27.2. Validator Chains
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## 27.2. Validator Chains

Often multiple validations should be applied to some value in a particular order. The following code demonstrates a way to solve the example from the introduction, where a username must be between 6 and 12 alphanumeric characters:

    <?php
    // Provides validator chaining capability
    require_once 'Zend/Validate.php';

    // Validators needed for the example
    require_once 'Zend/Validate/StringLength.php';
    require_once 'Zend/Validate/Alnum.php';

    // Create a validator chain and add validators to it
    $validatorChain = new Zend_Validate();
    $validatorChain->addValidator(new Zend_Validate_StringLength(6, 12))
                   ->addValidator(new Zend_Validate_Alnum());

    // Validate the username
    if ($validatorChain->isValid($username)) {
        // username passed validation
    } else {
        // username failed validation; print reasons
        foreach ($validatorChain->getMessages() as $message) {
            echo "$message\n";
        }
    }

Validators are run in the order they were added to `Zend_Validate`. In the above example, the username is first checked to ensure that its length is between 6 and 12 characters, and then it is checked to ensure that it contains only alphanumeric characters. The second validation, for alphanumeric characters, is performed regardless of whether the first validation, for length between 6 and 12 characters, succeeds. This means that if both validations fail, `getMessages()` will return failure messages from both validators.

In some cases it makes sense to have a validator break the chain if its validation process fails. `Zend_Validate` supports such use cases with the second parameter to the `addValidator()` method. By setting `$breakChainOnFailure` to `true`, the added validator will break the chain execution upon failure, which avoids running any other validations that are determined to be unnecessary or inappropriate for the situation. If the above example were written as follows, then the alphanumeric validation would not occur if the string length validation fails:

    <?php
    $validatorChain->addValidator(new Zend_Validate_StringLength(6, 12), true)
                   ->addValidator(new Zend_Validate_Alnum());

Any object that implements `Zend_Validate_Interface` may be used in a validator chain.

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