Hello,

I would like to know if there is any possibility to change the polymorphic behaviour of queries at runtime. To be more explicit, can I specify on a query that it has explicit or implicit polymorphism ? If it is not possible, how could I at some moment load only the properties of a root class (and instantiate this class), with implicit polymorphism set in the xml mapping file ?
I use a table per joined subclass strategy.

Thanks,
Florin Cremenescu

Hibernate has to do the join to know the concrete implementation of your class to be consistent with the OO aproach, so loading the proerties will not make much difference.
If you want to lazy load a part of your propertires, consider mapping you joined-subclass into a one-to-one

Hello,

I don't see the point. I think I don't understand well the difference between the implicit and the explicit polymorphism. I thought that by mapping a class with explicit polymorphism, a query using the name of that class will return instances of that class only, and not of its subclasses or joined-subclasses. If this is true, I don't understand your consistency concern with the OO aproach. And, again if this is true, why is it possible by specifying "explicit polymorphism" in the xml mapping file ?

Your solution consist in replacing all joined subclasses with one-to-one mappings ? It is not realistic, because a class could have several subclasses.

Loading only the super class part of a mapping is only a problem of performances, and I think that Hibernate should offer this possibility (by explicitly specifying it in a query), even if this breaks some OO.

Thanks for your help.

Florin Cremenescu

Explicit polymorphism DOES NOT disable "mapped" polymorphism, expressed via <subclass>, <joined-subclass> or <union-subclass> mappings!

I begin to get the point. But there is no possibility to load only the super class part of a class (beyond the HQL specifying all the properties of the super class) ?

Thanks,
Florin

I was wondering if someone has an anwser to Florin's last question.

Hi, I think this functionality would be very helpful. You can for example use "index-only" database fetching which is greatly faster than accessing database table by row id.

Is it possible to off polimorphism at all ? I don't need it everytime, moreover sometimes it's very inconvienient.

Can't hibernate make an exception when using a discriminator ? Because the discriminator ALREADY tells Hibernate what subclass to instantiate without having to hit the table mapped to the subclass.

Thus, the behaviour that I was hoping for is that:

1) Hibernate checks the value of the discriminator column / formula, then creates an instance of the subclass as defined by the discriminator value ... BUT ... without loading the properties of the subclass. That is, it does not do a SELECT on the table mapped to the subclass.

2) When a get/set property of the subclass is then called, THEN Hibernate will do a SELECT on the table mapped to the subclass.

Reason for this is that, there are quite a few cases where we want the return a large list of entities from the parent class ... and we are not expecting to use any of the properties of the subclass, but there are some cases where we do.