How to implement the query , *.hbm.xml and java about special one-to-one or one-to-none as the below.


There is Cat, Cat could have one child or none child depending on the Child_id value.

The Database table name : Cat

desc Cat;
Id NUMBER NOT NULL UNIQUE;
Name Varchar2(32) NOT NULL;
Child_id NUMBER;


select * from Cat;
Id Name Child_id
-----------------------------------------------------
1000 Kitty 1001
1001 childKitty 1002
1002 grandchildkitty 1003
1003 kitty3 <null>
2000 Polo 1001
2001 Polo2 <null>
3001 Lina <null>

The Child_id relates with Id

What I want to get is that:
If I query Id:1000 (Kitty) once, the all data related could be returned, which includes childKitty and grandchildkitty.

Does anyone tell me how to implement it?








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Hibernate version:3.0.2

Mapping documents:

Code between sessionFactory.openSession() and session.close():

Full stack trace of any exception that occurs:

Name and version of the database you are using: oracle 8.1.7

The generated SQL (show_sql=true):

Debug level Hibernate log excerpt:

Try a one-to-one association with property-ref="childId".



I think you can get this to work.

However, the design would be more flexible, and follow a more common pattern, if a Cat referenced its parent. This allows a Cat to have more than one child. If you need to limit the number of children, that can be done easily in your Java code (the setChildren method would throw an exception if the set has more than one item in it). This is a simple one-to-many relationship.[/code]