Folks,

Is it possible to configure hibernate to return "empty" value instead of null for retrieval of component even if it is null in the persistence ?

<!--
example hbm file
-->
<class name="test" ...>
...
<component name="address" class="com.example.Address">
<property name = "line" type = "string"/>
<property name = "city" type = "string"/>
</component>
...
</class>

<!--
Expected value from retrieval for both line and city are null in the persistence
-->
empty com.example.Address (e.g. new Address())

Thanks in advance!

Chris

No, this is not possible.

It would be useful to have a way to express that we want the component object to be an empty object (new Address()) instead of null when all the component fields are null.

In my specific use case, I am using Spring MVC to bind form data values to the domain classes and I have something like



In my Company class, is specifically declare the Address member as



However since objects loaded from Hibernate set the address composite member to null, I end up getting NullPointerExceptions.

With hibernate setting the component member to null despite me having declared the address member as new Address() I now have an inconsistency introduced.

Using a user type for this is going to be complex as my current component has 'many-to-one' declarations which is nicely handled by hibernate when using a 'component'. Using a User type for handling a many-to-one mapping would require the UserType implrmentation to query the database and replicate logic that hibernate already handles.

Thanks,
Sanjiv

Perhaps you could handle this in your JavaBean instead. You could implement some logic in the set method that replaces the property with an "empty" object if Hibernate passes in null. Something along those lines.

Also, have you looked at CompositeUserType?

I had the same problem and I handled it in the JavaBean as rhasselbaum suggested: the set method replaces the null passed by Hibernate by an empty object.

One problem with this approach though: now Hibernate thinks the entity object is dirty, because null is not equal to the empty object I replaced it with in the setter. So the entity gets updated even if no changes are made. For this particular project this is a big problem, because the database tables are audited. Every update generates a new row in the corresponding history table.

This problem I solved by implementing a new CompositeUserType that considers null equal to an empty object. A much nicer approach would be to subclass ComponentType itself and overrule the isDirty method, but it does not seem possible to do that - how to make Hibernate use the new class?

Another feasable approach is to write an Interceptor that implements findDirty.

Excellent point. I had used rhasselbaum's suggestion too of setter replacing null with empty object. Will switch to using a custom CompositeUserType.

Thanks,
Sanjiv