Doctrine_manual-1-2-en

Chapter 18: Hierarchical Data 277
Nested Set
Introduction
Nested Set is a solution for storing hierarchical data that provides very fast read access.
However, updating nested set trees is more costly. Therefore this solution is best suited for
hierarchies that are much more frequently read than written to. And because of the nature of
the web, this is the case for most web applications.
For more detailed information on the Nested Set, read here:
• http://www.sitepoint.com/article/hierarchical-data-database/2 33
• http://dev.mysql.com/tech-resources/articles/hierarchical-data.html 34
Setting Up
To set up your model as Nested Set, you must add some code to the setUp() method of your
model. Take this Category model below for example:
// models/Category.php
Listing
18-1
class Category extends Doctrine_Record
{
public function setTableDefinition()
{
$this->hasColumn('name', 'string', 255);
}
}
public function setUp()
{
$this->actAs('NestedSet');
}
Here is the same example in YAML format. You can read more about YAML in the YAML
Schema Files (page 195) chapter:
---
# schema.yml
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18-2
# ...
Category:
actAs: [NestedSet]
columns:
name: string(255)
Detailed information on Doctrine's templating model can be found in chapter 16 Behaviors
(page 239). These templates add some functionality to your model. In the example of the
nested set, your model gets 3 additional fields: lft, rgt and level. You never need to care
about the lft and rgt fields. These are used internally to manage the tree structure. The
level field however, is of interest for you because it's an integer value that represents the
depth of a node within it's tree. A level of 0 means it's a root node. 1 means it's a direct child
33. http://www.sitepoint.com/article/hierarchical-data-database/2
34. http://dev.mysql.com/tech-resources/articles/hierarchical-data.html
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