outer-join setting and proxy class

nodje · **Posted:** Mon Mar 22, 2004 10:58 am

Hi everyone,

sorry for the stupid question, but i need to be sure:

Does it makes any sense to insert a outer-join="true" if the associated class HAS a proxy??

Or is Hibernate going to eager fetch this proxied class and instanciate it each time? and even in this case, it might be usefull for the class to be lazy instanciated for any other use of it.

christian · **Posted:** Mon Mar 22, 2004 12:14 pm

If you have A many-to-one-with-outer-join-true B (proxy), Hibernate will load both instances of A and B if you load A, with a single outer join select. The proxy setting is not relevant.

If you have A many-to-one-with-outer-join-false (proxy), Hibernate will only load A and use a proxy for B. A second select will be used to fetch B on demand.

If you have A many-to-one-with-outer-join-true (no proxy), Hibernate will load both instance of A and B if you load A, with a single outer join select.

If you have A many-to-one-with-outer-join-false (noproxy), Hibernate will use two selects to fetch A and B when A is loaded.

Please note that for one-to-one and many-to-one associations, outer-join fetching is usually enabled by default (auto). You can control this behavior with the max_fetch_depth Hibernate property (0 turns it off).

anthony · **Posted:** Mon Mar 22, 2004 12:44 pm

Christian,
i've seen this kind of question many times.

Quote:

If you have A many-to-one-with-outer-join-false (proxy), Hibernate will only load A and use a proxy for B. A second select will be used to fetch B on demand.

It is easy to code such a proxy?

Thanks,
Anthony

christian · **Posted:** Mon Mar 22, 2004 12:46 pm

Set <class lazy="true"> and have a no-arg constructor with package visibility. Thats all.

anthony · **Posted:** Mon Mar 22, 2004 12:58 pm

that's all?
great, thanks a lot!
Last question, what will happen if <class lazy="false"> ..., i mean is it supported for the previous versions (especially 2.0)

Anthony

christian · **Posted:** Mon Mar 22, 2004 1:07 pm

Please read the documentation, "Performance" chapter. Setting lazy=false disables proxying for this class.

anthony · **Posted:** Mon Mar 22, 2004 1:15 pm

oh, excuse me, in fact the question was: for previous versions, the lazy attribute is not available (for a class) so for previous versions it will work as if lazy="true" ?
But no problem, i will download previous docs tomorrow and test it.

Anyway, thank you.

Anthony

christian · **Posted:** Mon Mar 22, 2004 1:20 pm

lazy="true" is in that case just a shortcut for proxy="theNameOftheProxyClassIsTheSameAsTheBaseClass"

anthony · **Posted:** Mon Mar 22, 2004 2:34 pm

ok, thanks again Christian

alistair · **Posted:** Mon Mar 22, 2004 10:48 pm

Christian,

[quote]Set <class lazy="true"> and have a no-arg constructor with package visibility. Thats all.[/quote

I had a read of the chapter on performance but it doesn't really say what's needed in the proxy class specified in the proxy attribute. <class name="foo" proxy="myProxy"> What i've done is just extract an interface from my persistent class (Eclipse makes this easy) and plonk that in. I hope I'm doing the right thing.

Regards,

Alistair

alistair · **Posted:** Mon Mar 22, 2004 11:16 pm

OK. After testing this, it works fine to just name your persistent class itself in the proxy attribute. CGLIB performs magic behind the scenes. It's working.

alistair · **Posted:** Tue Mar 23, 2004 3:49 am

However, ... I have one more question.

Code:

   /**
    * @hibernate.many-to-one
    *      column = "orig_id" 
    *      class = "Foo" 
    *      unique = "true"
    *      cascade = "none"
    */
   public FooProxy getFoo() {
      return foo;
   }

My property is now set to be of type FooProxy, an interface. Should I change my relationship in the mapping file to point to the original class, Foo or the FooProxy ?

Regards,

Alistair

christian · **Posted:** Tue Mar 23, 2004 5:49 am

You should not do anything special :) Set lazy="true" for your class and have a package visible no-arg constructor. Hibernate will do the rest.