framework: Breaking change in relationships with additional where clauses due to PR #25240

• Laravel Version: 5.6.34 and above
• PHP Version: 7.1.x
• Database Driver & Version: -

Description:

Our tests started failing after https://github.com/laravel/framework/pull/25240 was merged and tagged. This change was first tagged in 5.6.34

The problem we are having is that we are working with a legacy database that has some tables that have a structure that is similar to composite primary keys. As Laravel does not have support for composite primary keys, we worked around this by providing a where on the relationship that would append the second part of the “composite” primary key, like this:

class TestModel extends Model
{
    protected $primaryKey = 'identifier_1';

    public function relatedModel() {
        return $this->hasOne(RelatedModel::class, 'identifier_1', 'identifier_1')
            ->where(['identifier_2', '=', $this->identifier_2]);
    }
}

Then, somewhere later on we fetch a collection of models and then we need to lazy eager load the relationship on one of the models like this:

$collection = TestModel::where('x', '=', 'value')->get();

// ...

$collection->first()->load('relatedModel');

This has worked up until 5.6.33.

Since the change made in https://github.com/laravel/framework/pull/25240, however, this is not possible anymore because a new instance of the TestModel is created, which loses all attributes that were there before.

The $this->identifier_2 in ->where(['identifier_2', '=', $this->identifier_2]); will therefor be null and will return the wrong related model, or no model at all.

This has been reported (with a PR) before: https://github.com/laravel/framework/pull/25296 but this has been closed by the author, yet the breaking change is still present.

Steps To Reproduce:

See: https://github.com/RikSomers/LaravelRelationBug

Clone the repo then run the unit-test.

As is, they will fail because the composer.json will get the latest tag for laravel\framework: "laravel/framework": "5.6.*"

Now, edit the composer.json to fetch laravel\framework version 5.6.33: "laravel/framework": "5.6.33"

Run the tests again, and the tests will pass, proving the breaking change was introduced with Laravel 5.6.34 and above.