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Terrence Brannon > HTML-Seamstress-6.112830 > HTML::Seamstress::Quickstart


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HTML::Seamstress::Quickstart - A gentle introduction to HTML::Seamstress

Introduction ^

This guide is designed to get you started with dynamically generating and modifying ("templating") HTML with HTML::Seamstress.

We will work through several examples, with each one increasing your ability to work with Seamstress effectively.

Sample files

All the files for the samples are in the directory lib/HTML/Seamstress/Quickstart

Pure TreeBuilder ^

Welcome to the first example. This is our bare-bones example. Let's say we want to dynamically modify the following HTML:

<tt>pod_code 'Quickstart/html/greeting.html'</tt>

Let's not use Seamstress at all in this case. Remember Seamstress just makes using HTML::Tree more convenient when writing software - it is completely optional and totally non-magical. So here's the (admittedly verbose) pure TreeBuilder solution:

<tt>pod_code 'Quickstart/'</tt>

There's a convenience function in HTML::Element::Library which makes it easy to replace all the content of an element. This will make our script shorter. If we simply use Seamstress, its new_from_file() method will bless the HTML tree into a class which inherits from HTML::Element::Library, making it easy for us to shorten our program. So let's rework the example using bare-bones Seamstress.

Base bones Seamstress rework ^

Since we used HTML::Seamstress instead of HTML::TreeBuilder, our $tree was blessed as an instance of HTML::Seamstress. Since HTML::Seamstress inherits from HTML::TreeBuilder and HTML::Element::Library, we have a $tree which can use the methods of both.

We will take advantage of the replace_content method in HTML::Element::Library to shorten our program:

<tt>pod_code 'Quickstart/'</tt>

Now of course, this program is just itching to not repeat itself, so we will clean it up just a tad:

<tt>pod_code 'Quickstart/'</tt>

Abstract the file and our operations on it into a Perl LOOM ^

Ok sweet, we have a nice tight program. But is this really application-level code? As the user of ultra-scaffolded frameworks such as Class::DBI and Catalyst, I can say no. Our inline code must be much tighter. It must do no more than use, new, and operation() whatever operation() may be.

The key abstraction technique of the uber-modules is a package. Normally a package collects together a set of methods. In our case, it is collecting together an HTML file and the object-oriented operations on it. alert, alert: acronym, alert from this point forward, a Perl class abstracting a file and tree operations on the file will be called a LOOM - (L)ibrary (O)f (O)bject-oriented (M)ethods for HTML files.

On the whole, there are two ways to build a LOOM. The quick and dirty way is to stick a .pm file in the same directory as the html file. This is fine for most purposes and is what I like to use.

However in some cases it is not desirable or possible for the HTML and Perl to be in the same directory. This is the slow and clean approach, which does have some additional advantages which will be discussed.

Quick and dirty LOOM building: .pm and .html in same directory

We have an html::Greeting module like this:

<tt>pod_code 'Quickstart/html/'</tt>

which we make nice tight application-level use of like this:

<tt>pod_code 'Quickstart/'</tt>

Cleaning up our Perl class

We are flowing smoothly now with nice tight code in our application. But should we be happy with this module? I see a few drawbacks which require improvement:

Let's fix the first problem first.

Make path to HTML file absolute

Again, Seamstress just happens to have a subroutine which guesses the name of the HTML file associated with a Seamstress-style Perl module. It is called html() and here we see it in use to give us the path to our file in absolute fashion:

<tt>pod_code 'Quickstart/html/'</tt>

and main code body is still the same:

<tt>pod_code 'Quickstart/'</tt>

Slow and clean LOOM building: .pm and .html in different directory

Here we need to slip a class in between HTML::Seamstress and our LOOM:

<tt>pod_code 'Quickstart/lib/HTML/Seamstress/'</tt>

This class will make it easy to track down the directory of our HTML files.

The LOOM class inherits from it and makes use of it in its constructor:

<tt>pod_code 'Quickstart/lib/html/'</tt>

And out main body code is just as tight. We have a few statements to make sure to use the right version of html::Greeting, but other than that, no changes:

<tt>pod_code 'Quickstart/'</tt>

Slow and clean has extra programming advantages

Slow and clean is not just a different way to do the same thing. By creating a local base class, you have full control over how to connect an HTML file to your Perl code.

Your HTML designer can have his files mounted elsewhere. And you dont

And being infection-free is the way I like it.. in Perl and uhhh... other endeavors.

Not recommended slow clean way: Inline the HTML

There is no Seamstress API or utility support for this. But it is an idea and I just wanted to mention it for completeness. You can create a .pm with the HTML along the lines of this.

 package html::hello_world;

 sub new {...}

 sub process {...} 



And then you could use File::Slurp to read it in and submit an appropriate HTML::Seamstress::new_from_content() method to do the proper blessings.

But I don't like this approach. It makes it hard to stay synchronized with the designer as he continually makes updates.

Automated creation of Seamstress-style packages ^

Instead of manually creating or copying and pasting packages to create Seamstress-style packages, the script in the Seamstress was off use. It is designed to help build the slow-clean LOOMs not the quick-and-dirty ones.... it really should be updated to support either usage mode.

Tips for effective Seamstress use ^

Use subroutines and Params::Validate to "componentize" your operations

The final phase in Seamstress best practices is to break each tree manipulation down into a separate subroutine whose parameters are specified by Params::Validate.

If you do this, then you can control the dynamic HTML generation by parameterizing your subs properly. This advice will make more sense as you do more complex things with Seamstress

Now you're ready for the big time! Have fun!

Identify HTML elements by class tags if you plan to loop them

If your dummy HTML has a section which will be used as a sample and cloned repeatedly (either by you manually or by an HTML::Element::Library method), then locate it by a class tag and do not assign it an id tag. This is because HTML becomes invalid when an id tag appears more than once in the same document.

For example here is some Template code:

 [% FOR column = item.columns('view') %]
    <b class="title">[% column %]</b><br/>
    [% item.$column %]<br/><br/>
 [% END %]

Here is how I converted it to a Seamstress document:

 <span class="columns_view">
    <b class="title">column_name</b><br/>
    <span class="item_column">column_value</span><br/><br/>


Copyright 2002-2006 by Terrence Brannon.

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

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