BelongsTo relation with nullable relations

[pionl]

• Laravel Version: 9.13.0
• PHP Version: 8.1.2

Description:

• While using belongsTo relations (with/load) there can be situations when there are no relations (nullable relations) to be loaded and query is "invalid". -> select `id`, `name`, `public_name` from `options` where 0 = 1 .
• This similar issue can be potentially found on other relations
• This bug is not noticeable if the results contains at least 1 value in the relation (if you have pagination, some pages can contain this error).

Steps To Reproduce:

1. Create a table with optional belongsTo relations
2. Build a query to get the results (all results should contain null)
3. Here a screenshot of a real queries

Fix

1. In Illuminate\Database\Eloquent\Relations\Relation add property protected bool $hasValidConstrains = true;
2. Change the implementation of Illuminate\Database\Eloquent\Relations\Relation::getEager

 public function getEager()
    {
        if ($this->hasValidConstrains) {
            return $this->get();
        }
        return new Collection();
    }

3. Change the implementation of Illuminate\Database\Eloquent\Relations\BelongsTo::addEagerConstraints

public function addEagerConstraints(array $models)
    {
        // We'll grab the primary key name of the related models since it could be set to
        // a non-standard name and not "id". We will then construct the constraint for
        // our eagerly loading query so it returns the proper models from execution.
        $key = $this->related->getTable().'.'.$this->ownerKey;

        $whereIn = $this->whereInMethod($this->related, $this->ownerKey);

        $eagerModelKeys = $this->getEagerModelKeys($models);

        if ($eagerModelKeys === []) {
            $this->hasValidConstrains = false;
            return;
        }

        $this->query->{$whereIn}($key, $eagerModelKeys);
    }

Result

I can make PR if you consider this a bug (which I believe it is) and don't have the time to make the fix.

Thank you for your time.
Martin.

[driesvints]

I personally don't see a big issue here but you're free to attempt that PR if you like 👍

[pionl]

Hey @driesvints what do you mean? This triggers a query on database that is not needed. I see it as a bug right?

I'll make the PR.