ImagesTable.php

<?php
namespace App\Model\Table;

use Cake\ORM\Query;
use Cake\ORM\RulesChecker;
use Cake\ORM\Table;
use Cake\Validation\Validator;

class ImagesTable extends Table
{

    public function initialize(array $config)
    {
        parent::initialize($config);

        $this->setTable('images');
        $this->setDisplayField('id');
        $this->setPrimaryKey('id');

        $this->addBehavior('Timestamp');

        $this->belongsTo('Products', [
            'foreignKey' => 'product_id',
            'joinType' => 'INNER',
            'cascadeCallbacks' => true
        ]);

        $this->addBehavior('Xety/Cake3Upload.Upload', [
            'fields' => [
                'url' => [
                    'path' => 'upload/images/:md5'
                ]
            ]
        ]);
    }

    public function validationDefault(Validator $validator)
    {
        $validator
            ->integer('id')
            ->allowEmpty('id', 'create');

        $validator
            ->allowEmpty('url');

        return $validator;
    }

    public function buildRules(RulesChecker $rules)
    {
        $rules->add($rules->existsIn(['product_id'], 'Products'));
        return $rules;
    }

    public function afterDelete($event)
    {
        $file = new File(WWW_ROOT . $event->data['entity']['url']);
        $file->delete();
    }
}