Hi,

My task is to provide Hibernate-based access layer to a legacy database and no changes are allowed to the schema. This creates few challenges in describing Hibernate mapping. Being a beginner in Hibernate I am looking for a help from this forum.

I need to describe one-to-many relationship between parent table PARENT and child table CHILD. In the Java layer it is modelled as collection of Child elements in Parent class. Child table has foreign key FK_PARENT which links it to a primary key of parent table KEY. But join also has an additional constraint. Both tables have column SEQ_NUM and join must be done with the following condition: PARENT.KEY = CHILD.FK_PARENT and PARENT.SEQ_NUM = CHILD.SEQ_NUM.

Hibernate allows describe collection of children related by foreign key only (at least it’s my understanding of Hibernate documentation and DTD). Looks like the only option for additional constraint would be to use attribute “where”, but I am not sure if Hibernate would allow constraint in the following form: where=” PARENT.SEQ_NUM = CHILD.SEQ_NUM”.

Any help would be appreciated,
Thanks

There are three things you can do.

The legal way is to do a subselect:




Which is quite performance inefficient. Second option is write a custom loader which is both legal and efficient. The third option is to use hibernate generated aliases in the where property:




if you are wondering what the alias is going to be you need to run hibernate once and see the generated sql. However, this is cheating and since cheating is not a good thing you will be nailed at some point some how. So use this at your own responsibility or make sure you leave the company before they decide to upgrade hibernate jars.


Farzad-