NAME

       Extending.pod - How to extend Wiki::Toolkit with your own plugins.

LIMITATIONS

       The extension mechanism is currently only defined for database-backed setups, but since
       nobody has written any other kind of backend I think we're fine for now.

THE SIMPLEST WAY

       You can extend Wiki::Toolkit in a fairly simplified way without the use of plugins, by
       supplying a hash of metadata when you write a node. For example:

         $wiki->write_node( $node, $content, $checksum,
                            { postcode => $postcode }   );

       and on node retrieval you'll get it back again:

         my %node = $wiki->retrieve_node( $node );
         my $postcode = $node{metadata}{postcode}[0];

       You can supply more than one value for each type of metadata:

         $wiki->write_node( $node, $content, $checksum,
             { postcode => "W6 9PL",
               category => [ "Thai Food", "Restaurant", "Hammersmith" ] } );

       And get back a list of nodes which have a given value for a given metadata type:

         my @nodes = $wiki->list_nodes_by_metadata(
             metadata_type  => "category",
             metadata_value => "Hammersmith" );

       For anything more complicated you will need to write a plugin.

PLUGIN BASE CLASS

       Plugins should inherit from "Wiki::Toolkit::Plugin". This base class provides the
       following methods to give access to a "Wiki::Toolkit" object's backends:

       •   "datastore" - returns the store object

       •   "indexer" - returns the search object

       •   "formatter" - returns the formatter object

       If you want these methods to return anything useful then call

         $wiki->register_plugin( plugin => $plugin);

       before calling say

         my %node_data = $plugin->datastore->retrieve_node( "Foo" );

CALLING API

         my $plugin = Wiki::Toolkit::Plugin::Foo->new( ...any required args... );
         $wiki->register_plugin( plugin => $plugin );

         $wiki->write_node( "Test Node" ,"Test", $checksum,
                            { foo_data => { a => "apple",
                                            b => "banana" }
                            } );

         my $bee = $plugin->get_word( node => "Test Node", letter => "b" );

       or

         my $plugin = OpenGuides::London::Underground->new;
         $wiki->register_plugin( plugin => $plugin );
         $wiki->write_node( "Hammersmith Station", "a station", $checksum,
                            { tube_data => [
                                { line => "Piccadilly",
                                  direction => "Eastbound",
                                  next_station => "Baron's Court Station"
                                },
                                { line => "Piccadilly",
                                  direction => "Westbound",
                                  next_station => "Acton Town Station"
                                }
                                           ]
                             }
                           );

         # Put more data in, then

         my @route = $plugin->find_route( from => "Holborn Station",
                                          to   => "Acton Town Station" );

STORE ACCESS

       A plugin named Wiki::Toolkit::Plugin::Foo may access the backend database directly like
       so:

       •   Read-only access to any table

       •   Read-write access to any table whose name begins with "p_" .
           $Wiki::Toolkit::Plugin::Foo::plugin_key . "_"

           $Wiki::Toolkit::Plugin::Foo::plugin_key should be different from the keys of all other
           plugins. No, I haven't set anything up to ensure this.

REQUIREMENTS FOR PLUGIN AUTHORS

       Either be database-agnostic, or state clearly in your docs which databases you support,
       and handle errors nicely.  Be aware that non-database backends may exist in the future.

       Be aware of whether you need to check for locks explicitly in different databases (see
       code of Wiki::Toolkit::Store::* to find out).

REQUIRED METHODS

       on_register
           Check that any tables you require are set up, and set them up if not.

OPTIONAL METHODS

       post_write
           This will be called every time a node is written, with the arguments like so:

             $plugin->post_write( node     => $node_name,
                                  version  => $version_number,
                                  content  => $content,
                                  metadata => \%user_defined_metadata );

           This will happen after the node data is all written, but before any lock is released.

           We could probably reimplement the searches as plugins like this if we want to, but
           this will require writing extra backends for Search::InvertedIndex so it can work
           within the same database.

           The user-defined metadata will already have been stored in the backend but it is
           available here for you to do what you will with it.

           Its return value should be true on success and false on error.

       post_read
           THIS IS NOT YET IMPLEMENTED.

           This will be called every time a node is read, with the arguments like so:

             $plugin->post_read( node     => $node_name,
                                 version  => $version_number,
                                 content  => $content,
                                 metadata => \%user_defined_metadata );

           It cannot affect the data returned to the caller. It should be used for its side-
           effects, for example tracking the number of times a given node is accessed.

           Its return value should be true on success and false on error.

PLUGIN CONFLICTS

       What if we have more than one plugin registered? What if we change the mechanism to allow
       the plugins to change the data stored in the database/returned to the caller?