NAME

DBIx::Class::MaterializedPath - efficiently retrieve and search trees with DBIx::Class

VERSION

version 0.002001

SYNOPSIS

package A::Schema::Result::Category;

use strict;
use warnings;

use base 'DBIx::Class::Core';

__PACKAGE__->table('category');

__PACKAGE__->load_components('MaterializedPath');

__PACKAGE__->add_columns(
   id => {
      data_type => 'int',
      is_auto_increment => 1,
   },

   parent_id => {
      data_type => 'int',
      is_nullable => 1, # root
   },

   parent_path => {
      data_type => 'varchar',
      size      => 256,
      is_nullable => 1,
   },

   name => {
      data_type => 'varchar',
      size      => 256,
   },
);

__PACKAGE__->set_primary_key('id');

__PACKAGE__->belongs_to(
  parent_category => 'A::Schema::Result::Category', 'parent_id'
);

__PACKAGE__->has_many(
  child_categories => 'A::Schema::Result::Category', 'parent_id'
);

sub materialized_path_columns {
   return {
      parent => {
         parent_column                => 'parent_id',
         parent_fk_column             => 'id',
         materialized_path_column     => 'parent_path',
         include_self_in_path         => 1,
         include_self_in_reverse_path => 1,
         separator                    => '/',
         parent_relationship          => 'parent_category',
         children_relationship        => 'child_categories',
         full_path                    => 'ancestors',
         reverse_full_path            => 'descendants',
      },
   }
}

1;

Elsewhere...

my $child_rows = $row->descendants;

or better yet

my $awesome_kids = $rs->search({ awesome => 1 })
  ->related_resultset('descendants');

DESCRIPTION

Materialized path is a way to store trees in relational databases that results in very efficient retrieval, at the expense of space and more write-time queries.

This module makes using matpaths easy. The interface is somewhat unusual, but the benefit is that it creates actual relationships for the both directions of the tree, allowing you to use the powerful querying DBIx::Class already gives you.

The first strange part of the interface is that the call to load_components must come after the call to table. The next strange bit is that the way you define all of the metadata about your matpath is by defining a subroutine called materialized_path_columns. The subroutine must return a hashref where the key is name of your path (currently unused) and the value is the metadata for the path. Here are the parts that need to be defined in the metadata:

• parent_column - the column that points directly to the parent row, for example parent_id.

• parent_fk_column - the column that parent_column points to, for example id.

• materialized_path_column - the column that contains the materialized path. One thing to note here is that the width of the column defines how deep your tree can be. For example if the number of digits for most of your id's is three, and your materialized path column is 255 characters wide, you can support a depth of something like 63 levels, because each level in the tree is q(/) . "$id", so 255/4 ~~ 63. An example for this might be parent_materialized_path.

• parent_relationship - the direct relationship to your parent row

• children_relationship - the direct relationship to your child rows

• full_path - the name of the relationship that this materialized path will define for all parents. For example, ancestry.

• reverse_full_path - the name of the relationship that this materialized path will define for all children. For example, descendants.

• include_self_in_path - (optional) I've found that it's often helpful to include the current row in the full ancestry. For example if your path is a for categorization system you probably want to turn this on.

• include_self_in_reverse_path - (optional) see above, but for chilren instead of parents

• separator - (optional) defaults to /. If you don't know what this is for just ignore it.

AUTHOR

Arthur Axel "fREW" Schmidt <frioux+cpan@gmail.com>

COPYRIGHT AND LICENSE

This software is copyright (c) 2014 by Arthur Axel "fREW" Schmidt.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.