You should never trust the data received from users. To validate a model with user inputs, you should call yiibaseModel::validate() method. It returns a Boolean value if the validation succeeds. If there are errors, you may get them from the yiibaseModel::$errors property.

Using Rules

To make the validate() function work, you should override the yiibaseModel::rules() method.

Step 1 − The rules() method returns an array in the following format.

[
   // required, specifies which attributes should be validated
   [''attr1'', ''attr2'', ...],
   // required, specifies the type a rule.
   ''type_of_rule'',
   // optional, defines in which scenario(s) this rule should be applied
   ''on'' => [''scenario1'', ''scenario2'', ...],
   // optional, defines additional configurations
   ''property'' => ''value'', ...
]

For each rule, you should define at least which attributes the rule applies to and the type of rule applied.

The core validation rules are − boolean, captcha, compare, date, default, double, each, email, exist, file, filter, image, ip, in, integer, match, number, required, safe, string, trim, unique, url.

Step 2 − Create a new model in the models folder.

<?php
   namespace appmodels;
   use Yii;
   use yiibaseModel;
   class RegistrationForm extends Model {
      public $username;
      public $password;
      public $email;
      public $country;
      public $city;
      public $phone;
      public function rules() {
         return [
            // the username, password, email, country, city, and phone attributes are
            //required
            [[''username'' ,''password'', ''email'', ''country'', ''city'', ''phone''], ''required''],
            // the email attribute should be a valid email address
            [''email'', ''email''],
         ];
      }
   }
?>

We have declared the model for the registration form. The model has five properties − username, password, email, country, city, and phone. They are all required and the email property must be a valid email address.

Step 3 − Add the actionRegistration method to the SiteController where we create a new RegistrationForm model and pass it to a view.

public function actionRegistration() {
   $model = new RegistrationForm();
   return $this->render(''registration'', [''model'' => $model]);
}

Step 4 − Add a view for our registration form. Inside the views/site folder, create a file called registration.php with the following code.

<?php
   use yiibootstrapActiveForm;
   use yiibootstrapHtml;
?>

<div class = "row">
   <div class = "col-lg-5">
      <?php $form = ActiveForm::begin([''id'' => ''registration-form'']); ?>
         <?= $form->field($model, ''username'') ?>
         <?= $form->field($model, ''password'')->passwordInput() ?>
         <?= $form->field($model, ''email'')->input(''email'') ?>
         <?= $form->field($model, ''country'') ?>
         <?= $form->field($model, ''city'') ?>
         <?= $form->field($model, ''phone'') ?>
         <div class = "form-group">
            <?= Html::submitButton(''Submit'', [''class'' => ''btn btn-primary'',
               ''name'' => ''registration-button'']) ?>
         </div>
      <?php ActiveForm::end(); ?>
   </div>
</div>

We are using the ActiveForm widget for displaying our registration form.

Step 5 − If you go to the local host http://localhost:8080/index.php?r=site/registration and click the submit button, you will see validation rules in action.

Step 6 − To customize the error message for the username property, modify the rules() method of the RegistrationForm in the following way.

public function rules() {
   return [
      // the username, password, email, country, city, and phone attributes are required
      [[''password'', ''email'', ''country'', ''city'', ''phone''], ''required''],
      [''username'', ''required'', ''message'' => ''Username is required''],
      // the email attribute should be a valid email address
      [''email'', ''email''],
   ];
}

Step 7 − Go to the local host http://localhost:8080/index.php?r=site/registration and click the submit button. You will notice that the error message of the username property has changed.

Step 8 − To customize the validation process, you may override these methods.

• yiibaseModel::beforeValidate(): triggers a

  yiibaseModel::EVENT_BEFORE_VALIDATE event.

• yiibaseModel::afterValidate(): triggers a

  yiibaseModel::EVENT_AFTER_VALIDATE event.

Step 9 − To trim the spaces around the country property and turn empty input of the city property into a null, you may the trim and default validators.

public function rules() {
   return [
      // the username, password, email, country, city, and phone attributes are required
      [[''password'', ''email'', ''country'', ''city'', ''phone''], ''required''],
      [''username'', ''required'', ''message'' => ''Username is required''],
      [''country'', ''trim''],
      [''city'', ''default''],
      // the email attribute should be a valid email address
      [''email'', ''email''],
   ];
}

Step 10 − If an input is empty, you can set a default value for it.

public function rules() {
   return [
      [''city'', ''default'', ''value'' => ''Paris''],
   ];
}

If the city property is empty, then the default “Paris” value will be used.