Difference between implicit and explict polymorphism

etwcn · **Joined:** Thu Feb 08, 2007 10:40 am **Posts:** 46

Hi!

Where can I find documentation about the difference between implicit and explict polymorphism?

I already checked this link, but it does not help.

thanks for help...
etwcn

scesbron · **Joined:** Thu Sep 04, 2003 8:23 am **Posts:** 368

What do you want to know exactly ?
Your link point to the right place in the documentation, theres is also a table at the end to summarize the main differences

etwcn · **Joined:** Thu Feb 08, 2007 10:40 am **Posts:** 46

I will try to give an example. Imagine I have table-per-hierachy mapping strategy for vehicle-hierachy:

Code:

<class 
   table="Vehicle" 
   polymorphism="explicit"   <===============
   name="Vehicle">

   <subclass
      name="Bus" discriminator-value="bus">
   </subclass>

   <subclass
      name="Truck" discriminator-value="truck">
   </subclass>

    ...
    ...

</class>

Now... where is the difference between writing polymorphism="explicit" and polymorphism="implicit" at this mapping?? I tried both - it does not seem to make any difference.

etwcn

etwcn · **Joined:** Thu Feb 08, 2007 10:40 am **Posts:** 46

scesbron · **Joined:** Thu Sep 04, 2003 8:23 am **Posts:** 368

Quote:

Implicit polymorphism means that instances of the class will be returned by a query that names any superclass or implemented interface or the class and that instances of any subclass of the class will be returned by a query that names the class itself. Explicit polymorphism means that class instances will be returned only by queries that explicitly name that class and that queries that name the class will return only instances of subclasses mapped inside this <class> declaration as a <subclass> or <joined-subclass>. For most purposes the default, polymorphism="implicit", is appropriate. Explicit polymorphism is useful when two different classes are mapped to the same table (this allows a "lightweight" class that contains a subset of the table columns).

cf http://www.hibernate.org/hib_docs/v3/re ... pping.html