Doing a COUNT(*) GROUP BY based on a ManyToMany relation using DQL? - php

Question

I have two entities Person and Skill, where a Person may have multiple skills.
Person
/**
* #ORM\Entity(repositoryClass="App\Repository\PersonRepository")
*/
class Person
{
/**
* #ORM\Id()
* #ORM\GeneratedValue()
* #ORM\Column(type="integer")
*/
private $id;
/**
* #ORM\ManyToMany(targetEntity="App\Entity\Skill", inversedBy="people")
*/
private $skills = [];
// other fields and getters/setters
}
Skill
<?php
namespace App\Entity;
use Doctrine\ORM\Mapping as ORM;
/**
* #ORM\Entity(repositoryClass="App\Repository\SkillRepository")
*/
class Skill
{
/**
* #ORM\Id()
* #ORM\GeneratedValue()
* #ORM\Column(type="integer")
*/
private $id;
/**
* #ORM\ManyToMany(targetEntity="App\Entity\Person", mappedBy="skills")
*/
private $people = [];
// other fields and getters/setters
}
I have a form where I can filter people by skills, each skill is a checkbox and I want the number of people having that skill along with the checkbox's label.
The result is that:
I got it working using the following native query:
SELECT s.id, COUNT(*) AS c
FROM skill s
JOIN person_skill ps /* table required by the M2M relation between person and skill */
ON s.id = ps.skill_id
GROUP BY s.id
As you can see, I require a JOIN on the ManyToMany table in order to get those counts.
How could I do this using Doctrine's DQL instead of using a native query?

Answer 1

Actually when mapping entities with relations, Doctrine uses a custom object named ArrayCollection.
It comes with many methods, such as filter() and count().
You can add a method to your skill entity if you want that would use the count method of the ArrayCollection (people).
To make sure you use the ArrayCollection properly you'll have to change your Skill class like this:
class Skill
{
/**
* #ORM\Id()
* #ORM\GeneratedValue()
* #ORM\Column(type="integer")
*/
private $id;
/**
* #ORM\ManyToMany(targetEntity="App\Entity\Person", mappedBy="skills")
*/
private $people; //<-- Removed the default array definition
public function __construct()
{
$this->people = new ArrayCollection(); //Add this line in your constructor
}
public function countPeople()
{
return $this->people->count(); //Will return the number of people joined to the skill
}
// other fields and getters/setters
}

Answer 2

Allright, I found the solution:
$rows = $this->_em->createQueryBuilder('s')
->select('s.id, COUNT(p.id) AS c')
->from(Skill::class, 's')
->join('s.people', 'p')
->groupBy('s.id')
->getQuery()
->getArrayResult();
It generates the following query:
SELECT s0_.id AS id_0, COUNT(p1_.id) AS sclr_1
FROM skill s0_
INNER JOIN person_skill p2_
ON s0_.id = p2_.skill_id
INNER JOIN person p1_
ON p1_.id = p2_.person_id
GROUP BY s0_.id