Uli,
Using Object for key fields is a standard micro pattern in JPA and
Hibernate. Of course, the DB does not want to save null as a key field
value, but the most people get the entity manager to auto-generate keys
for their objects.
By leaving the key as null, the entity manager knows that it needs to
persist the object, generating a key for it. This is a handy pattern,
when you want to create a parent object with several children, and then
persist the whole object tree in one call (otherwise, you would have to
persist the tree, one object at a time, from the bottom up - Yikes!).
JPA/Hibernate can only do this if it knows what a null key value is, and
in Java that is of course, null. I think (from memory) you can define a
specific value as a null, so you could use an int or a long as a key
field type, and then specify, for example, -999, as the null value.
Then, you have to set the key field to -999 somewhere, and this is all
too much work for most people, therefore, they use Object key field values!
Ciao,
Jonathan
On 10/02/2009 08:08, Ulrich Stärk wrote:
Thiago H. de Paula Figueiredo schrieb:
Em Mon, 09 Feb 2009 22:35:52 -0300, Luther Baker
<lutherba...@gmail.com> escreveu:
Simply stated, I'm asking about the two orthogonal choices: (native vs
object, range or size)
Is an int preferred to an Integer? Is there a compelling argument
for either native or Object?
I guess that you mean "primite" when you mean "native".
Native types in Java can't have null values, so, for primary key
properties, a Integer is a much better fit than an int.
Why is that? I couldn't imagine a case where you want your primary key
value to be NULL (apart from the fact that I don't know any DBMS that
allows that).
Uli
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