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

VERSION
    version 7.04

SYNOPSIS
        package MyVal::User;
    
        use Validation::Class;
    
        # rules mixin
    
        mxn basic       => {
            required    => 1,
            max_length  => 255,
            filters     => [qw/trim strip/]
        }; 
    
        # attr(s) w/rules
    
        fld id          => {
            mixin       => 'basic',
            max_length  => 11,
            required    => 0
        };
    
        fld name        => {
            mixin       => 'basic',
            min_length  => 2
        };
    
        fld email       => {
            mixin       => 'basic',
            min_length  => 3
        };
    
        fld login       => {
            mixin       => 'basic',
            min_length  => 5
        };
    
        fld password    => {
            mixin       => 'basic',
            min_length  => 5,
            min_symbols => 1
        };
    
        # just an attr
    
        has attitude => 1; 
    
        # self-validating method (even better than method signatures)
    
        mth create  => {
    
            input   => [qw/name email login password/],
            output  => ['+id'],
        
            using   => sub {
            
                my ($self, @args) = @_;
            
                # make sure to set id for output validation
            
            }
    
        }; 
    
        package main;
    
        my $user = MyVal::User->new(name => '...', email => '...');
    
        unless ($user->create) {
    
            # did you forget your login and pass?
    
        }
    
        1;

    Validation::Class takes a different approach towards data modeling and
    validation, it centralizes data validation rules to ensure consistency
    through DRY (dont-repeat-yourself) code.

        use MyApp;
    
        my $params = {
           'user.login' => '...',
           'user.pass' => '...'
        };
    
        my $app = MyApp->new(params => $params);
    
        my $user = $app->class('user'); # instantiated MyApp::User object
    
        unless ($user->validate('login', 'pass')){
    
            # do something with ... $input->errors;
    
        }

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.

    When fields (attributes with validation rules) are defined, accessors
    are automatically generated to make getting and setting their values
    much easier.

    Methods can be defined using the method keyword to create a
    self-validating method, checking the defined input requirements against
    existing validation rules before executing the routine, gaining
    consistency and security.

KEYWORDS
  attribute
    The attribute keyword (or has) creates a class attribute.

        package MyApp::User;
    
        use Validate::Class;
    
        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 = shift;
        
            # ... do something
        
        };

    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};
            
                $self->errors->add_error("$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 an attribute with validation rules
    for reuse 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,
            ...
        };
    
        field 'preference.send_reminders.text:0' => {
            ...
        };
    
        my $value = $self->login;
    
        $self->login($new_value); # arrayrefs and hashrefs will be flattened
    
        $self->preference_send_reminders($value);
    
        $self->preference_send_reminders_text_0($value);

    Protip: Field directives are used to validate scalar and array data.
    Don't use fields to store and validate blessed objects. Please see the
    *has* keyword instead.

  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.

  load
    The load keyword (or set), which can also be used as a method, provides
    options for extending the current class by attaching other
    Validation::Class classes as relatives, roles, plugins, etc. The process
    of applying roles to the current class mainly involve copying the role's
    methods and configuration.

        package MyApp;
    
        use Validation::Class;
    
        # load stuff (extend MyApp)
    
        load {
            ...
        };
    
        1;

    The "load.classes" option, can be a constant or arrayref and uses
    Module::Find to load all child classes (in-all-subdirectories) for
    convenient access through the class() method. Existing parameters and
    configuration options are passed to the child class' constructor. All
    attributes can be easily overwritten using the attribute's accessors on
    the child class. These child classes are often referred to as relatives.
    This option accepts a constant or an arrayref of constants.

        package MyApp;
    
        use Validation::Class;
    
        # load all child classes
    
        load {
            classes => [
                __PACKAGE__
            ]
        };
    
        package main;
    
        my $app = MyApp->new;
    
        my $rel = $app->class('relative'); # new MyApp::Relative object
    
        my $rel = $app->class('data_source'); # MyApp::DataSource
        my $rel = $app->class('datasource-first'); # MyApp::Datasource::First
    
        1;

    The "load.plugins" option is used to load plugins that support
    Validation::Class. A Validation::Class plugin is little more than a
    class that implements a "new" method that extends the associated
    validation class object. As usual, an official Validation::Class plugin
    can be referred to using shorthand while custom plugins are called by
    prefixing a plus symbol to the fully-qualified plugin name. Learn more
    about plugins at Validation::Class::Intro. This option accepts a
    constant or an arrayref of constants.

        package MyVal;
    
        load {
            plugins => [
                'CPANPlugin', # Validation::Class::Plugin::CPANPlugin
                '+MyVal::Plugin'
            ]
        };
    
        1;

    The "load.roles" option is used to load and inherit functionality from
    child classes, these classes should be used and thought-of as roles. Any
    validation class can be used as a role with this option. This option
    accepts a constant or an arrayref of constants.

        package MyVal::User;
    
        load {
            roles => [
                'MyVal::Person'
            ]
        };
    
        1;

  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) = @_;
        
            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) = @_; # 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 (current class). It is not likely that you'll
    need to access this method directly.

        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 your
    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, 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 standard *new*
    method should be used to instantiate a new object and the *bld/build*
    keywords can be used to hook into the instantiation process.
    Validation::Class does NOT provide method modifiers but can be 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.

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.

