Doctrine_manual-1-2-en

Chapter 18: Hierarchical Data 278
of a root node and so on. By reading the level field from your nodes you can easily display
your tree with proper indention.
You must never assign values to lft, rgt, level. These are managed transparently by the
nested set implementation.
Multiple Trees
The nested set implementation can be configured to allow your table to have multiple root
nodes, and therefore multiple trees within the same table.
The example below shows how to setup and use multiple roots with the Category model:
Listing
18-3
// models/Category.php
class Category extends Doctrine_Record
{
// ...
}
public function setUp()
{
$options = array(
'hasManyRoots' => true,
'rootColumnName' => 'root_id'
);
$this->actAs('NestedSet', $options);
}
Here is the same example in YAML format. You can read more about YAML in the YAML
Schema Files (page 195) chapter:
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18-4
---
# schema.yml
# ...
Category:
actAs:
NestedSet:
hasManyRoots: true
rootColumnName: root_id
columns:
name: string(255)
The rootColumnName is the column used to differentiate between trees. When you create a
new root node you have the option to set the root_id manually, otherwise Doctrine will
assign a value for you.
In general use you do not need to deal with the root_id directly. For example, when you
insert a new node into an existing tree or move a node between trees Doctrine transparently
handles the associated root_id changes for you.
Working with Trees
After you successfully set up your model as a nested set you can start working with it.
Working with Doctrine's nested set implementation is all about two classes:
Doctrine_Tree_NestedSet and Doctrine_Node_NestedSet. These are nested set
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