Laravel relationships avoid query where foreign key is null - laravel

Question

When eager loading, is it possible to avoid doing an extra query when the foreign key in a relationship is null and therefore does not match any related record? In my example I have a Product and User.
A Product is owned by a User but can also be optionally edited by a User. So my model looks like this:
class Product extends Model
{
public function user()
{
return $this->belongsTo(User::class);
}
public function editor()
{
return $this->belongsTo(User::class, 'editor_id');
}
}
When a product has not been edited, it's editor_id attribute is NULL.
If I hadn't been eager loading I know I could do something like the following:
$product = Product::find(1);
if (!is_null($product->editor_id)) {
// Load the relation
}
However, this isn't an option for me and I would ideally like to avoid an extra, unnecessary query being run when eager loading:
Query: select * from `users` where `users`.`id` in (?)
Bindings: [0]
I was wondering if something similar to the following would be possible?
public function editor()
{
if (!is_null($this->editor_id)) {
return $this->belongsTo(User::class, 'editor_id');
}
}
When doing the above I get this error:
Call to a member function addEagerConstraints() on a non-object
I'm guessing that this is because it's not guaranteed that this method returns a Relation object.
Thanks

Answer 1

I solved this by creating a new Relation subclass that implements the required methods but simply returns null when actually obtaining results:
namespace My\App;
use Illuminate\Database\Eloquent\Collection;
use Illuminate\Database\Eloquent\Relations\Relation;
class NullRelation extends Relation {
public function __construct() {}
public function addConstraints() {}
public function addEagerConstraints(array $models) {}
public function initRelation(array $models, $relation) {}
public function match(array $models, Collection $results, $relation) {
return [];
}
public function getResults() {
return null;
}
}
Then inside your relation method(s) you can check for null and return an instance of NullRelation instead:
public function editor() {
if ($this->editor_id === null) {
return new NullRelation();
} else {
return $this->belongsTo(User::class, 'editor_id');
}
}
It's a bit ugly and you'd be repeating youself a lot, so if I were using this in more than one place I'd probably create a subclass of the Model, then create versions of the belongsTo, hasOne methods and perform the check there:
public function belongsToIfNotNull($related, $foreignKey = null, $otherKey = null, $relation = null) {
if ($this->$foreignKey === null) {
return new NullRelation();
} else {
return parent::belongsTo($related, $foreignKey, $otherKey, $relation);
}
}
Finally in your modal that inherits the new subclass, your relation method simply becomes
public function editor() {
return $this->belongsToIfNotNull(User::class, 'editor_id');
}

Answer 2

Laravel Docs
Querying Relations When Selecting
When accessing the records for a model, you may wish to limit your results based on the existence of a relationship.
$posts= Post::has('editor')->get();
You may also specify an operator and a count:
$posts = Post::has('editor', '>=', 3)->get();