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devdata/http_advent.perldancer.org_2018_22  view on Meta::CPAN 

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<title> Parameter testing with Dancer2::Plugin::ParamTypes | PerlDancer Advent Calendar</title>
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<a href="/" class="homelink">Dancer Advent Calendar</a><br />

<p>
The PerlDancer Advent Calendar is a community-driven project that aims 
to showcase the Dancer Perl web framework.
</p>

<p>
Each day of December until Christmas, one article about Dancer. Stay tuned for new moves!
</p>

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    <h3>About Dancer</h3>
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        <li><a href="http://www.perldancer.org/">Dancer homepage</a></li>
        <li><a href="http://twitter.com/PerlDancer">Official Twitter</a></li>
        <li><a href="http://github.com/PerlDancer/Dancer">Dancer on GitHub</a></li>
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<div class="pod-document"><h1><a name="parameter_testing_with_dancer2__plugin__paramtypes"></a>Parameter testing with Dancer2::Plugin::ParamTypes</h1>

<p>The most common web code you will ever write is testing your parameters.
You might as well have a good way to do this.</p>
<h2><a name="in_the_old_ages"></a>In the old ages</h2>

<p>Way back then, we used to write code to check all of our arguments.</p>
<p>If we had a route that includes some ID, we would check that we
received it and that it matches the type we want. We would then decide
what to do if it doesn't match. Over time, we would clean up and
refactor, and try to reuse the checking code.</p>
<p>For example:</p>
<pre class="prettyprint">use Dancer2;
get '/:id' =&gt; sub {
    my $id = route_parameters-&gt;{'id'};
    if ( $id !~ /^[0-9]+$/ ) {
        send_error 'Bad ID' =&gt; 400;
    }

    # optional
    my $action = query_parameters-&gt;{'action'};
    unless ( defined $action &amp;&amp; length $action ) {
        send_error 'Bad Action' =&gt; 400;
    }

    # use $id and maybe $action
};</pre>

<p>The more parameters we have, the more annoying it is to write these
tests.</p>
<p>But what's more revealing here is that this validation code is not
actually part of our web code. It's input validation <i>for</i> our web
code.</p>
<h2><a name="a_different_perspective"></a>A different perspective</h2>

<p>What if - instead of having to write all of this code - we maintained
the Dancer2 spirit and allowed you to <b>declare</b> what your validation
rules are, and have Dancer2 do the work for you?</p>

devdata/http_advent.perldancer.org_2018_22  view on Meta::CPAN 

but you can decide to act differently by registering a different
action.</p>
<pre class="prettyprint">register_type_action 'SoftError' =&gt; sub {
    my ( $self, $details ) = @_;

    warning "Parameter $details-&gt;{'name'} from $details-&gt;{'source'} "
          . "failed checking for type $details-&gt;{'type'}, called "
          . "action $details-&gt;{'action'}";

    return;
};

get '/:id' =&gt; with_types [
    [ 'query', 'age', 'Int', 'SoftError',
] =&gt; sub {...};</pre>

<p>On a bad <code>age</code> parameter, it will print out the following warning:</p>
<pre class="prettyprint">Parameter age from query failed checking for type Int, called action SoftError</pre>

<p>This means you can also register a set of actions that you want to call
in different cases.</p>
<h2><a name="conclusion"></a>Conclusion</h2>

<p><a href="https://metacpan.org/module/Dancer2::Plugin::ParamTypes">Dancer2::Plugin::ParamTypes</a> allows you to define your own types and
your own actions, to create your own plugin that helps you maintain
reusability and consistency across your application with fewer code
duplication and less effort.</p>
<h2><a name="author"></a>Author</h2>

<p>This article has been written by Sawyer X for the Perl
Dancer Advent Calendar 2018.</p>
<h2><a name="copyright"></a>Copyright</h2>

<p>No copyright retained. Enjoy.</p>
<p>2018 // Sawyer X <code>&lt;xsawyerx@cpan.org&gt;</code></p>
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