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INTRODUCTION

Data validation is an important aspect of every application yet it is often overlooked or neglected. Data validation should be thought of as your data input firewall, a layer that exist between the user of your application and the application's business objects.

DATA VALIDATION PROBLEMS

To understand the problem domain we need to first ask ourselves:

    * what is data validation? and ... is that what I've been doing?
    * what are the common data validation requirements?
    * what are the common use-cases where validation becomes tricky?

Data validation is the process of auditing a piece of data to ensure it fits a specific criteria. Standard data validation requirements are:

    * existence checking
    * range checking
    * type checking
    * list-lookup checking
    * dependency checking
    * pattern checking
    * custom validation checking (business logic)

Typically when designing an application we tend to name input parameters in an arbitrarily fashion and validate the same data at various stages during a program's execution (duplicating logic and validation routines) in various places in the application stack. This approach is inefficient and prone to bugs, inconsistencies and security problems.

Data can be submitted to an application in various formats and it is not always ideal, and the option to pre-format the data is not always ideal or even possible. A few common use-cases were validation is required and often fails (in a big big way) are as follows:

    * handling arbitrarily and/or dynamically-named parameters
    * handling input for batch-processing
    * handling multi-type parameters (array or scalar depending on context)
    * handling complex conditional validation logic
    * handling multi-variant parameter names (aliases)
    * handling parameter dependencies
    * handling errors (reporting messages, localization, etc)

A DATA VALIDATION SOLUTION

A proper validation framework should allow you to model data and construct validation objects with a focus on structuring rules, reusing common declarations, defining input filters and validating data. Its main purpose should be to properly handle data input errors. It's ulterior motive should be to ensure consistency and promote reuse of data validation rules.

WHY VALIDATION::CLASS

Validation classes derived from Validation::Class are typically configured using the Validation::Class sugar functions (or keywords). Validation classes are typically defined using the following keywords:

    * field     - a data validation rule that matches an input parameter
    * mixin     - a configuration template which can be merged with a field
    * directive - a field/mixin rule corresponding to a directive class name
    * filter    - a custom filtering routine which transforms a field value
    * method    - a self-validating sub-routine w/ associated validation profile

A data validation framework exists to handle failures, it is its main function and purpose, in-fact, the difference between a validation framework and a type-constraint system is how it responds to errors.

There are generally two types of errors that occur in an application, user-errors which are expected and should be handled and reported so that a user can correct the problem, and system-errors which are unexpected and should cause the application to terminate and/or handling the exception. Exception handling is the process of responding to the occurrence, during computation, of exceptions (anomalous or exceptional situations).

User errors and system errors are poplar opposites. It is not always desired and/or appropriate to crash from a failure to validate user input. The following examples should clearly display how Validation::Class addresses key pain-points and handles common use-cases were validation is usually quite arduous.

    # handling arbitrary and/or dynamically-named parameters

    package DynamicParameters;

    use Validation::Class;

    field email     => {
        required    => 1,
        pattern     => qr/\@localhost$/
    };

    field login     => {
        required    => 1,
        min_length  => 5,
        alias       => ['user']
    };

    field password  => {
        required    => 1,
        min_length  => 5,
        min_digits  => 1,
        alias       => ['pass']
    };

    package main;

    my $params = {
        user    => 'admin',             # arbitrary
        pass    => 's3cret',            # arbitrary
        email_1 => 'admin@localhost',   # dynamic created
        email_2 => 'root@localhost',    # dynamic created
        email_3 => 'sa@localhost',      # dynamic created
    };

    my $dp = DynamicParameters->new(params => $params);

    $dp->proto->clone_field('email', $_)
        for $dp->params->grep(qr/^email/)->keys
    ;

    print $dp->validate ? "OK" : "NOT OK";

    1;

    # handling input for batch-processing

    package BatchProcessing;

    use Validation::Class;

    mixin scrub     => {
        required    => 1,
        filters     => ['trim', 'strip']
    };

    field header    => {
        mixin       => 'scrub',
        options     => ['name', 'email', 'contact', 'dob', 'country'],
        multiples   => 1 # handle param as a scalar or arrayref
    };

    field name      => {
        mixin       => 'scrub',
        filters     => ['titlecase'],
        min_length  => 2
    };

    field email     => {
        mixin       => 'scrub',
        min_length  => 3
    };

    field contact   => {
        mixin       => 'scrub',
        length      => 10
    };

    field dob       => {
        mixin       => 'scrub',
        length      => 8,
        pattern     => '##/##/##'
    };

    field country   => {
        mixin       => 'scrub'
    };

    package main;

    my $params = {
        pasted_data => q{
            name        email   contact dob     country
            john        john@zuzu.com   9849688899      12/05/98        UK
            jim kathy   kjim@zuz.com    8788888888      05/07/99        India
            Federar     fed@zuzu.com    4484848989      11/21/80        USA
            Micheal     micheal@zuzu.com        6665551212      06/10/87        USA
            Kwang Kit   kwang@zuzu.com  7775551212      07/09/91        India
            Martin      jmartin@zuzu.com        2159995959      02/06/85        India
            Roheeth     roheeth@zuzu.com        9596012020      01/10/89        USA
        }
    };

    # ... there are many ways this could be parsed and validated
    # ... but this is simple

    my $bpi = my @pasted_lines = map { s/^\s+//; $_ } split /\n/, $params->{pasted_data};
    my @headers = split /\t/, shift @pasted_lines;

    my $bp  = BatchProcessing->new(params => { header => [@headers] });

    # validate headers first

    if ($bp->validate) {

        $bp->params->clear;

        $bpi--;

        # validate each line, halt on first bad line

        while (my $line = shift @pasted_lines) {

            my @data = split /\t/, $line;

            for (my $i=0; $i<@data; $i++) {

                $bp->params->add($headers[$i], $data[$i]);

            }

            last unless $bp->validate;

            $bp->params->clear;

            $bpi--;

        }

    }

    print ! $bpi ? "OK" : "NOT OK";

    1;

    # handling multi-type parameters (array or scalar depending on context)

    package MultiType;

    use Validation::Class;

    field letter_type => {

        required  => 1,
        options   => [ 'A' .. 'Z' ],
        multiples => 1 # turn on multi-type processing

    };

    package main;

    my $mt = MultiType->new;
    my $ok = 0;

    $mt->params->add(letter_type => 'A');

    $ok++ if $mt->validate;

    $mt->params->clear->add(letter_type => ['A', 'B', 'C']);

    $ok++ if $mt->validate;

    print $ok == 2 ? "OK" : "NOT OK";

    1;

    # handling complex conditional validation logic

    package ComplexCondition;

    use Validation::Class;

    mixin scrub      => {
        required     => 1,
        filters      => ['trim', 'strip']
    };

    mixin flag       => {
        length       => 1,
        options      => [0, 1]
    };

    field first_name => {
        mixin        => 'scrub',
        filters      => ['titlecase']
    };

    field last_name  => {
        mixin        => 'scrub',
        filters      => ['titlecase']
    };

    field role       => {
        mixin        => 'scrub',
        filters      => ['titlecase'],
        options      => ['Client', 'Employee', 'Administrator'],
        default      => 'Client'
    };

    field address    => {
        mixin        => 'scrub',
        required     => 0,
        depends_on   => ['city', 'state', 'zip']
    };

    field city       => {
        mixin        => 'scrub',
        required     => 0,
        depends_on   => 'address'
    };

    field state      => {
        mixin        => 'scrub',
        required     => 0,
        length       => '2',
        pattern      => 'XX',
        depends_on   => 'address'
    };

    field zip        => {
        mixin        => 'scrub',
        required     => 0,
        length       => '5',
        pattern      => '#####',
        depends_on   => 'address'
    };

    field has_mail   => {
        mixin        => 'flag'
    };

    profile 'registration' => sub {

        my ($self) = @_;

        # address info not required unless role is client or has_mail is true

        return unless $self->validate('has_mail');

        $self->queue(qw/first_name last_name/);

        if ($self->param('has_mail') || $self->param('role') eq 'Client') {

            # depends_on directive kinda makes city, state and zip required too
            $self->queue(qw/+address/);

        }

        my $ok = $self->validate;

        $self->clear_queue;

        return $ok;

    };

    package main;

    my $ok = 0;
    my $mt;

    $mt = ComplexCondition->new(
        first_name => 'Rachel',
        last_name  => 'Green'
    );

    # defaults to client, missing address info
    $ok++ if ! $mt->validate_profile('registration');

    $mt = ComplexCondition->new(
        first_name => 'monica',
        last_name  => 'geller',
        role       => 'employee'
    );

    # filters (pre-process) role and titlecase, as employee no address needed
    $ok++ if $mt->validate_profile('registration');

    $mt = ComplexCondition->new(
        first_name => 'phoebe',
        last_name  => 'buffay',
        address    => '123 street road',
        city       => 'nomans land',
        state      => 'zz',
        zip        => '54321'
    );

    $ok++ if $mt->validate_profile('registration');

    print $ok == 3 ? "OK" : "NOT OK";

    1;

    # handling multi-variant parameter names (aliases)

    package MultiName;

    use Validation::Class;

    field login => {

        required    => 1,
        min_length  => 5, # must be 5 or more chars
        min_alpha   => 1, # must have at-least 1 alpha char
        min_digits  => 1, # must have at-least 1 digit char
        min_symbols => 1, # must have at-least 1 non-alphanumeric char
        alias       => [
            'signin',
            'username',
            'email',
            'email_address'
        ]

    };

    package main;

    my $ok = 0;

    # fail
    $ok++ if ! MultiName->new(login => 'miso')->validate;

    # nice
    $ok++ if MultiName->new(login => 'm!s0_soup')->validate;

    # no signin field exists, however, the alias directive pre-processing DWIM
    $ok++ if MultiName->new(signin => 'm!s0_soup')->validate;

    # process aliases
    $ok++ if MultiName->new(params => {signin        => 'm!s0_soup'})->validate;
    $ok++ if MultiName->new(params => {username      => 'm!s0_soup'})->validate;
    $ok++ if MultiName->new(params => {email         => 'm!s0_soup'})->validate;
    $ok++ if MultiName->new(params => {email_address => 'm!s0_soup'})->validate;

    print $ok == 7 ? "OK" : "NOT OK";

    1;

    # handling parameter dependencies

    package ParamDependencies;

    use Validation::Class;

    mixin scrub      => {
        required     => 1,
        filters      => ['trim', 'strip']
    };

    mixin flag       => {
        length       => 1,
        options      => [0, 1]
    };

    field billing_address => {
        mixin        => 'scrub',
        required     => 1,
        depends_on   => ['billing_city', 'billing_state', 'billing_zip']
    };

    field billing_city => {
        mixin        => 'scrub',
        required     => 0,
        depends_on   => 'billing_address'
    };

    field billing_state => {
        mixin        => 'scrub',
        required     => 0,
        length       => '2',
        pattern      => 'XX',
        depends_on   => 'billing_address'
    };

    field billing_zip => {
        mixin        => 'scrub',
        required     => 0,
        length       => '5',
        pattern      => '#####',
        depends_on   => 'billing_address'
    };

    field shipping_address => {
        mixin_field  => 'billing_address',
        depends_on   => ['shipping_city', 'shipping_state', 'shipping_zip']
    };

    field shipping_city => {
        mixin_field  => 'billing_city',
        depends_on   => 'shipping_address'
    };

    field shipping_state => {
        mixin_field  => 'billing_state',
        depends_on   => 'shipping_address'
    };

    field shipping_zip => {
        mixin_field  => 'billing_zip',
        depends_on   => 'shipping_address'
    };

    field same_billing_shipping => {
        mixin        => 'flag'
    };

    profile 'addresses' => sub {

        my ($self) = @_;

        return unless $self->validate('same_billing_shipping');

        # billing and shipping address always required
        $self->validate(qw/+billing_address +shipping_address/);

        # address must match if option is selected
        if ($self->param('same_billing_shipping')) {

            foreach my $param ($self->params->grep(qr/^shipping_/)->keys) {

                my ($suffix) = $param =~ /^shipping_(.*)/;

                my $billing  = $self->param("billing_$suffix");
                my $shipping = $self->param("shipping_$suffix");

                # shipping_* must match billing_*
                unless ($billing eq $shipping) {
                    $self->errors->add(
                        "Billing and shipping addresses do not match"
                    );
                    last;
                }

            }

        }

        return $self->error_count ? 0 : 1;

    };

    package main;

    my $ok = 0;
    my $pd;

    $pd = ParamDependencies->new(
        billing_address => '10 liberty boulevard',
        billing_city    => 'malvern',
        billing_state   => 'pa',
        billing_zip     => '19355'
    );

    # missing shipping address info
    $ok++ if ! $pd->validate_profile('addresses');

    $pd = ParamDependencies->new(
        billing_address  => '10 liberty boulevard',
        billing_city     => 'malvern',
        billing_state    => 'pa',
        billing_zip      => '19355',

        shipping_address => '301 cherry street',
        shipping_city    => 'pottstown',
        shipping_state   => 'pa',
        shipping_zip     => '19464'
    );

    $ok++ if $pd->validate_profile('addresses');

    $pd = ParamDependencies->new(
        billing_address  => '10 liberty boulevard',
        billing_city     => 'malvern',
        billing_state    => 'pa',
        billing_zip      => '19355',

        same_billing_shipping => 1,

        shipping_address => '301 cherry street',
        shipping_city    => 'pottstown',
        shipping_state   => 'pa',
        shipping_zip     => '19464'
    );

    # billing and shipping don't match
    $ok++ if ! $pd->validate_profile('addresses');

    $pd = ParamDependencies->new(
        billing_address  => '10 liberty boulevard',
        billing_city     => 'malvern',
        billing_state    => 'pa',
        billing_zip      => '19355',

        same_billing_shipping => 1,

        shipping_address => '10 liberty boulevard',
        shipping_city    => 'malvern',
        shipping_state   => 'pa',
        shipping_zip     => '19355'
    );

    $ok++ if $pd->validate_profile('addresses');

    print $ok == 4 ? "OK" : "NOT OK";

    1;

GETTING STARTED

ADDITIONAL INSIGHT

AUTHOR

COPYRIGHT AND LICENSE

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