Writing Validators

zend-validator supplies a set of commonly needed validators, but many applications have needs for custom validators. The component allows this via implementations of Zend\Validator\ValidatorInterface.

Zend\Validator\ValidatorInterface defines two methods: isValid() and getMessages(). An object that implements the interface may be added to a validator chain using Zend\Validator\ValidatorChain::addValidator(). Such objects may also be used with zend-inputfilter.

Validators will return a boolean value from isValid(), and report information regarding why a value failed validation via getMessages(). The availability of the reasons for validation failures may be valuable to an application for various purposes, such as providing statistics for usability analysis.

Basic validation failure message functionality is implemented in Zend\Validator\AbstractValidator, which you may extend for your custom validators. Extending class you would implement the isValid() method logic and define the message variables and message templates that correspond to the types of validation failures that can occur. If a value fails your validation tests, then isValid() should return false. If the value passes your validation tests, then isValid() should return true.

In general, the isValid() method should not throw any exceptions, except where it is impossible to determine whether or not the input value is valid. A few examples of reasonable cases for throwing an exception might be if a file cannot be opened, an LDAP server could not be contacted, or a database connection is unavailable, where such a thing may be required for validation success or failure to be determined.

Creating a Validation Class

The following example demonstrates how a custom validator might be written. In this case, the validator tests that a value is a floating point value.

namespace MyValid;

use Zend\Validator\AbstractValidator;

class Float extends AbstractValidator
{
    const FLOAT = 'float';

    protected $messageTemplates = [
        self::FLOAT => "'%value%' is not a floating point value",
    ];

    public function isValid($value)
    {
        $this->setValue($value);

        if (! is_float($value)) {
            $this->error(self::FLOAT);
            return false;
        }

        return true;
    }
}

The class defines a template for its single validation failure message, which includes the built-in magic parameter, %value%. The call to setValue() prepares the object to insert the tested value into the failure message automatically, should the value fail validation. The call to error() tracks a reason for validation failure. Since this class only defines one failure message, it is not necessary to provide error() with the name of the failure message template.

Writing a Validation Class having Dependent Conditions

The following example demonstrates a more complex set of validation rules:

An input value would fail validation for exactly one of the following reasons:

These validation failure reasons are then translated to definitions in the class:

namespace MyValid;

use Zend\Validator\AbstractValidator;

class NumericBetween extends AbstractValidator
{
    const MSG_NUMERIC = 'msgNumeric';
    const MSG_MINIMUM = 'msgMinimum';
    const MSG_MAXIMUM = 'msgMaximum';

    public $minimum = 0;
    public $maximum = 100;

    protected $messageVariables = [
        'min' => 'minimum',
        'max' => 'maximum',
    ];

    protected $messageTemplates = [
        self::MSG_NUMERIC => "'%value%' is not numeric",
        self::MSG_MINIMUM => "'%value%' must be at least '%min%'",
        self::MSG_MAXIMUM => "'%value%' must be no more than '%max%'",
    ];

    public function isValid($value)
    {
        $this->setValue($value);

        if (! is_numeric($value)) {
            $this->error(self::MSG_NUMERIC);
            return false;
        }

        if ($value < $this->minimum) {
            $this->error(self::MSG_MINIMUM);
            return false;
        }

        if ($value > $this->maximum) {
            $this->error(self::MSG_MAXIMUM);
            return false;
        }

        return true;
    }
}

The public properties $minimum and $maximum have been established to provide the minimum and maximum boundaries, respectively, for a value to successfully validate. The class also defines two message variables that correspond to the public properties and allow min and max to be used in message templates as magic parameters, just as with value.

Note that if any one of the validation checks in isValid() fails, an appropriate failure message is prepared, and the method immediately returns false. These validation rules are therefore sequentially dependent; that is, if one test should fail, there is no need to test any subsequent validation rules. This need not be the case, however. The following example illustrates how to write a class having independent validation rules, where the validation object may return multiple reasons why a particular validation attempt failed.

Validation with Independent Conditions, Multiple Reasons for Failure

Consider writing a validation class for password strength enforcement - when a user is required to choose a password that meets certain criteria for helping secure user accounts. Let us assume that the password security criteria enforce that the password:

The following class implements these validation criteria:

namespace MyValid;

use Zend\Validator\AbstractValidator;

class PasswordStrength extends AbstractValidator
{
    const LENGTH = 'length';
    const UPPER  = 'upper';
    const LOWER  = 'lower';
    const DIGIT  = 'digit';

    protected $messageTemplates = [
        self::LENGTH => "'%value%' must be at least 8 characters in length",
        self::UPPER  => "'%value%' must contain at least one uppercase letter",
        self::LOWER  => "'%value%' must contain at least one lowercase letter",
        self::DIGIT  => "'%value%' must contain at least one digit character",
    ];

    public function isValid($value)
    {
        $this->setValue($value);

        $isValid = true;

        if (strlen($value) < 8) {
            $this->error(self::LENGTH);
            $isValid = false;
        }

        if (! preg_match('/[A-Z]/', $value)) {
            $this->error(self::UPPER);
            $isValid = false;
        }

        if (! preg_match('/[a-z]/', $value)) {
            $this->error(self::LOWER);
            $isValid = false;
        }

        if (! preg_match('/\d/', $value)) {
            $this->error(self::DIGIT);
            $isValid = false;
        }

        return $isValid;
    }
}

Note that the four criteria tests in isValid() do not immediately return false. This allows the validation class to provide all of the reasons that the input password failed to meet the validation requirements. If, for example, a user were to input the string #$% as a password, isValid() would cause all four validation failure messages to be returned by a subsequent call to getMessages().