Hi,

my problem is that I do not how/where to start with hibernate
and the following setup:

We have a mysql legacy database. In it there are some tables
that have a composite key.

for instance:

myID : unsigned integer, not null, auto_increment
appoved: boolean, not null
data: varchar(200)
someMoreData: varchar(100)
...

the primary key is actually (myID, approved).

The setup is a follows:
data is submitted or updated and comes in a approved=false state
record. All the while the data in the approved=true record (on an
update) is still the same.

Then another user reviews the data and approves it, upon which
the object is again persisted into the approved=false state and
also updated (or inserted) in the approved=true record.

My question is actually:
how to map such a construction? Are there some interfaces to
implement on the pojo's? specific classes? methods?

And for the persisting ... how to do it easily if it can be done at all?

It is a demand that at any one time, there is only 0,1,2 records
with a certain myID inside the table.

kind regards,
Dimitri Smits
aka gongo

There are several ways that will work. The first doesn't really address your question but might be a better solution: add a new column for the primary key and convert the existing PK into a unique key. That's what I'd do in this case as it's generally better to keep business meaning out of the PKs.

The other 2 approaches are:
1. Use a <composite-id> for this mapping. Easy to do, see the ref docs. Note you MUST implement equals() and hashCode() for your composite ID class (jakarta commons lang Builder classes make this easy).

2. If you don't need to access these on their own, but rather they are always accessed via some other object (e.g, the child side of a parent-child relationship), then you can use a component mapping. Dependent components have a compound pk of their <key> and <index> columns.