How to fetch row count of related entities? - symfony

Question

I have two entities, Class and Student. One Class can have multiple Students (oneToMany):
# YAML notation for Entity 'Class'
...
oneToMany:
students:
targetEntity: MyBundle\Entity\Student
mappedBy: class
For fetching all Classes, I'm writing my own query like this:
SELECT c
FROM MyBundle:Class c
WHERE c.whatever = :parameter
ORDER BY c.id DESC
Now I'm trying to fetch a list of Classes, ordered (DESC) by the count of related Students. So that the result would look like:
Class.id Class.count(Student)
-------- --------------------
3 109
1 81
4 58
2 21
How would I go there? I tried something somewhat like this:
SELECT
c,
COUNT(c.students) AS students
FROM MyBundle:Class c
WHERE c.whatever = :param
GROUP BY c.id
ORDER BY students DESC
(Note: I implement DoctrineExtensions' Date function)
But I'm getting an error:
[Semantical Error] line 0, col 26 near 'students)': Error: Invalid PathExpression. StateFieldPathExpression or SingleValuedAssociationField expected.

Answer 1

Try to use this in your Class repository:
public function getAllClassesOrderedByNumberOfStudents()
{
$qb = $this->createQueryBuilder('class');
$buffer = $qb
->select('class, COUNT(students) AS students_per_class')
->innerJoin('class.students', 'students')
->groupBy('class.id')
->orderBy('students_per_class', 'DESC');
$q = $buffer->getQuery();
return $q->getResult();
}