NAME
    Validation::Class - Self-Validating Object System and Data Validation
    Framework

VERSION
    version 7.85

SYNOPSIS
        package MyApp::User;

        use Validation::Class;

        mixin basic     => {
            required    => 1,
            max_length  => 255,
            filters     => [qw/trim strip/]
        };

        field login     => {
            mixin       => 'basic',
            min_length  => 5
        };

        field password  => {
            mixin       => 'basic',
            min_length  => 5,
            min_symbols => 1
        };

        package main;

        my $user = MyApp::User->new(login => 'admin', password => 'secr3t');

        unless ($user->validate('login', 'password')) {

            # do something with the errors,
            # e.g. print $user->errors_to_string

        }

        1;

    Validation::Class is a data validation framework and simple object
    system. It allows you to model data and construct objects with focus on
    structure, reusability and data validation. It expects user input errors
    (without dying), validation only occurs when you ask it to.
    Validation::Class classes are designed to ensure consistency and promote
    reuse of data validation rules.

    Validation::Class::Intro will help you better understand the framework's
    rationale and typical use-cases while Validation::Class::Prototype will
    help you discover all the bells-and-whistles included in the framework.

DESCRIPTION
    Validation::Class is much more than a robust data validation framework,
    in-fact it is more of a data modeling framework and can be used as an
    alternative to minimalistic object systems such as Moo, Mo, etc.
    Validation::Class aims to provide the building blocks for easily
    definable self-validating data models. For more information on the
    validation class object system, review "the object system" section.

    Validation classes are typically defined using the following keywords:

        * field     - a field is a data validation rule
        * mixin     - a field template
        * directive - a field/mixin rule attribute
        * filter    - a directive which transforms the field parameter value
        * method    - a self-validating sub-routine
        * object    - a simple object builder

    To keep your class namespace clean and free from pollution, all
    inherited functionality is configured on your class' prototype (a cached
    class configuration object) which leaves you free to create and
    overwrite method names in your class without breaking the
    Validation::Class framework, this all happens much in the same way Moose
    uses it's MOP (meta-object-protocol) having most of the framework
    functionality residing in the Moose::Meta namespace. For more
    information on the validation class prototype, review "the prototype
    class" section.

    One very important (and intentional) difference between Moose/Moose-like
    systems and Validation::Class classes is in the handling of errors.
    There are generally two types of errors that occur in an application,
    user-errors which are expected and should be handled and reported, and
    system-errors which are unexpected and should cause the application to
    terminate or otherwise handle the exception. It is not always desired
    and/or appropriate to crash from a failure to validate a particular
    parameter. In Validation::Class, the application is not terminated or
    validate automatically unless you configure it to.

    Additionally, please review the Validation::Class::Intro for a more
    in-depth understanding of how to leverage Validation::Class.

KEYWORDS
  attribute
    The attribute keyword (or has) creates a class attribute. This is only a
    minimalistic variant of what you may have encountered in other object
    systems such as Moose, Mouse, Moo, Mo, etc.

        package MyApp::User;

        use Validate::Class;

        attribute 'bothered' => 1;

        attribute 'attitude' => sub {

            return $self->bothered ? 1 : 0

        };

        1;

    The attribute keyword takes two arguments, the attribute name and a
    constant or coderef that will be used as its default value.

  build
    The build keyword (or bld) registers a coderef to be run at
    instantiation much in the same way the common BUILD routine is used in
    modern-day OO systems.

        package MyApp::User;

        use Validation::Class;

        build sub {

            my ($self, %args) = @_;

            # ... do something

        };

        # die like a Moose

        use Carp;

        build sub {

            my ($self, %args) = @_;

            my @attributes = qw();

            foreach my $attribute (@attributes) {

                confess "Attribute ($attribute) is required"
                    unless $self->$attribute;

            }

        };

    The build keyword takes one argument, a coderef which is passed the
    instantiated class object.

  directive
    The directive keyword (or dir) creates custom validator directives to be
    used in your field definitions. It is a means of extending the
    pre-existing directives table before runtime and is ideal for creating
    custom directive extension packages to be used in all your classes.

        package MyApp::Directives;

        use Validation::Class;
        use Data::Validate::Email;

        directive 'is_email' => sub {

            my ($dir, $value, $field, $self) = @_;

            my $validator = Data::Validate::Email->new;

            unless ($validator->is_email($value)) {

                my $handle = $field->{label} || $field->{name};

                $field->{errors}->add("$handle must be a valid email address");

                return 0;

            }

            return 1;

        };

        package MyApp::User;

        use Validate::Class;
        use MyApp::Directives;

        field 'email' => {
            is_email => 1,
            ...
        };

        1;

    The directive keyword takes two arguments, the name of the directive and
    a coderef which will be used to validate the associated field. The
    coderef is passed four ordered parameters, the value of directive, the
    value of the field (parameter value), the field object (hashref), and
    the instantiated class object. The validator MUST return true or false.

    Additionally, if you only desire to extend the list of acceptable
    directives, you can create a no-op by simply returning true, e.g.:

        directive 'new_addition' => sub {1};

  field
    The field keyword (or fld) creates a data validation rule for reuse and
    validation in code. The field name should correspond with the parameter
    name expected to be passed to your validation class.

        package MyApp::User;

        use Validation::Class;

        field 'login' => {
            required   => 1,
            min_length => 1,
            max_length => 255,
            ...
        };

    The field keyword takes two arguments, the field name and a hashref of
    key/values pairs known as directives.

    The field keyword also creates accessors which provide easy access to
    the field's corresponding parameter value(s). Accessors will be created
    using the field's name as a label having any special characters replaced
    with an underscore.

        field 'login' => {
            required   => 1,
            min_length => 1,
            max_length => 255,
            ...
        };

        field 'preference.send_reminders' => {
            required   => 1,
            max_length => 1,
            ...
        };

        my $value = $self->login;

        $self->login($new_value);

        $self->preference_send_reminders;

    Protip: Field directives are used to validate scalar and array data.
    Don't use fields to store and validate objects. Please see the *has*
    keyword instead or use an object system with type constraints like
    Moose.

  filter
    The filter keyword (or flt) creates custom filters to be used in your
    field definitions. It is a means of extending the pre-existing filters
    table before runtime and is ideal for creating custom directive
    extension packages to be used in all your classes.

        package MyApp::Directives;

        use Validation::Class;

        filter 'flatten' => sub {

            $_[0] =~ s/[\t\r\n]+/ /g;
            $_[0] # return

        };

        package MyApp::User;

        use Validate::Class;
        use MyApp::Directives;

        field 'description' => {
            filters => ['trim', 'flatten'],
            ...
        };

        1;

    The filter keyword takes two arguments, the name of the filter and a
    coderef which will be used to filter the value the associated field. The
    coderef is passed the value of the field and that value MUST be operated
    on directly. The coderef should also return the transformed value.

  method
    The method keyword (or mth) is used to create an auto-validating method.
    Similar to method signatures, an auto-validating method can leverage
    pre-existing validation rules and profiles to ensure a method has the
    required data necessary to proceed.

        package MyApp::User;

        use Validation::Class;

        method 'register' => {

            input  => ['name', '+email', 'login', '+password'],
            output => ['+id'], # optional output validation, dies on failure
            using  => sub {

                my ($self, @args) = @_;

                # .... do something registrationy

                $self->id(...); # set the ID field for output validation

                return $self;

            }

        };

        package main;

        my $user = MyApp::User->new(params => $params);

        if ($user->register) {
            ...
        }

        1;

    The method keyword takes two arguments, the name of the method to be
    created and a hashref of required key/value pairs. The hashref must have
    an "input" variable whose value is either an arrayref of fields to be
    validated, or a constant value which matches a validation profile name.
    The hashref must also have a "using" variable whose value is a coderef
    which will be executed upon successfully validating the input. Whether
    and what the method returns is yours to decide.

    Optionally the required hashref can have an "output" variable whose
    value is either an arrayref of fields to be validated, or a constant
    value which matches a validation profile name which will be used to
    perform data validation after the coderef has been executed. Please note
    that output validation failure will cause the program to die, the
    premise behind this decision is based on the assumption that given
    successfully validated input a routine's output should be predictable
    and if an error occurs it is most-likely a program error as opposed to a
    user error.

    See the ignore_failure and report_failure switch to control how method
    input validation failures are handled.

  mixin
    The mixin keyword (or mxn) creates a validation rules template that can
    be applied to any field using the mixin directive. Mixin directives are
    processed first so existing field directives will override the mixed-in
    directives.

        package MyApp::User;

        use Validation::Class;

        mixin 'constrain' => {
            required   => 1,
            min_length => 1,
            max_length => 255,
            ...
        };

        # e.g.
        field 'login' => {
            mixin => 'constrain',
            ...
        };

    The mixin keyword takes two arguments, the mixin name and a hashref of
    key/values pairs known as directives.

  profile
    The profile keyword (or pro) stores a validation profile (coderef) which
    as in the traditional use of the term is a sequence of validation
    routines that validate data relevant to a specific action.

        package MyApp::User;

        use Validation::Class;

        profile 'signup' => sub {

            my ($self, @args) = @_;

            # ... do other stuff

            return $self->validate(qw(
                +name
                +email
                +email_confirmation
                -login
                +password
                +password_confirmation
            ));

        };

        package main;

        my $user = MyApp::User->new(params => $params);

        unless ($user->validate_profile('signup')) {

            die $user->errors_to_string;

        }

    The profile keyword takes two arguments, a profile name and coderef
    which will be used to execute a sequence of actions for validation
    purposes.

METHODS
  new
    The new method instantiates a new class object, it performs a series of
    actions (magic) required for the class function properly, and for that
    reason, this method should never be overridden. Use the build keyword to
    hooking into the instantiation process.

        package MyApp;

        use Validation::Class;

        # optionally

        build sub {

            my ($self, @args) = @_; # is instantiated

        };

        package main;

        my $app = MyApp->new;

        ...

  prototype
    The prototype method (or proto) returns an instance of the associated
    class prototype. The class prototype is responsible for manipulating and
    validating the data model (the class). It is not likely that you'll need
    to access this method directly, see "THE PROTOTYPE CLASS" in
    Validation::Class.

        package MyApp;

        use Validation::Class;

        package main;

        my $app = MyApp->new;

        my $prototype = $app->prototype;

        ...

THE PROTOTYPE CLASS
    This module provides mechanisms (sugar functions to model your data)
    which allow you to define self-validating classes. Each class you create
    is associated with a *prototype* class which provides data validation
    functionality and keeps your class' namespace free from pollution,
    please see Validation::Class::Prototype for more information on specific
    methods, and attributes.

    All derived classes will have a prototype-class attached to it which
    does all the heavy lifting (regarding validation and error handling).
    The prototype injects a few proxy methods into your class which are
    basically aliases to your prototype class methods, however it is
    possible to access the prototype directly using the proto/prototype
    methods.

        package MyApp::User;

        use Validation::Class;

        package main;

        my $user  = MyApp::User->new;
        my $proto = $user->prototype;

        $proto->error_count # same as calling $self->error_count

THE OBJECT SYSTEM
    All derived classes will benefit from the light-weight, straight-forward
    and simple object system Validation::Class provides. The conventional
    constructor "new" should be used to instantiate a new object, and the
    "bld"/"build" keywords can be used to hook into the instantiation
    process. Your classes can be configured to cooperate with an existing
    design or modern OO framework like Moose, Mouse, Moo, etc. The following
    example explains how to setup a Validation::Class class in cooperation
    with Moose (while this example focuses on Moose, the approach is the
    same regardless of the existing system):

        # USING MOOSE AS YOUR PRIMARY OO SYSTEM

        package MyApp;

        use Moose;
        use Validation::Class '!has'; # in cooperative mode, dont export has()

        # you must run initialization routines yourself ...
        # specifying it in a BUILD routine will run it automatically

        sub BUILD {

            my ($self, $args) = @_;

            $self->initialize_validator(
                params => $args->{params}
            );

        }

        field login     => {
            min_length  => 5
            max_length  => 50
        };

        field password  => {
            min_length  => 8,
            min_symbols => 1
            max_length  => 50
        };

        # USING MOOSE AS YOUR SECONDARY/BACKUP OO SYSTEM

        package MyApp;

        use Validation::Class '!has'; # avoids has() keyword clash
        use Moose;

        field login     => {
            min_length  => 5
            max_length  => 50
        };

        field password  => {
            min_length  => 8,
            min_symbols => 1
            max_length  => 50
        };

        has database => (
            is  => 'rw',
            isa => 'DBI::db',
            ...
        );

        1;

    This cooperation works by simply detecting the existence of a method
    named "new", the name traditionally reserved for a class constructor
    which if detected signals Validation::Class to install a method named
    "initialize" as opposed to installing its own constructor. The installed
    method, "initialize", encapsulates the functionality which prepares the
    class for interaction with its corresponding prototype class, this
    function must be called before using the Validation::Class features
    provided. If this concept isn't clear to you you needn't worry as this
    is very low-level, all you need you understand is that Validation::Class
    will install a constructor or a method named initialize if a constructor
    already exists, either way, the installed method should be called before
    executing methods on the class.

    As previously stated, Validation::Class injects a few proxy methods into
    your class which are basically aliases to your prototype class methods.
    You can find additional information on the prototype class and its
    method at Validation::Class::Prototype. The following is a list of
    *proxy* methods, methods which are injected into your class as shorthand
    to methods defined in the prototype class (these methods are
    overridden):

  class
        $self->class;

    See "class" in Validation::Class::Prototype for full documentation.

  clear_queue
        $self->clear_queue;

    See "clear_queue" in Validation::Class::Prototype for full
    documentation.

  error_count
        $self->error_count;

    See "error_count" in Validation::Class::Prototype for full
    documentation.

  error_fields
        $self->error_fields;

    See "error_fields" in Validation::Class::Prototype for full
    documentation.

  errors
        $self->errors;

    See "errors" in Validation::Class::Prototype for full documentation.

    head2 errors_to_string

        $self->errors_to_string;

    See "errors_to_string" in Validation::Class::Prototype for full
    documentation.

  get_errors
        $self->get_errors;

    See "get_errors" in Validation::Class::Prototype for full documentation.

  get_fields
        $self->get_fields;

    See "get_fields" in Validation::Class::Prototype for full documentation.

  get_params
        $self->get_params;

    See "get_params" in Validation::Class::Prototype for full documentation.

  fields
        $self->fields;

    See "fields" in Validation::Class::Prototype for full documentation.

  filtering
        $self->filtering;

    See "filtering" in Validation::Class::Prototype for full documentation.

  ignore_failure
        $self->ignore_failure;

    See "ignore_failure" in Validation::Class::Prototype for full
    documentation.

  ignore_unknown
        $self->ignore_unknown;

    See "ignore_unknown" in Validation::Class::Prototype for full
    documentation.

  param
        $self->param;

    See "param" in Validation::Class::Prototype for full documentation.

  params
        $self->params;

    See "params" in Validation::Class::Prototype for full documentation.

  plugin
        $self->plugin;

    See "plugin" in Validation::Class::Prototype for full documentation.

  queue
        $self->queue;

    See "queue" in Validation::Class::Prototype for full documentation.

  report_failure
        $self->report_failure;

    See "report_failure" in Validation::Class::Prototype for full
    documentation.

  report_unknown
        $self->report_unknown;

    See "report_unknown" in Validation::Class::Prototype for full
    documentation.

  reset_errors
        $self->reset_errors;

    See "reset_errors" in Validation::Class::Prototype for full
    documentation.

  reset_fields
        $self->reset_fields;

    See "reset_fields" in Validation::Class::Prototype for full
    documentation.

  reset_params
        $self->reset_params;

    See "reset_params" in Validation::Class::Prototype for full
    documentation.

  set_errors
        $self->set_errors;

    See "set_errors" in Validation::Class::Prototype for full documentation.

  set_fields
        $self->set_fields;

    See "set_fields" in Validation::Class::Prototype for full documentation.

  set_params
        $self->set_params;

    See "set_params" in Validation::Class::Prototype for full documentation.

  set_method
        $self->set_method;

    See "set_method" in Validation::Class::Prototype for full documentation.

  stash
        $self->stash;

    See "stash" in Validation::Class::Prototype for full documentation.

  validate
        $self->validate;

    See "validate" in Validation::Class::Prototype for full documentation.

  validate_method
        $self->validate_method;

    See "validate_method" in Validation::Class::Prototype for full
    documentation.

  validate_profile
        $self->validate_profile;

    See "validate_profile" in Validation::Class::Prototype for full
    documentation.

EXTENDING VALIDATION::CLASS
    Validation::Class does NOT provide method modifiers but can be easily
    extended with Class::Method::Modifiers.

  before
     before foo => sub { ... };

    See "before method(s) => sub { ... }" in Class::Method::Modifiers for
    full documentation.

  around
     around foo => sub { ... };

    See "around method(s) => sub { ... }" in Class::Method::Modifiers for
    full documentation.

  after
     after foo => sub { ... };

    See "after method(s) => sub { ... }" in Class::Method::Modifiers for
    full documentation.

SEE ALSO
    Additionally you may want to look elsewhere for your data validation
    needs so the following is a list of recommended validation
    libraries/frameworks you might do well to look into. Validate::Tiny is
    nice for simple use-cases, it has virtually no dependencies and solid
    test coverage. Data::Verifier is a great approach towards adding robust
    validation options to your existing Moose classes. Also, I have also
    heard some good things about Data::FormValidator as well.

AUTHOR
    Al Newkirk <anewkirk@ana.io>

COPYRIGHT AND LICENSE
    This software is copyright (c) 2011 by Al Newkirk.

    This is free software; you can redistribute it and/or modify it under
    the same terms as the Perl 5 programming language system itself.

