Composite Pattern

Here's an attempt at implementing the Composite Pattern using Hibernate.

http://c2.com/cgi/wiki?CompositePattern

Also see this blog entry for an example using Hibernate Annotations: http://www.researchkitchen.co.uk/blog/archives/57

Hibernate Mapping File

<class name="Site" table="Site">
<id name="id" type="java.lang.Integer" unsaved-value="null">
<generator class="native"/>
</id>

<version name="version" type="long"/>
<set name="childrenSites" inverse="true" lazy="true" cascade="save-update">
<key column="parent"/>
<one-to-many class="Site"/>
</set>
<many-to-one name="parent" column="parent" cascade="save-update" class="Site"/>
<property name="description" type="java.lang.String"/>
<property name="namespace" type="java.lang.String"/>
<property name="name" type="java.lang.String">
</class>

Mysql table generated by running net.sf.hibernate.tool.hbm2java.CodeGenerator.

mysql> desc site;
+-------------+-------------+------+-----+---------+----------------+
| Field       | Type        | Null | Key | Default | Extra          |
+-------------+-------------+------+-----+---------+----------------+
| id          | int(11)     |      | PRI | NULL    | auto_increment |
| version     | bigint(20)  |      |     | 0       |                |
| parent      | int(11)     | YES  | MUL | NULL    |                |
| description | varchar(64) |      |     |         |                |
| namespace   | varchar(64) |      |     |         |                |
| name        | varchar(64) |      |     |         |                |
+-------------+-------------+------+-----+---------+----------------+
6 rows in set (0.03 sec)

Code fragement showing getChildrenSites() and getParent();

List sites = session.find("FROM Site AS site");
System.out.println("Number of sites returned: " + sites.size());
Iterator iter = sites.iterator();
while (iter.hasNext()) {
Site site = (Site) iter.next();
site.getName();
site.getChildrenSites());
site.getParent();
}

NEW COMMENT

Search by subsection	06 Dec 2003, 01:14	pwibbele
I've been playing with a similar structure for another purpose, but have been wondering what the best way to perform a search under a given point in the tree is. I can see a few: 1) Use Lucene and on creation of a site, add all of it's parent sites as metadata to lucene. Unfortunately, this means moving all the metadata when a node or site is relocacted, including adjusting all child nodes when moving a mid-level node. Additionally, it requires a series of traversal steps to find all of the parents, and this may be a series of queries to the database. 2) Store as metadata on the object/table the parent sites of each node. Again, on moving nodes, you have to readjust your metadata. 3) Perform all of your searches by selecting the node under which you want to see the results and traverse. Unfortunately here, it's harder to do a query that returns these results and includes an "and". e.g. "All sites under site X, and with characteristic Y. 4) Limit the heirarchy to one level deep, and thus every child has only one ancestor. While this is restrictive, for some functions, it is suitable. Others?

Multi-level hierarchies	18 Jan 2005, 17:56	gschadow
There are two well known ways to deal with searching in multiple level hierarchies without having to traverse all the links. 1) Interval method: using a low - high interval on each node such that all childrens' intervals are subsets of the parent's interval. 2) Tree-code annotation: as a tree-code attribute (e.g., "1.2.3.4.5") such that you can find all children of "1.2.3" using the predicate treeCode LIKE "1.2.3.%".

Re: Multi-level hierarchies	14 Jul 2005, 06:54	christian
To make searching for it easier, here are the terms usually associated with each technique: >1) Interval method: using a low - high interval on each node such that >all childrens' intervals are subsets of the parent's interval. Nested Set >2) Tree-code annotation: as a tree-code attribute (e.g., "1.2.3.4.5") >such that you can find all children of "1.2.3" using the predicate >treeCode LIKE "1.2.3.%". Materialized Path Typically the weakness of a missing explosion operation in SQL is misused by object database vendors to sell their wares. My blog entry about this issue: http://blog.hibernate.org/cgi-bin/blosxom.cgi/2004/12/04#gettricked