<?xml version="1.0" encoding="UTF-8"?>
<!-- Reviewed: no -->
<sect1 id="zend.validate.writing_validators">

    <title>Writing Validators</title>

    <para>
        Zend_Validate supplies a set of commonly needed validators, but inevitably, developers will
        wish to write custom validators for their particular needs. The task of writing a custom
        validator is described in this section.
    </para>

    <para>
        <classname>Zend_Validate_Interface</classname> defines three methods,
        <code>isValid()</code>, <code>getMessages()</code>, and <code>getErrors()</code>, that may
        be implemented by user classes in order to create custom validation objects. An object that
        implements <classname>Zend_Validate_Interface</classname> interface may be added to a
        validator chain with <classname>Zend_Validate::addValidator()</classname>. Such objects may
        also be used with <link
            linkend="zend.filter.input"><classname>Zend_Filter_Input</classname></link>.
    </para>

    <para>
        As you may already have inferred from the above description of
        <classname>Zend_Validate_Interface</classname>, validation classes provided with Zend
        Framework return a boolean value for whether or not a value validates successfully. They
        also provide information about <emphasis>why</emphasis> a value failed validation. The
        availability of the reasons for validation failures may be valuable to an application for
        various purposes, such as providing statistics for usability analysis.
    </para>

    <para>
        Basic validation failure message functionality is implemented in
        <classname>Zend_Validate_Abstract</classname>. To include this functionality when creating a
        validation class, simply extend <classname>Zend_Validate_Abstract</classname>. In the
        extending class you would implement the <code>isValid()</code> 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 <code>isValid()</code> should
        return <constant>FALSE</constant>. If the value passes your validation tests, then
        <code>isValid()</code> should return <constant>TRUE</constant>.
    </para>

    <para>
        In general, the <code>isValid()</code> 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.
    </para>

    <example id="zend.validate.writing_validators.example.simple">

        <title>Creating a Simple Validation Class</title>

        <para>
            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.

            <programlisting language="php"><![CDATA[
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;
    }
}
]]></programlisting>

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

    </example>

    <example id="zend.validate.writing_validators.example.conditions.dependent">

        <title>Writing a Validation Class having Dependent Conditions</title>

        <para>
            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:

            <itemizedlist>
                <listitem>
                    <para>The input value is not numeric.</para>
                </listitem>
                <listitem>
                    <para>The input value is less than the minimum allowed value.</para>
                </listitem>
                <listitem>
                    <para>The input value is more than the maximum allowed value.</para>
                </listitem>
            </itemizedlist>
        </para>

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

            <programlisting language="php"><![CDATA[
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;
    }
}
]]></programlisting>

            The public properties <code>$minimum</code> and <code>$maximum</code> 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 <code>min</code> and <code>max</code> to be used in
            message templates as magic parameters, just as with <code>value</code>.
        </para>

        <para>
            Note that if any one of the validation checks in <code>isValid()</code> fails, an
            appropriate failure message is prepared, and the method immediately returns
            <constant>FALSE</constant>. 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.
        </para>

    </example>

    <example id="zend.validate.writing_validators.example.conditions.independent">

        <title>Validation with Independent Conditions, Multiple Reasons for Failure</title>

        <para>
            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:

            <itemizedlist>
                <listitem>
                    <para>is at least 8 characters in length,</para>
                </listitem>
                <listitem>
                    <para>contains at least one uppercase letter,</para>
                </listitem>
                <listitem>
                    <para>contains at least one lowercase letter,</para>
                </listitem>
                <listitem>
                    <para>and contains at least one digit character.</para>
                </listitem>
            </itemizedlist>
        </para>

        <para>
            The following class implements these validation criteria:

            <programlisting language="php"><![CDATA[
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;
    }
}
]]></programlisting>

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

    </example>

</sect1>
<!--
vim:se ts=4 sw=4 et:
-->
