Traits

Traits are a powerful feature in PHP that allow developers to reuse sets of methods in multiple classes without relying on traditional inheritance. In languages with single inheritance (like PHP), a class can only inherit from one parent class. This can sometimes be limiting when you want to share functionality across multiple, unrelated classes. Traits solve this problem by letting you "mix in" methods into different classes.

Disallowing Just Spaces

For some reason, 'notEmptyString' does not prevent an input string from being simply spaces. e.g. '  ' So we need an additional rule to check for that.

  $validator
    ->notEmptyString('name')
    ->add('name', 'notSpaces', [
      'rule' => function ($value, $context) {
        return trim($value) !== '';
      },
      'message' => 'Name cannot be just spaces.',
    ]);

Using Traits

Instead of adding that validation rule individually to every field that needs it, you can use a Trait and simply call it once per Model class.

Create the Trait at /src/Model/Validation/CommonValidationTrait.php

<?php
namespace App\Model\Validation;

trait CommonValidationTrait
{
  use Cake\Validation\Validator;
  
  public function applyNotSpacesRules(Validator $validator, array $fields)
  {
    foreach ($fields as $field) {
        $validator->add($field, 'notSpaces', [
            'rule' => function ($value, $context) {
                return trim($value) !== '';
            },
            'message' => str_replace('_', ' ', ucfirst($field)) . ' cannot be just spaces.',
        ]);
    }
    return $validator;
  }
}

Then in each of your Table Models add the following lines to utilize the Trait you just made. This example is for /src/Model/Table/UsersTable.php

<?php
...
use App\Model\Validation\CommonValidationTrait;

class UsersTable extends Table
{
  use CommonValidationTrait;
  ...
  $this->applyNotSpacesRules($validator, ['username', 'first_name', 'last_name']);
  return $validator;
}