Hello,

I came upon an interesting problem:

I have a table,
which has an id and depends_on_id columns.
depends_on_id is constrained not to contain null values,
and I map a class SomeClass to it.

I use org.hibernate.id.enhanced.TableGenerator to generate the ids.

The caveat is that the value of depends_on_id depends on the id generated - that is I need to know the id before I can assign a value to the property mapped to some_column.

So, I tried the following code:

SomeClass obj = new SomeClass();
getCurrentSession().save(obj); // at this point the id is successfully generated
obj.generateValueForSomeColumn(); //using the id just generated
getCurrentSession().getTransaction().commit();

The commit (and not the save) fails with an exception which says that I've violated a not null constraint on depends_on_id.

If I remove the not null constraint - everything works fine.

My guess is that this happens since the commit does actually 2 operations like the following -
1. insert (id,null)
2. update (id,value)
And the insert fails, because of the constraint.


Am I right, and if so, how can I foretell the value of the id?

I can summarize the problem like this:

1. I need the generated id to create a value for depends_on_id column.
2. I cannot save the object to generate this id as I still don't have a value for depends_on_column, if would violate the not null constraint.

How can I possible break this magical cycle?

I will really appreciate any suggestions,
Vitaliy

save your object with a null ID and let the database create one for you.
example:

Once you've persisted your object you can call getId() if you really need t know what it is.

Hope that helps.

There is a not null constraint over the id column as well.

Thanks,
Vitaliy