Find the latest plants by category doctrine - symfony

Question

How to get the latest plants by category, ManyToMany relationship, using doctrine can help me I'm struggling a lot
Entity Plant
Entity plant_category
Entity category
$sql = "SELECT category_id, c.name, c.slug, i.name
FROM category AS c
LEFT JOIN plant_category AS pc
ON pc.category_id = c.id
INNER JOIN (SELECT id, name FROM plant
ORDER BY id DESC LIMIT 1) AS i
ON pc.plant_id = i.id
GROUP BY c.id, c.id, i.name
ORDER BY c.id ASC";
I did a search but I couldn't find anything yet with doctrine
$t = $this->createQueryBuilder("c")
->select("c")
->from(Plant::class, "p")
->leftJoin('p.categories', 'cc')
->leftJoin('(SELECT id, name FROM plant
ORDER BY id DESC LIMIT 1)
ON pc.plant_id = i.id', "i");

Answer 1

Doctrine ORM works a bit differently than working with a standard SQL query.
To work with the entities, the separation of concerns changes from an abstraction (non-deterministic array) to a static model (deterministic object).
In that your Category entity is expected to have an association for the i.name column of your query for the desired end-result, otherwise a partial object is implicated, which is highly discouraged due it causing an invalid state of the entity.
You're attempting to solve for a special circumstance where you want to show a single specific record from the ManyToMany association of the Category::$plants collection, which goes against the Object Model design pattern. The object models are expected to be Valid at all times, so accounting for those special circumstances from the context of the ORM breaks that core principal.
In short, the ORM should not be doing that, you're most likely looking for an array result (as given in the answer by #JeanCapelle) or a native query.
Criteria on the Object Model
The simplest workaround is to utilize the object model with a criteria applied to the collection to filter the results and obtain the desired results. However, the use of criteria on the model is also highly discouraged as it heavily impacts performance and has implications of an invalid entity state.
use Doctrine\Common\Collections\Criteria;
class Category
{
/**
* #return Collection|Plants[]
*/
private $plants;
public function __construct()
{
// ...
$this->plants = new ArrayCollection();
}
public function getPlants(): Collection
{
return $this->plants;
}
public function getLatestPlant(): ?Plant
{
$criteria = Criteria::create()->setMaxResults(1);
return $this->plants->matching($criteria->orderBy(['id', 'DESC']))->first() ? : null;
}
}
Then the query would be changed to the following.
$qb = $this->_em->createQueryBuilder();
$t = $qb->select('c')
->from(Category::class, 'c')
->addSelect('p')
->leftJoin('c.plants', 'p')
->orderBy('c.id', 'ASC');
$categories = $t->getQuery()->getResult();
foreach ($categories as $category) {
$latestPlant = $category->getLatestPlant();
echo $latestPlant->getName();
}
Object Model Association on Latest
The more favorable solution considered best-practice, would be to add the foreign key association to the Category table and a ManyToOne relationship on the Category Entity, instead of relying on a subquery to filter from the association. Where the latest plant is maintained through the application and the object model lifecycle.
Category table: id, name, description, slug, latest_plant
class Category
{
/**
* #return Collection|Plants[]
*/
private $plants;
/**
* #return null|Plant
* #ORM\ManyToOne(targetEntity=Plant::class)
* #ORM\JoinColumn(name="latest_plant", referencedColumnName="id", nullable=true)
*/
private ?Plant $latestPlant = null;
public function getPlants(): Collection
{
return $this->plants;
}
// simple example on how to maintain relationship
public function addPlant(Plant $plant)
{
if (!$this->plants->contains($plant)) {
$this->plants->add($plant);
$plant->addCategory($this);
$this->setLatestPlant($this->plants->last() ?: null);
}
}
// simple example on how to maintain relationship
public function removePlant(Plant $plant)
{
if ($this->plants->contains($plant)) {
$this->plants->removeElement($plant);
$plant->removeCategory($this);
if ($this->latestPlant && $this->latestPlant->getId() === $plant->getId()) {
$this->setLatestPlant($this->plants->last() ?: null);
}
}
}
public function getLatestPlant(): ?Plant
{
return $this->latestPlant;
}
public function setLatestPlant(?Plant $plant)
{
$this->latestPlant = $plant;
}
}
Then the query would look like the below.
$qb = $this->_em->createQueryBuilder();
$t = $qb->select('c')
->from(Category::class, 'c')
->addSelect('lp')
->leftJoin('c.latestPlant', 'lp') // Category::$latestPlant
->orderBy('c.id', 'ASC');
$categories = $t->getQuery()->getResult();
foreach ($categories as $category) {
$latestPlant = $category->getLatestPlant();
echo $latestPlant->getName();
}

Answer 2

If your SQL querie is what you expect, I'll suggest you to try something like :
$qb->select('c.id AS category_id', 'c.name', 'c.slug', 'i.name')
->from('Category', 'c')
->leftJoin('c.plantCategories', 'pc')
->innerJoin(
'(SELECT p.id, p.name FROM Plant p ORDER BY p.id DESC LIMIT 1)',
'i',
Join::WITH,
'pc.plant = i.id'
)
->groupBy('c.id', 'c.name', 'c.slug', 'i.name')
->orderBy('c.id', 'ASC');
$results = $qb->getQuery()->getResult();