[5.5] Make pivot model instantiable

[BertvanHoekelen]

I was facing the same problems as described in #17770.

When I added a hasOne relation to the pivot model, it was not able to construct the pivot instance on the inverse side of the relation. This PR makes the pivot model behave more like a regular model so it can be instantiated without the need of the pivot attributes.

[taylorotwell]

Paste an entire example of how to recreate this in Laravel.

[BertvanHoekelen]

See http://github.com/bertvanhoekelen/pivot-model-example.

This test will throw the following exception:

Too few arguments to function Illuminate\Database\Eloquent\Relations\Pivot::__construct(), 0 passed in laravel/framework/src/Illuminate/Database/Eloquent/Concerns/HasRelationships.php on line 506 and at least 3 expected

City.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class City extends Model
{
    protected $guarded = [];

    public function products()
    {
        return $this->belongsToMany(Product::class)->withPivot(['id'])->using(CityProduct::class);
    }
}

Product.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Product extends Model
{
    protected $guarded = [];

    public function cities()
    {
        return $this->belongsToMany(City::class)->withPivot(['id'])->using(CityProduct::class);
    }
}

CityProduct.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Relations\Pivot;

class CityProduct extends Pivot
{
    public function city()
    {
        return $this->belongsTo(City::class);
    }

    public function product()
    {
        return $this->belongsTo(Product::class);
    }

    public function order()
    {
        return $this->hasOne(Order::class);
    }
}

Order.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;

class Order extends Model
{
    protected $guarded = [];

    public function cityProduct()
    {
        return $this->belongsTo(CityProduct::class);
    }
}

PivotModelIsNotInstantiableTest.php

<?php

namespace Tests\Unit;

use App\City;
use App\Order;
use App\Product;
use Tests\TestCase;
use Illuminate\Foundation\Testing\DatabaseMigrations;

class PivotModelIsNotInstantiableTest extends TestCase
{
    use DatabaseMigrations;

    /** @test */
    public function pivot_model_is_not_instantiable()
    {
        $city = City::create(['name' => 'Amsterdam']);
        $product = Product::create(['name' => 'Burger']);
        $city->products()->attach($product->id);

        $cityProduct = $city->products()->first()->pivot;

        $order = Order::create(['city_product_id' => $cityProduct->id]);

        $this->assertEquals($cityProduct->id, $order->cityProduct->id);
    }
}

[taylorotwell]

Thanks

[Raulebc]

This way to make relationship is working? or there is other way?

[mazyvan]

I'm facing this problem right now. I love its solved, but I'm using 5.4 dammit