[10.x] Add 'makeSearchableUsing' method (to allow eager loading when making specific models searchable)

[gdebrauwer]

In the projects at work, we use Laravel's lazy loading prevention. But when installing and using Scout, I noticed that Scout does not use makeAllSearchableUsing when making specific models searchable (which I thought at first). This causes lazy loading errors when the toSearchableArray method expects certain relations to be loaded (as is the case when importing all models because it then uses the makeAllSearchableUsing method).

public function toSearchableArray() : array
{
    return [
        // This causes lazy loading on every model that is made searchable
        'some_relation_attribute' => $this->someRelation->attribute
    ];
}

$someModels->searchable();
$parentModel->someRelation()->searchable();

So to fix this, I propose introducing a new method: makeSearchableUsing. This method allows you to modify models before the toSearchableArray method is called on each of those models

protected function makeSearchableUsing($models)
{
    // load relations or add extra data that will be used in the "toSearchableArray" method
    return $models->load(...);
}

[taylorotwell]

Can't you just call load on the collection before calling searchable?

[gdebrauwer]

No that does not work when data syncing is queued. And even if it would work, it would be very annoying in my opinion. You might have to make models searchable in different places, which means you have to repeat the eager loading code in all those places.

[taylorotwell]

Why BaseCollection instead of an Eloquent collection? Which one is it? Base collection doesn't have a load method.

[gdebrauwer]

ah indeed it should be an eloquent collection

[mstaack]

this broke my scout setup, had to revert to version before.

see: #736

[nemoitis]

@mstaack Same here. All on a sudden my tests are going red.