Hi,

In the system I am working on we use interface everywhere. Can anybody show me how to write the mapping file for interface? Here is an example



Another thing we have to do is we use one .hbm.xml per class.

Thanks.

A little bit more clarification of the problem in order to kick the tire here.

All the class mappings so far in Hibernate are based on concrete classes and interfaces are only for lazy loading rather than reference purpose I am using.

I am trying class/joined-subclass trick to make it more interface friendly (a good OO practice is acutally code on interface rather than class). Declare the class name as the interface class and declare the concrete implementation as joined-subclass.

But this will fail short for obvious reason I am specified in the question particular function call getFruit(). Everything else works perfectly.

Gavin & Co in the dev team:

Is it possible just adding one attribute in the class called interfacename, so that when I do "many-to-one" point to interfacename you know which class to go? It acts as alias to the class.


Maybe I overlooked whole a lot of issues here? Like how do you know which table to join if I ask getFruit(), right?

Thanks.

Why not use the <class..> <meta> attributes?

There is:
<meta attribute="interface">IFruit</meta>
<meta attribute="implements">IApple</meta>
<meta attribute="extends">Apple</meta>

Among other VERY useful attributes. I'm keen on using the "generated-class" attribute myself.

For more info, see section 18.2.2 on the Hibernate 2.1 beta(6?) or section 17.2.2 for the 2.0.3 stable release:
http://www.hibernate.org/hib_docs/refer ... guide-s2-2

Regards,
David

I think you need an <any> mapping here?

Actually to me it is a duh! I guess the document recommends not using it so I just skipped the entire Any session. After going back to read it, it made sense.

To me it seems that many-to-one can be completely replaced by <any>? <any> seems to map to type 'generic'/object which in java is a reference anyway.

Of course the downside of it is that you mix your column value with schema (I would rather column value be the concrete implemenation java class name than the table name though). Plus a little bit inconvience for the reader of the mapping file try to understand actually object type return, this force them to go to see the Java code, but I guess that's ok.

Thanks.

P.S. hidden in my mind, I still prefer a better way of handling code by contract(interface).

This is possible, just use:

Interesting, I skimmed through the code.

Meta-type has to be Type, CompositeUserType,UserType, serializable. I just tried Serializable (IFruit extends Serializable), it seems it serialize my entire class into table column which is not the one I want of course.

I looked at every other type of classes, all of them need to create instance. While in my case here is an interface as meta-type, so I guess it doesn't truely work, maybe I am totally wrong?

I don't know what you're talking about.

a meta-type is a Type that takes an instance of java.lang.Class and binds a column value. It does not take an instance of the associated class.

Why didn't you try my suggestion: meta-type="class".

I posted it for a reason....

Oh... Now I got it.

You meant literally 'class'. Well stupid me, trying to replace the 'class' with my interface class and it just throws me exception then I decided to figure why it throws me exception, then it leads my last post.

Now it works and CHARMINGLY, it indeed persist the class name in the db column.

Thanks Gavin for your valueable time.

Thanks for explaining the Any reference. I just tried it out and it's VERY interesting. Now, I'm more dangerous (Add manaical laughter here).

Regards,
David

Don't get too excited by any, guys ... navigating an any association in a query is problematic. You would need to use a theta-style join like:




I think its clear why this restriction exists ;)

David,

Consider <any> just likes setXXX(Object) and Object getXXX() + run time reflection (object.getClass() ). It lost the strong type support, and not quite good OOP (I meant pass every reference as Object type).

Gavin,

I think the query can be similar to many-to-one, and under-hood you can execute one extra select to get the many side of the table name from column value, then do a join right? So to me as a user, I still see I am in a clean query.

Guess a better interface based progamming support is still on my wish-list for hibernate (each time you see an interface, you will also attach a concrete class column beside it).

That would be VERY hard to implement :(