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<title> Customizing and extending your Dancer2 application generation | PerlDancer Advent Calendar</title>
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<a href="/" class="homelink">Dancer Advent Calendar</a><br />

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The PerlDancer Advent Calendar is a community-driven project that aims 
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Each day of December until Christmas, one article about Dancer. Stay tuned for new moves!
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<div class="pod-document"><h1><a name="customizing_and_extending_your_dancer2_application_generation"></a>Customizing and extending your Dancer2 application generation</h1>

<p>Dancer2 provides a useful command line that helps you generate a
Dancer2 application skeleton without having to write it yourself.</p>
<p>For example, creating an app called <code>My::Web::App</code>, you can run the following:</p>
<pre class="prettyprint">dancer2 gen -a My::Web::App</pre>

<p>The <code>dancer2</code> command line has a few more options, which you can see, if
you run <code>dancer2 gen --help</code>.</p>
<h2><a name="changing_the_skeleton"></a>Changing the skeleton</h2>

<p>Dancer2 generates a skeleton that it useful for most developers, but if
you are a seasoned Dancer2 developer, you might have a set of
preferences not represented in the default skeleton.</p>
<p>If it's different file setup that you want to have, you could partially
achieve it with the <code>dancer2 gen -s DIRECTORY</code>, indicating a different
skeleton directory. But that doesn't fix all of it.</p>
<p>To have full control over the entire scaffolding operation, you will
need to have control of the command line implementation. Let me show
you how.</p>
<h2><a name="extending_in_a_class"></a>Extending in a class</h2>

<p>To extend the application in a class, you will need to write a new
class with a new command. That class will then need to be loaded in your
environment for you to enjoy it.</p>
<p>There are two options:</p>
<ul>
<li>
<p>Write a new distribution with your new module and install it locally. Done.</p>
</li>
<li>
<p>Write a new module and make the directory in which it sits available in
your <code>$PERL5LIB</code> environment variable.</p>
<p>This option is more useful for companies that have a big library
directory that is always available in the include directories list.</p>
<p>An example of this:</p>
<pre class="prettyprint"># Creating the directory
$ mkdir -p /opt/perl/lib/Dancer2/CLI/Command/
$ cd /opt/perl/lib/Dancer2/CLI/Command/

# Putting a mostly-empty file
$ echo -e "package Dancer2::CLI::Command::new;\n1;" &gt;&gt; new.pm

# Now making sure this path is in PERL5LIB
# (replace the bashrc file path with your system's path)
echo "export PERL5LIB="/opt/perl/lib/:$PERL5LIB" &gt;&gt; /etc/bash.bashrc</pre>

</li>
</ul>
<h2><a name="writing_your_own_command"></a>Writing your own command</h2>

<p><a href="https://metacpan.org/module/Dancer2">Dancer2</a> uses <a href="https://metacpan.org/module/App::Cmd">App::Cmd</a> to implement the <code>dancer2</code> command line
utility. This means you can introduce additional commands by just implementing
a class.</p>
<h3><a name="writing_a_new_command"></a>Writing a new command</h3>

<pre class="prettyprint">package Dancer2::CLI::Command::activate
use strict;
use warnings;
use Path::Tiny qw&lt; path &gt;;
use App::Cmd::Setup -command;

sub description { 'Activating our application' }

sub opt_desc {
    return (
        [ 'directory|d', 'Application directory' ],
        # More options...
    );
}

sub validate_args {
    my ( $self, $opt, $args ) = @_;
    $opts-&gt;{'directory'}
        or $self-&gt;usage_error('You did not provide a directory');

    path( $opt-&gt;{'directory'} )-&gt;is_dir
        or $self-&gt;usage_error('Path provided is not a directory');
}

sub execute {
    my ( $self, $opt, $args ) = @_;
    my $dir = $opts-&gt;{'directory'};
    # Implement the application activation
    # (Whatever that means...)
}

1;</pre>

<p>In this example, we introduce a new command to <code>dancer2</code>. As long as
this class is available in your path (such as via your <code>$PERL5LIB</code>
environment variable), you will be able to run the following:</p>
<pre class="prettyprint">$ dancer2 activate --directory foo/</pre>

<p>(The implementation of what "activation" means in this context is left
to the reader.)</p>
<p>But what if you want to provide an alteration of an existing command -
the generation of the Dancer2 application?</p>
<h3><a name="writing_a_new_command"></a>Writing a new command</h3>

<p>Let's say you have a set of adjustments you keep doing to your
[company's] Dancer2 applications and you want to make these a default.</p>
<p>You can write it as a new command or you can subclass the existing
command and do whatever alterations you want before, during, and after
the generation of the skeleton.</p>
<pre class="prettyprint">package Dancer2::CLI::Command::mygen;
use strict;
use warnings;
use Cwd (); # Our own dependencies

# Subclass the existing "gen" command
use parent 'Dancer2::CLI::Command::gen';

sub execute {
  my ( $self, $opt, $args ) = @_;

  # Do whatever you want in this area, before we generate

  # For example, let's make sure the application
  # matches a certain naming convention

  my $app_name = $opt-&gt;{'application'};
  $app_name =~ /^My::Company::App::/
    or $self-&gt;usage_error('App must be prefixed by "My::Company::App");

  # Maybe check we are only scaffolding in a particular directory
  cwd() eq '/opt/my_company/webapps/'
      or $self-&gt;usage_error('Only create apps in our webapps directory');

  # At this point, we can run the original scaffolding
  $self-&gt;SUPER::execute( $opt, $args );

  # Now we finished generating, but we can contineu customizing what we have
}

1;</pre>

<p>Writing your own generation on top of the existing generation allows
you to manage the input (including additional validation) and the
output, giving you full control over the scaffolding process.</p>
<p>Some examples on which customizations you might want to perform:</p>
<ul>
<li><a name="item_Add_additional_default_imported_classes"></a><b>Add additional default imported classes</b>
</li>
<li><a name="item_Change_the_output_directory_name"></a><b>Change the output directory name</b>
</li>
<li><a name="item_Update_a_database_that_we_have_a_new_application"></a><b>Update a database that we have a new application</b>
</li>
<li><a name="item_Update_your_team_with_an_email_or_IRC_Slack_message"></a><b>Update your team with an email or IRC/Slack message</b>
</li>
<li><a name="item_Remove_files_that_are_not_applicable_for_your_setup_and_add_new_ones"></a><b>Remove files that are not applicable for your setup and add new ones</b>
</li>
<li><a name="item_Write_helpful_output_for_the_developer_who_scaffolded_the_app"></a><b>Write helpful output for the developer who scaffolded the app</b>
</li>
</ul>
<h2><a name="conclusion"></a>Conclusion</h2>

<p>I hope you find these techniques useful to introduce customization for
your home-grown Dancer2 application setup. I know I do. :)</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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