Hey guys,

I am trying to query for a class that is made up of a composite primary key using the session.get(Class, Serializable) method. Pseudocode:

ie.

test.hbm.xml
<composite-key>
<key fname>
<key lname>
</composite-key>


want to

session.get(test.class, ????);

what should go in the question marks???

thanks in advance.

You need to give it the key object. If you've mapped properties of your entity as the key then your entity is also the key.
e.g.
Say User is your mapped object with properties fname and lname as the key. To load a user by pk you need to do this:


You should avoid composite Ids unless mapping to a legacy schema.

thank you. So when dealing with hibernate columns that define the table should not be a composite key? That kind of goes against ER database, correct?

Ie. I have a table where the three columns define its primary key, how should I change this to be hibernate complian then? create a unique_id and disregard the other three columns as beinga composite?

If I choose this solution I the .saveOrUpdate() will not function properly because the primary key is not defined properly? Could you possibly clarify this?

Hibernate _can_ use composite keys its just the hibernate people think they are a bad idea. In the docs it says this for example:


It certainly complicates your mappings and has some undesirable side effects, like the issuing of a select before an insert to determine if an object should be inserted or updated.

You should use a simple surrogate primary key like a Long for example, and map the other fields as properties. If you have data that should be unique you can still define a unique constraint across these fields to ensure data integrity. And of course, you can always query for instances using the fields that would have been in your composite pk.

saveOrUpdate works perfectly well with a surrogate key.