--- name: "DBIx::Class::Tree::NestedSet" section: "3pm" platform: "linux" package: "libdbix-class-tree-nestedset-perl" version: "0.10-1.1" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/DBIx::Class::Tree::NestedSet" --- # DBIx::Class::Tree::NestedSet(3pm) Manage trees of data using the nested set model ## NAME DBIx::Class::Tree::NestedSet - Manage trees of data using the nested set model ## SYNOPSIS Create a table for your tree data. ``` CREATE TABLE Department ( id INTEGER PRIMARY KEY AUTOINCREMENT, root_id integer, lft integer NOT NULL, rgt integer NOT NULL, level integer NOT NULL, name text NOT NULL, ); ``` In your Schema or DB class add Tree::NestedSet to the top of the component list. ``` __PACKAGE__->load_components(qw( Tree::NestedSet ... )); ``` Specify the columns required by the module. ``` package My::Department; __PACKAGE__->tree_columns({ root_column => 'root_id', left_column => 'lft', right_column => 'rgt', level_column => 'level', }); ``` Using it: ``` my $root = My::Department->create({ ... }); my $child = $root->add_to_children({ ... }); my $rs = $root->children; my @descendants = $root->children; my $parent = $child->parent; my $rs = $child->ancestors; my @ancestors = $child->ancestors; ``` ## DESCRIPTION This module provides methods for working with nested set trees. The nested tree model is a way of representing hierarchical information in a database. This takes a different approach to the Adjacency List implementation. (see DBIx::Class::Tree::AdjacencyList which uses `"parent"` relationships in a recursive manner. The NestedSet implementation can be more efficient for most searches than the Adjacency List Implementation, for example, to obtain all descendants requires recursive queries in the Adjacency List implementation but is a single query in the NestedSet implementation. The trade-off is that NestedSet inserts are more expensive so it is most useful if you have an application that does many reads but few inserts. More about NestedSets can be found at \ Oh, and although I give some code examples of familial relationships (where there are usually two parents), both Adjacency List and NestedSet implementations can only have one parent. ## RELATIONS This module automatically creates several relationships. ### root ``` $root_node = $node->root; ``` A belongs\_to relation to the root of `$node`s tree. ### nodes ``` $all_nodes = $node->nodes; $new_node = $node->add_to_nodes({name => 'Mens Wear'}); ``` A has\_many relationship to all the nodes of `$node`s tree. Adding to this relationship creates a rightmost child to `$node`. ### parent ``` $parent = $node->parent; ``` A belongs\_to relationship to the parent node of `$node`s tree. Note that only the root node does not have a parent. ### children ``` $rs = $node->children; @children = $node->children; $child = $node->add_to_children({name => 'Toys'}); ``` A has\_many relation to the children of `$node`. Adding to this relationship creates a rightmost child to `$node`. ### descendants ``` $rs = $node->descendants; @descendants = $node->descendants; $child = $node->add_to_descendants({name => 'Mens Wear'}); ``` A has\_many relation to the descendants of `$node`. Adding to this relationship creates a rightmost child to `$node`. ### ancestors ``` $rs = $node->ancestors; @ancestors = $node->ancestors; $parent = $node->add_to_ancestors({name => 'Head office'}); ``` A has\_many relation to the ancestors of `$node`. Adding to this relationship creates a new node in place of `$node` and makes it the parent of `$node`. All descendants of `$node` will likewise be pushed town the hierarchy. ## METHODS Many methods have alternative names, e.g. `"left_siblings"` and `"previous_siblings"` This is in deference to the DBIx::Class::Ordered module which uses terms `"previous"` `"next"` `"first"` and `"last"`. Similarly DBIx::Class::Tree::AdjacencyList::Ordered uses terms `"append"`, `"prepend"`, `"before"` and `"after"` However, my preference to use terms `"left"` and `"right"` consistently when using this module. However, the other names are available if you are more familiar with those modules. ### tree\_columns ``` __PACKAGE__->tree_columns({ left_column => 'lft', right_column => 'rgt', root_column => 'root_id', level_column => 'level', }); ``` Declare the name of the columns defined in the database schema. None of these columns should be modified outside if this module. left\_column and right\_column are unlikely to be of any use to your application. They should be integer fields. Multiple trees are allowed in the same table, each tree will have a unique value in the root\_column. In the current implementation this should be an integer field The level\_column may be of use in your application, it defines the depth of each node in the tree (with the root at level zero). ### create ``` my $tree = $schema->resultset('My::Department')->create({ name = 'Head Office', }); my $tree = $schema->resultset('My::Department')->create({ name = 'UK Office', root_id = $uk_office_ident, }); ``` Creates a new root node. If the root\_column (root\_id) is not provided then it defaults to producing a node where the root\_column has the same value as the primary key. This will croak if the table is defined with multiple key primary index. Note that no checks (yet) are made to stop you creating another key with the same root\_id as an existing tree. If you do so you will get into a terrible mess! ### delete ``` $department->delete; ``` This will delete the node and all descendants. Cascade Delete is turned off in the has\_many relationships `"nodes"` `"children"` `"descendants"` so that delete DTRT. ### is\_root ``` if ($node->is_root) { print "Node is a root\n"; } ``` Returns true if the `$node` is a root node ### is\_branch ``` $has_children = $node->is_branch; ``` Returns true if the node is a branche (i.e. has children) ### is\_leaf ``` $is_terminal_node = $node->is_leaf; ``` Returns true if the node is a leaf (i.e. it has no children) ### siblings ``` @siblings = $node->siblings; $siblings_rs = $node->siblings; ``` Returns all siblings of this `$node` excluding `$node` itself. Since a root node has no siblings it returns undef. ### left\_siblings (or previous\_siblings) ``` @younger_siblings = $node->left_siblings; $younger_siblings_rs = $node->left_siblings; ``` Returns all siblings of this `$node` to the left this `$node`. Since a root node has no siblings it returns undef. ### right\_siblings (or next\_siblings) ``` @older_siblings = $node->right_siblings; $older_siblings_rs = $node->right_siblings; ``` Returns all siblings of this `$node` to the right of this `$node`. Since a root node has no siblings it returns undef. ### left\_sibling (or previous\_sibling) ``` $younger_sibling = $node->left_sibling; ``` Returns the sibling immediately to the left of this `$node` (if any). ### right\_sibling (or next\_sibling) ``` $older_sibling = $node->right_sibling; ``` Returns the sibling immediately to the right of this `$node` (if any). ### leftmost\_sibling (or first\_sibling) ``` $youngest_sibling = $node->leftmost_sibling; ``` Returns the left most sibling relative to this `$node` (if any). Does not return this `$node` if this node is the leftmost sibling. ### rightmost\_sibling (or last\_sibling) ``` $oldest_sibling = $node->rightmost_sibling; ``` Returns the right most sibling relative to this `$node` (if any). Does not return this `$node` if this node is the rightmost sibling. ### CREATE METHODS The following create methods create a new node in relation to an existing node. ### create\_right\_sibling ``` $bart->create_right_sibling({ name => 'Lisa' }); ``` Create a new node as a right sibling to `$bart`. ### create\_left\_sibling ``` $bart->create_left_sibling({ name => 'Maggie' }); ``` Create a new node as a left sibling to `$bart`. ### create\_rightmost\_child ``` $homer->create_rightmost_child({ name => 'Lisa' }); ``` Create a new node as a rightmost child to `$homer` ### create\_leftmost\_child ``` $homer->create_leftmost_child({ name => 'Maggie' }); ``` Create a new node as a leftmost child to `$homer` ### ATTACH METHODS The following attach methods take an existing node (and all of it's descendants) and attaches them to the tree in relation to an existing node. The node being inserted can either be from the same tree (as identified by the root\_column) or from another tree. If the root of another tree is attached then the whole of that tree becomes a sub-tree of this node's tree. The only restriction is that the node being attached cannot be an ancestor of this node. When attaching multiple nodes we try to DWIM so that the order they are specified in the call represents the order they appear in the siblings list. e.g. if we had a parent with children A,B,C,D,E and we attached nodes 1,2,3 in the following calls, we expect the following results. ``` $parent->attach_rightmost_child 1,2,3 gives us children A,B,C,D,E,1,2,3 $parent->attach_leftmost_child 1,2,3 gives us children 1,2,3,A,B,C,D,E $child_C->attach_right_sibling 1,2,3 gives us children A,B,C,1,2,3,D,E $child_C->attach_left_sibling 1,2,3 gives us children A,B,1,2,3,C,D,E $child_C->attach_rightmost_sibling 1,2,3 gives us children A,B,C,D,E,1,2,3 $child_C->attach_leftmost_sibling 1,2,3 gives us children 1,2,3,A,B,C,D,E ``` ### attach\_rightmost\_child (or append\_child) ``` $parent->attach_rightmost_child($other_node); $parent->attach_rightmost_child($other_node_1, $other_node_2, ...); ``` Attaches the other\_nodes to `$parent` as the rightmost children. ### attach\_leftmost\_child ``` $parent->attach_leftmost_child($other_node); $parent->attach_leftmost_child($other_node_1, $other_node_2, ...); ``` Attaches the other\_nodes to `$parent` as the leftmost children. ### attach\_right\_sibling (or attach\_after) ``` $node->attach_right_sibling($other_node); $node->attach_right_sibling($other_node_1, $other_node_2, ...); ``` Attaches the other\_nodes to `$node` as it's siblings. ### attach\_left\_sibling ``` $node->attach_left_sibling($other_node); $node->attach_left_sibling($other_node_1, $other_node_2, ...); ``` Attaches the other\_nodes to `$node` as it's left siblings. ### attach\_rightmost\_sibling ``` $node->attach_rightmost_sibling($other_node); $node->attach_rightmost_sibling($other_node_1, $other_node_2, ...); ``` Attaches the other\_nodes to `$node` as it's rightmost siblings. ### attach\_leftmost\_sibling ``` $node->attach_leftmost_sibling($other_node); $node->attach_leftmost_sibling($other_node_1, $other_node_2, ...); ``` Attaches the other\_nodes to `$node` as it's leftmost siblings. ### move\_left (or move\_previous) ``` $node->move_left; ``` Exchange the `$node` with the sibling immediately to the left and return the node it exchanged with. If the `$node` is already the leftmost node then no exchange takes place and the method returns undef. ### move\_right (or move\_next) ``` $node->move_right; ``` Exchange the `$node` with the sibling immediately to the right and return the node it exchanged with. If the `$node` is already the rightmost node then no exchange takes place and the method returns undef. ### move\_leftmost (or move\_first) ``` $node->move_leftmost; ``` Exchange the `$node` with the leftmost sibling and return the node it exchanged with. If the `$node` is already the leftmost node then no exchange takes place and the method returns undef. ### move\_rightmost (or move\_last) ``` $node->move_rightmost; ``` Exchange the `$node` with the rightmost sibling and return the node it exchanged with. If the `$node` is already the rightmost node then no exchange takes place and the method returns undef. ### CUTTING METHODS ### take\_cutting Cuts the invocant and its descendants out of the tree they are in, making the invocant the root of a new tree. Returns the modified invocant. ### dissolve Dissolves the entire thread, that is turn each node of the thread into a single-item tree of its own. ## CAVEATS ### Multiple Column Primary Keys Support for Multiple Column Primary Keys is limited (mainly because I rarely use them) but I have tried to make it possible to use them. Please let me know if this does not work as well as you expect. ### discard\_changes By the nature of Nested Set implementations, moving, inserting or deleting nodes in the tree will potentially update many (sometimes most) other nodes. Even if you have preloaded some of the objects, if you make a change to one object the other objects will not reflect their new value until you have reloaded them from the database. (see "discard\_changes" in DBIx::Class::Row) A simple demonstration of this ``` $grampa = $schema->schema->resultset('Simpsons')->create({ name => 'Abraham' }); $homer = $grampa->add_children({name => 'Homer'}); $bart = $homer->add_children({name => 'Bart'}); ``` The methods in this module will do their best to keep instances that they know about updated. For example the first call to `"add_children"` in the above example will update `$grampa` and `$homer` with the latest changes to the database. However, the second call to `"add_children"` only knows about `$homer` and `$bart` and in adding a new node to the tree it will update the `$grampa` node in the database. To ensure you have the latest changes do the following. ``` $grampa->discard_changes. ``` Not doing so will have unpredictable results. ## AUTHORS Code by Ian Docherty \ Based on original code by Florian Ragwitz \ Incorporating ideas and code from Pedro Melo \ Special thanks to Moritz Lenz who sent in lots of patches and changes for version 0.08 ## COPYRIGHT AND LICENSE Copyright (c) 2009-2011 The above authors This is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.10.0 or, at your option, any later version of Perl 5 you may have available.