NAME

DBIx::Class::Tree::AdjacencyList - Manage a tree of data using the common adjacency list model.

SYNOPSIS

Create a table for your tree data.

  CREATE TABLE employees (
    employee_id INTEGER PRIMARY KEY AUTOINCREMENT,
    parent_id INTEGER NOT NULL DEFAULT 0,
    name TEXT NOT NULL
  );

In your Schema or DB class add Tree::AdjacencyList to the top of the component list.

  __PACKAGE__->load_components(qw( Tree::AdjacencyList ... ));

Specify the column that contains the parent ID of each row.

  package My::Employee;
  __PACKAGE__->parent_column('parent_id');

Optionally, automatically maintane a consistent tree structure.

  __PACKAGE__->repair_tree( 1 );

Thats it, now you can modify and analyze the tree.

  #!/usr/bin/perl
  use My::Employee;

  my $employee = My::Employee->create({ name=>'Matt S. Trout' });

  my $rs = $employee->children();
  my @siblings = $employee->children();

  my $parent = $employee->parent();
  $employee->parent( 7 );

DESCRIPTION

This module provides methods for working with adjacency lists. The adjacency list model is a very common way of representing a tree structure. In this model each row in a table has a prent ID column that references the primary key of another row in the same table. Because of this the primary key must only be one column and is usually some sort of integer. The row with a parent ID of 0 is the root node and is usually the parent of all other rows. Although, there is no limitation in this module that would stop you from having multiple root nodes.

METHODS

parent_column

  __PACKAGE__->parent_column('parent_id');

Declares the name of the column that contains the self-referential ID which defines the parent row. This will create a has_many (children) and belongs_to (parent) relationship.

This method also sets up an additional has_many relationship called parents which is useful when you want to treat an adjacency list as a DAG.

repair_tree

  __PACKAGE__->repair_tree( 1 );

When set a true value this flag causes all changes to a node's parent to trigger an integrity check on the tree. If, when changing a node's parent to one of it's descendents then all its children will first be moved to have the same current parent, and then the node's parent is changed.

So, for example, if the tree is like this:

And you execute:

  $b->parent( $d );

Since D is a descendant of B then all of D's siblings get their parent changed to A. Then B's parent is set to D.

parent

  my $parent = $employee->parent();
  $employee->parent( $parent_obj );
  $employee->parent( $parent_id );

Retrieves the object's parent object, or changes the object's parent to the specified parent or parent ID. If you would like to make the object the root node, just set the parent to 0.

If you are setting the parent then 0 will be returned if the specified parent is already the object's parent and 1 on success.

ancestors

  @list = $employee->ancestors();

Returns a list of ancestors starting with a record's parent and moving toward the tree root.

has_descendant

  if ($employee->has_descendant( $id )) { ... }

Returns true if the object has a descendant with the specified ID.

parents

  my $parents = $node->parents();
  my @parents = $node->parents();

This has_many relationship is not that useful as it will never return more than one parent due to the one-to-many structure of adjacency lists. The reason this relationship is defined is so that this tree type may be treated as if it was a DAG.

children

  my $children_rs = $employee->children();
  my @children = $employee->children();

Returns a list or record set, depending on context, of all the objects one level below the current one. This method is created when parent_column() is called, which sets up a has_many relationship called children.

attach_child

  $parent->attach_child( $child );
  $parent->attach_child( $child, $child, ... );

Sets the child, or children, to the new parent. Returns 1 on success and returns 0 if the parent object already has the child.

siblings

  my $rs = $node->siblings();
  my @siblings = $node->siblings();

Returns either a result set or an array of all other objects with the same parent as the calling object.

attach_sibling

  $obj->attach_sibling( $sibling );
  $obj->attach_sibling( $sibling, $sibling, ... );

Sets the passed in object(s) to have the same parent as the calling object. Returns 1 on success and 0 if the sibling already has the same parent.

is_leaf

  if ($obj->is_leaf()) { ... }

Returns 1 if the object has no children, and 0 otherwise.

is_root

  if ($obj->is_root()) { ... }

Returns 1 if the object has no parent, and 0 otherwise.

is_branch

  if ($obj->is_branch()) { ... }

Returns 1 if the object has a parent and has children. Returns 0 otherwise.

set_primary_key

This method is an override of DBIx::Class' method for setting the class' primary key column(s). This method passes control right on to the normal method after first validating that only one column is being selected as a primary key. If more than one column is then an error will be thrown.

INHERITED METHODS

DBIx::Class

mk_classdata
component_base_class

DBIx::Class::Componentised

inject_base
load_components
load_own_components

Class::Data::Accessor

•: mk_classaccessor

AUTHOR

Aran Clary Deltac <bluefeet@cpan.org>

LICENSE

You may distribute this code under the same terms as Perl itself.