The following example demonstrates how a very simple custom validator might be written. In this case the validation rules are simply that the input value must be a floating point value.

class MyValid_Float extends Zend_Validate_Abstract
{
    const FLOAT = 'float';

    protected $_messageTemplates = array(
        self::FLOAT => "'%value%' is not a floating point value"
    );

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

        if (!is_float($value)) {
            $this->_error();
            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.

The following example demonstrates a more complex set of validation rules, where it is required that the input value be numeric and within the range of minimum and maximum boundary values. 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:

class MyValid_NumericBetween extends Zend_Validate_Abstract
{
    const MSG_NUMERIC = 'msgNumeric';
    const MSG_MINIMUM = 'msgMinimum';
    const MSG_MAXIMUM = 'msgMaximum';

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

    protected $_messageVariables = array(
        'min' => 'minimum',
        'max' => 'maximum'
    );

    protected $_messageTemplates = array(
        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.

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:

class MyValid_PasswordStrength extends Zend_Validate_Abstract
{
    const LENGTH = 'length';
    const UPPER  = 'upper';
    const LOWER  = 'lower';
    const DIGIT  = 'digit';

    protected $_messageTemplates = array(
        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().