Convert Eloquent HasMany relationship to a HasOne? - eloquent

Question

Ok, i have model A that is linked to many model B, so model A have a hasMany relationship to model B and model B has a belongsTo relationship to model A.
But, amongst all those B there is a particular one, e.g. the one with the higher value, that i want model A to have a dedicated relationship with.
I know i can create a second relationship in model A that re-use the old one and add all the scopes and condition i want, but since i'm building this new relationship from a hasMany, it will return always, no matter what, a collection of results.
Is there a way to have it return a single result instead than a collection? I know i can add a first(), but this involve in using this new relationship as a function, i.e. always with parenthesis, and if possible i would like to still use it the eloquent way.
Is it possible to do that? if yes, how?

Answer 1

How about this:
public function Bs()
{
return $this->hasMany(B::class);
}
public function B()
{
$builder = $this->Bs()->latest(); // Add your own conditions etc...
$relation = new HasOne($builder->getQuery(), $this, 'a_id', 'id');
return $relation; // or return $relation->withDefault();
}
Update:
A new one-of-many relationship shipped with Laravel 8.42. You probably want to use this instead:
public function B(): HasOne
{
return $this->hasOne(B::class)->latestOfMany();
}

Answer 2

Not really no. You have 2 models mapping tables with some attributes as follow
+-----+-----+
| A | B |
+-----+-----+
| id | id |
| ... | a_id|
| | ... |
+-----+-----+
When you call onto the hasMany relationship, the builder executes a query. Something like
SELECT * FROM `B` WHERE `B`.`a_id` = ?
If you make a different relationship for it, you will only duplicate the query (if you load both relationships). You could make an accessor, or just use first().
EDIT Accessor code:
# A model
public function getXAttribute()
{
// Query only if necessary
if(!this->relationLoaded('b')) $this->load('b');
// Use Collection methods to filter
return $this->b->firstWhere(...);
}