Christopher H. Laco > Apache-AxKit-Language-XSP-ObjectTaglib-0.09000 > Apache::AxKit::Language::XSP::ObjectTaglib

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Module Version: 0.09000   Source  

NAME ^

Apache::AxKit::Language::XSP::ObjectTaglib - Helper for OO Taglibs

SYNOPSIS ^

    package MyTaglib;
    use strict;
    use warnings;
    use base 'Apache::AxKit::Language::XSP::ObjectTaglib';
    use vars qw(@specification);

    @specification = (
        ...
    );

DESCRIPTION ^

This is an AxKit tag library helper for easily wrapping object-oriented classes into XSP tags. The interface to the class is through a specification which your taglib provides as a package variable. You may wrap single or multiple classes within the same taglib, iterate over several objects, and call methods on a given object.

Here is a sample specification:

    @specification = (
      {
        tag     => 'name',
        context => 'resources',
        target  => 'resource'
      }, {
        tag      => 'resources',
        target   => 'course',
        type     => 'loop',
        iterator => 'resource'
      }, {
        tag   => 'courses',
        type  => 'special',
        start => \&start_courses,
        end   => \&end_courses
      }, {
        tag    => 'name',
        target => 'course'
      }, {
        tag    => 'code',
        target => 'course'
      }, {
        tag    => 'description',
        target => 'course',
        type   => 'as_xml'
      }, {
        tag    => 'summary',
        target => 'course',
        type   => 'as_xml'
      }, {
        tag      => 'presentations',
        target   => 'course',
        type     => 'loop',
        iterator => 'presentation'
      }, {
        tag    => 'size',
        key    => 'calculateSize',
        target => 'presentation',
        notnull => 1
      }, {
        tag      => 'prerequisites',
        target   => 'course',
        type     => 'loop',
        iterator => 'course'
      }
    );

This is the specification used in the sample AxKit::XSP::ObjectTaglib::Demo Taglib so all variable names used in the examples below start with _xsp_axkit_xsp_objecttaglib_demo_. Here's what this means:

      {
        tag     => 'name',
        context => 'resources',
        target  => 'resource'
      }, {

Define a tag called name which occurs inside of another tag called resources. (We'll define a top-level name tag for courses later, so this context-sensitive override has to come first.) When this tag is seen, the method name will be called on the variable @_xsp_axkit_xsp_objecttaglib_demo_resource.

      }, {
        tag      => 'resources',
        target   => 'course',
        type     => 'loop',
        iterator => 'resource'
      }, {

Define a tag called resources that will loop through each resource returned by the method resources on the course object. When combined with the first defined tag, the code generated looks something like this:

    for $_xsp_axkit_xsp_objecttaglib_demo_resource
      ($_xsp_axkit_xsp_objecttaglib_demo_course->resources) {
      $_xsp_axkit_xsp_objecttaglib_demo_course->name;
    };

Now, on the main looping tag courses.

      }, {
        tag   => 'courses',
        type  => 'special',
        start => \&start_courses,
        end   => \&end_courses
      }, {

courses will be the main entry point for our tag library, and as such needs to do some special things to set itself up. Hence, it uses a special type, and provides its own handlers to handle the start and end tag events. These handlers will be responsible for setting up $_xsp_axkit_xsp_objecttaglib_demo_courses, used in the following tags, and looping over the possible courses, setting $_xsp_axkit_xsp_objecttaglib_demo_course appropriately.

      }, {
        tag    => 'name',
        target => 'course'
      }, {
        tag    => 'code',
        target => 'course'
      }, {
        tag    => 'description',
        target => 'course',
        type   => 'as_xml'
      }, {
        tag    => 'summary',
        target => 'course',
        type   => 'as_xml'
      }, {

When we see the name tag, we call the name method on each $_xsp_axkit_xsp_objecttaglib_demo_course object within the loop. Similarly, the code tag calls the code method on the same object.

The description and summary tags call the description and summary methods on each course object with the loop, this time making sure that the result is valid XML instead of plain text. (This is because we store the description in the database as XML, and don't want it escaped before AxKit throws it onto the page.)

      }, {
        tag      => 'presentations',
        target   => 'course',
        type     => 'loop',
        iterator => 'presentation'
      }, {

Each course object has a presentations method, which is wrapped by the presentations tag. This method returns a list of objects representing the presentations of a course; the presentations tag sets up a loop, with $_xsp_axkit_xsp_objecttaglib_demo_presentation as the iterator. Hence, inside of a presentations tag, target => "presentation" will cause the method to be called on each presentation object in turn.

      }, {
        tag    => 'size',
        key    => 'calculateSize',
        target => 'presentation',
        notnull => 1
      }, {

Like the course name tag, we'll declare a size tag for the presentation object.

      }, {
        tag      => 'prerequisites',
        target   => 'course',
        type     => 'loop',
        iterator => 'course'
      }

This is slightly dirty. We want a prerequisites tag to refer to other course objects, namely, the courses which are required for admission to the current course. ie:

    <demo:prerequisites>
      <prerequisite>
        <name><demo:name/></name>
        <code><demo:code/></code>
      </prerequisite>
    </demo:prerequisites>

So when we see the prerequisites tag, we call the prerequisites method on our course target, $_xsp_axkit_xsp_coursebooking_course. This returns a list of new prerequisite objects, which we loop over. (type = "loop">)

Our loop iterator will be $_xsp_axkit_xsp_objecttaglib_demo_course itself, so the other tags will work properly on the iterated courses.

Some code is worth a thousand words. The generated perl will look something like this:

    for my $_xsp_axkit_xsp_objecttaglib_demo_course
        ($_xsp_axkit_xsp_objecttaglib_demo_course->prerequisites) {
        ... $_xsp_axkit_xsp_objecttaglib_demo_course->name ...
    }

Because we want to use the name tag within the prerequisites and the courses, we chose the slightly dirty method above. We could also have declared a new tag called reqname and chosen a cleaner iterator like so

      }, {
        tag      => 'prerequisites',
        target   => 'course',
        type     => 'loop',
        iterator => 'prerequisite'
      }, {
        tag      => 'reqname',
        target   => 'prerequisite'
      }

and then use slightly different XSP like this

    <demo:prerequisites>
      <prerequisite>
        <name><demo:reqname/></name>
        <code><demo:code/></code>
      </prerequisite>
    </demo:prerequisites>

Here's another quick example:

    our @specification = (
        { tag => "person", type => "special",
                            start => \&start_person, end => \&end_person },
        { tag => "name", key => "cn", target => 'person'},
        ...
    );

This comes from a wrapper around LDAP. As before, the person tag at the top level has two subroutines to set up the person target. (which in this case will be $_xsp_axkit_xsp_ldap_person) When a name tag is seen inside of the person tag, a method is called on that target. This time, we use key to say that the method name is actually cn, rather than name. Hence the following XSP:

    <b:person dn="foo">
       <b:name/>
    </b:person>

generates something like this:

    {
    my $_xsp_axkit_xsp_ldap_person = somehow_get_ldap_object(dn => "foo");

       ...
       $_xsp_axkit_xsp_ldap_person->cn();
       ...
    }

All clear?

SEE ALSO ^

AxKit::XSP::ObjectTaglib::Demo

AUTHOR ^

    Christopher H. Laco
    CPAN ID: CLACO
    claco@chrislaco.com
    http://today.icantfocus.com/blog/

AUTHOR EMERITUS ^

The original version was created by Simon Cozens.

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