I have a database table that has no primary key defined. I cannot change the schema. But a combination of four columns can uniquely identify each record. The problem is that three of the columns could be null.

Typical records are:
-----------------------------
column1 column2 column3 column4
a001 null null null
a001 b001 null null
a001 b001 c001 null
a001 b001 c001 d001
a001 b001 c001 d002
-----------------------------

How can I treat a null column as part of the primary key? Is it possible to use a UserType to map database null to something not null in a java class to deal with it?

I don't have to deal with foreign keys now for these "primary keys".

Thanks.

Peiyun

You can't. The SQL standards say that primary key columns must be declared not-null, so hibernate's id tag has been designed with this in mind. You cannot model this table as a standalone entity. You can still refer to it via a collection, where the class is defined as a composite-element, but it can't have its own <class> mapping.