not be retrieved. But if it has 2 related Reservations, it will be retrieved.

I tried numerous combinations, but I miss something obviosly. I posted similar question here , but it is better to start from scratch. Thanks.

Answer 1

Have you tried:

'SELECT p FROM Product p WHERE SIZE(p.reservations) < p.nr_of_bookings'

EDIT: The above is for Doctrine 2. For Doctrine 1.2, looking at your code, I'm guessing your HAVING clause is referencing something that's not in a group by or the result of an aggregate function. Try something like this:

$q = PropertyTable::getInstance()
    ->createQuery('p') 
    ->select('p.*, COUNT(r.id) as num_of_reservations, SUM(p.nr_of_bookings) as num_bookings') 
    ->leftJoin('p.Reservation r') 
    ->groupBy('p.id') 
    ->having('num_of_reservations < num_bookings');

You're grouping by p.id so SUM(p.nr_of_bookings) will be equal to p.nr_bookings.

From the MySQL documentation:

The SQL standard does not permit the HAVING clause to name any column not found in the GROUP BY clause if it is not enclosed in an aggregate function.