when would you use Session.load versus Session.get?

gigabee · **Joined:** Sun Jun 05, 2005 9:45 am **Posts:** 27

I just read the API documentation (I quoted it below) and I am curious when would you use Session.load over Session.get? When would you want a situation where hibernate returns a proxied object that represents nothing?

Quote:

Session.get:
Return the persistent instance of the given entity class with the given identifier, or null if there is no such persistent instance. (If the instance, or a proxy for the instance, is already associated with the session, return that instance or proxy.)

Quote:

Session.load:
Return the persistent instance of the given entity class with the given identifier, assuming that the instance exists.

You should not use this method to determine if an instance exists (use get() instead). Use this only to retrieve an instance that you assume exists, where non-existence would be an actual error.

Regards,

Joshua

christian · **Posted:** Wed Jan 04, 2006 9:13 pm

A proxy wraps an identifier. That is often all you need, an object that looks like the real thing, but didn't cost a database hit.

session.load(buyer);
item.setBuyer(b);

gigabee · **Joined:** Sun Jun 05, 2005 9:45 am **Posts:** 27

Christian,

I use Session.get to retrieve an object that does not exist, null is returned. If I use Session.load to retrieve the same object, I get back an object which throws an ObjectNotFoundException when I try to access any of its attributes.

When would you want an object back when you were not supposed to get one?

max · **Posted:** Thu Jan 05, 2006 9:56 am

to associate objects without unnecessary db access.

order.setCustomer(session.load(Customer.class, custid));

The customer object is never loaded from the database.

ekupcik · **Joined:** Sun Oct 09, 2005 6:36 am **Posts:** 19

You need to be a bit carefull when you are using inheritance though. Assume you have class A and the classes B and C which both extend A. When you use load(A, PKEY) you get a proxy that just implements A even if the object behind PKEY is a B or C as hibernate doesn't access the DB so it cannot know that the object is actually a B or C. When you call one of the mehtods that are defined in A the object itself knows that it is a B and works as expected. But you cannot cast the proxy you got from load() to B.

max · **Posted:** Thu Jan 05, 2006 11:43 am

yes - there is no free lunch, you need to know what you are doing ;)

snpesnpe · **Joined:** Sat Jun 12, 2004 4:49 pm **Posts:** 915

Quote:

to associate objects without unnecessary db access.

order.setCustomer(session.load(Customer.class, custid));

The customer object is never loaded from the database.

great naming - session.load(...) load never ...

david · **Posted:** Thu Jan 05, 2006 6:43 pm

Only when there is a class level proxy...

bchamp · **Posted:** Fri Mar 10, 2006 1:16 pm

Suppose you get a proxy via load(). Is there a cheap call you can make to check row existence before you proceed with calling methods on the proxy? Checking for null after a get() is pretty cheap, but does get() cost you that much more than load()? Will get() also return a proxy?