Миграции:
 
class CreateBrandsTable extends Migration
{
    public function up()
    {
        Schema::create('brands', function (Blueprint $t) {
 
            $t->increments('id');
 
            $t->string('name')->index();
 
            $t->timestamps();
            $t->softDeletes();
        });
    }
 
    public function down()
    {
         Schema::dropIfExists('brands');
    }
}
 
 
class CreateEditionsTable extends Migration
{
    public function up()
    {
        Schema::create('editions', function (Blueprint $t) {
            
            $t->increments('id');
 
            $t->integer('brand_id')->index(); 
            $t->foreign('brand_id')->references('id')->on('brands')->onDelete('cascade');
 
            $t->string('name')->index();
 
            $t->string('slug')->nullable()->index();
            $t->text('body')->nullable();
 
            $t->timestamps();
            $t->softDeletes();
        });
    }
 
    public function down()
    {
        Schema::dropIfExists('editions');
    }
}
 
Модели:
 
<?php
 
namespace App\Entity\Vehicle;
 
use App\Entity\Behaviors\ImagePublicBehavior;
use App\Entity\brand\BrandComment;
use App\Entity\User;
use Cviebrock\EloquentSluggable\Sluggable;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\SoftDeletes;
use Illuminate\Notifications\Notifiable;
 
class Brand extends Model
{
    use Notifiable;
    use SoftDeletes;
    use Sluggable;
    use ImagePublicBehavior;
 
    protected $dates = ['created_at','updated_at', 'deleted_at'];
 
    protected $fillable = [
        'name',
        'slug',
        'parent_id',
    ];
    
    ...
    
    public function editions()
    {
        return $this->hasMany(Edition::class,  'id', 'brand_id');
    }
 
    ...
}
 
?>
 
 
class EditionSerial extends Model
{
    use Notifiable;
    use SoftDeletes;
    use Sluggable;
    use ImagePublicBehavior;
 
    protected $table = 'editions';
 
    protected $dates = ['created_at','updated_at', 'deleted_at'];
 
    protected $visible = ['id', 'name'];
 
    protected $fillable = [
        'name',
        'brand_id',
    ];
 
    public function sluggable()
    {
        return [
            'slug' => ['source' => 'name']
        ];
    }
 
    
    public function brand()
    {
        return $this->belongsTo(Brand::class, 'brand_id', 'id');
    }
}
 
 
Контроллер (!!! проблема): 
 
 
namespace App\Http\Controllers\Admin\Vehicles;
 
use App\Entity\Vehicle\Brand;
use App\Entity\Vehicle\EditionSerial;
use App\Entity\Vehicle\Vehicle;
use App\Http\Controllers\Controller;
use App\Http\Requests\Admin\Vehicle\BrandRequest;
 
class BrandsController extends Controller
{
    public function show(Brand $brand)
    {
         $brand->editions()->create(['name' => 'Example-xx']);
 
        // Всегда 0, зотя записи в таблицах есть
        echo $brand->editions()->count();
 
        // так работает
        // EditionSerial::create(['name' => 'xxx', 'brand_id'=>$brand->id]);
 
        return view('brands.admin.show', compact('brand','editions'));
 
    }
}