There are three ways to add custom validation rules in Laravel: using closures, Rule classes, and form requests. 1. Use closures to be suitable for lightweight verification, such as preventing the username "admin"; 2. Create Rule classes (such as ValidUsernameRule) to make complex logic clearer and maintainable; 3. Integrate multiple rules in form requests and centrally manage verification logic. At the same time, you can set prompts through custom messages methods or incoming error message arrays to improve flexibility and maintainability.

Adding custom validation rules to your Laravel project is a key step to improve form processing flexibility and accuracy. Although the default verification rules are practical, they are often not enough when facing complex business logic, so we need to customize them ourselves.

How to create a basic custom validation rule

Laravel provides a variety of ways to implement custom verification logic, most commonly using Validator::make or using the Artisan command to generate Rule objects. You can start like this:

 use Illuminate\Support\Facades\Validator;

$validator = Validator::make($request->all(), [
    'username' => ['required', 'string', function ($attribute, $value, $fail) {
        if (strtolower($value) === 'admin') {
            $fail('The '.$attribute.' cannot be "admin".');
        }
    }],
]);

The closure in this code is a simple custom rule that prevents the username from being "admin". This method is suitable for temporary and lightweight verification needs.

Use Rule class to make verification clearer and more maintainable

For more complex verification logic, it is recommended to use the Rule class. Execute the following Artisan command to generate a rule class file:

• php artisan make:rule ValidUsernameRule

After that, you will find the corresponding class in app/Rules/ directory. Open this file and write your judgment logic in the passes method, such as checking whether the user name contains sensitive words or format errors.

 public function passes($attribute, $value)
{
    return strtolower($value) !== 'admin';
}

Then use it in the form request or controller:

 use App\Rules\ValidUsernameRule;

$request->validate([
    'username' => ['required', new ValidUsernameRule],
]);

This structure is clearer and easier to test and reuse.

Integrate multiple custom rules in form requests

If you have a complex form that requires multiple custom rules, it is recommended to use "Form Request". After creating it through the command php artisan make:request StoreUserRequest , refer to the Rule class you defined in rules() method, or write a closure directly in it.

 public function rules()
{
    Return [
        'username' => ['required', new ValidUsernameRule],
        'email' => [
            'required',
            'email',
            function ($attribute, $value, $fail) {
                if (strpos($value, 'example.com') === false) {
                    $fail('Email must be from example.com domain.');
                }
            }
        ]
    ];
}

The advantage of this is to centralize all verification logic in one place to manage it, avoiding the controller bloated and facilitate subsequent maintenance.

Tips for customizing error message

In addition to the rules themselves, prompts are also important. The second parameter can be passed into the validator to specify the error message:

 $messages = [
    'username.required' => 'Please choose a username.',
    'username.ValidUsernameRule' => 'That username is not allowed.',
];

Validator::make($request->all(), $rules, $messages);

If it is a form request, you can directly override messages() method to return these prompts.

Basically these methods. The rational use of closures, Rule classes, and form requests can make custom verification both powerful and concise.

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