dynamic mapping of table columns to different objects

bhumit · **Joined:** Mon May 01, 2006 11:14 am **Posts:** 1

Hi

My requirement is like this: I have a table A. Depending on value of A.col1 I want to map other columns of this table to other objects.
For example, If col1 has value 2, I want to have primary key of another table B(object B) into my A.col2 i.e. I want the object B to be part of Object A via column A.col2
If col1 hsa value 3, I want to have primary key of another table (object) into my A.col3

P.S : I already have values in column A.col1. I couldn't find any use of discriminator in this case.

Any suggestions would be appreciated.

Thanks
Bhumit

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

My preference for this situation is to use separate classes and separate mappings. Use the where="" attribute of the class element. Something like this:

Code:

<class name="TableAClass1" where="col1=1">
  ...
  <property name="Col1INTERNAL" column="col1"/>
  <many-to-one name="Foo" column="col2"/>
  ...
</class>

<class name="TableAClass2" where="col1=2">
  ...
  <property name="Col1INTERNAL" column="col1"/>
  <many-to-one name="Bar" column="col2">
  ...
</class>

Note that, in order to insert new rows to table A when using this method, you need to have somewhere to store the "discriminator" value (the one in the where="??" attribute). Make this a member of the class, but have the set method do nothing, and the get method returns the "discriminator" value. This makes hibernate think that it's just another value that it needs to write to the table, but doesn't expose it to the users.

There are other ways of doing this. I've never investigated them though, because this way is easy, and the overhead is tiny: just two stub methods.