Hibernate3: Self-Referencing Objects
- by monojohnny
Need some help on understanding how to do this; I'm going to be running recursive 'find' on a file system and I want to keep the information in a single DB table - with a self-referencing hierarchial structure:
This is my DB Table structure I want to populate.
DirObject Table:
id int NOT NULL,
name varchar(255) NOT NULL,
parentid int NOT NULL);
Here is the proposed Java Class I want to map (Fields only shown):
public DirObject {
int id;
String name;
DirObject parent;
...
For the 'root' directory was going to use parentid=0; real ids will start at 1, and ideally I want hibernate to autogenerate the ids.
Can somebody provide a suggested mapping file for this please; as a secondary question I thought about doing the Java Class like this instead:
public DirObject {
int id;
String name;
List<DirObject> subdirs;
Could I use the same data model for either of these two methods ? (With a different mapping file of course).
--- UPDATE: so I tried the mapping file suggested below (thanks!), repeated here for reference:
<hibernate-mapping>
<class name="my.proj.DirObject" table="category">
...
<set name="subDirs" lazy="true" inverse="true">
<key column="parentId"/>
<one-to-many class="my.proj.DirObject"/>
</set>
<many-to-one name="parent"
class="my.proj.DirObject"
column="parentId" cascade="all" />
</class>
...and altered my Java class to have BOTH 'parentid' and 'getSubDirs' [returning a 'HashSet'].
This appears to work - thanks, but this is the test code I used to drive this - I think I'm not doing something right here, because I thought Hibernate would take care of saving the subordinate objects in the Set without me having to do this explicitly ?
DirObject dirobject=new DirObject();
dirobject.setName("/files");
dirobject.setParent(dirobject);
DirObject d1, d2;
d1=new DirObject(); d1.setName("subdir1"); d1.setParent(dirobject);
d2=new DirObject(); d2.setName("subdir2"); d2.setParent(dirobject);
HashSet<DirObject> subdirs=new HashSet<DirObject>();
subdirs.add(d1);
subdirs.add(d2);
dirobject.setSubdirs(subdirs);
session.save(dirobject);
session.save(d1);
session.save(d2);
