Hi:

I have a base class called Person



It has a sub class called Manager



And my hibernate.xml is as follows:

<hibernate-mapping>
<class name="Person" table="Person">
<id name="ID" type="string">
<column name="ID" length="32"/>
<generator class="uuid.hex"/>
</id>
<property name="attr1" column="attr1" type="string"/>
<property name="attr2" column="attr2" type="string"/>
</class>
</hibernate-mapping>

I do not want to create a table for the subclass but want to store the subclass' (Manager's) data (only attr1 and attr2) in the superclass' (Person's) table.

So, I tried to run the following code,



But I get the following exception:

net.sf.hibernate.MappingException: No persister for: Manager
at net.sf.hibernate.impl.SessionFactoryImpl.getPersister(SessionFactoryImpl.java:344)
at net.sf.hibernate.impl.SessionImpl.getClassPersister(SessionImpl.java:2574)
at net.sf.hibernate.impl.SessionImpl.getPersister(SessionImpl.java:2581)
at net.sf.hibernate.impl.SessionImpl.saveWithGeneratedIdentifier(SessionImpl.java:725)
at net.sf.hibernate.impl.SessionImpl.save(SessionImpl.java:717)

Is what I am trying even feasible? If yes, please enlighten me.

Thank you,
Om

You don't have to map it to a seperate table, but you would need to map the Manager class.

Have a look at the docs regarding mapping inheritence hierarchies...

Om,

I am having the same problem like you and do not understand,
how I have to map the subclass.
Did you find a solution for this problem?


Thanks

You will need to add a discriminator and a subclass mapping to your person mapping, as follows:

<hibernate-mapping>
<class name="Person" table="Person" discriminator-value="Manager">
<id name="ID" type="string">
<column name="ID" length="32"/>
<generator class="uuid.hex"/>
</id>
<discriminator/>
<property name="attr1" column="attr1" type="string"/>
<property name="attr2" column="attr2" type="string"/>

<subclass name="Manager" discriminator-value="Manager">
<property name="attr3" column="attr3" type="string"/>
</subclass>

</class>
</hibernate-mapping>

You will also need to add a column called "class" to the Person table in your database. This is all described in the inheritance mapping section of the docs.

My subclass have no further fields which have to be stored in the database, only the fields of the base class are relevant for the persister.
Since there is an option for implicit or explicit polymorphism when loading objects from the database,
I think it would make sense to declare a subclass without a dricriminator when explicit polymorphism is used.

Or do I misunderstand something?

Hi,

Rather than start a new post on this already busy board I found this one that is very similar to my problem. We have a situation where we have a concrete class which is mapped in hibernate as Category. We're writing an application which will be extended by end users in creative ways. We would like the users to be able to subclass Category to add convenience methods (but not new persistent data). I'll call this subclass MyCategory.

Since the code containing the superclass is locked down and immutable for the end users, it's not really feasable to modify the hibernate mappings.

I see two problems here, 1 of which I have solved.

1) On retrieval of the object from the database, hibernate creates the object of the type given in the mapping file. Ok, I have an interceptor which overrides instantiate() to load a configured subclass instead and set the id. This works fine.

2) As discussed in this thread, hibernate needs to know about the persisteer to use and it doesn't know anything about MyCategory, only Category so it chokes saying
-- net.sf.hibernate.MappingException: No persister for: com.stormhq.util.hibernate.MyCategory

I have a couple of possible solutions that seem like they might work, but I'd rather not spend days trying to figure this out if it's already been solved.

1) Can one of the interceptor methods or a custom ClassPersister be used to provide the name of the super class to use as a persister?

2) Can a class be mapped as a subclass of a known hibernate object -- outside of the mapping of the superclass??? (This would be acceptable to us)

Any help would be greatly appreciated.

anyone has found a solution to this? i need it as well. basically the "Category" class is known to hiberenate. but the sub-class "MyCategory" doesn't contain any new persistent data. how can we make the load/save/find operations return MyCategory, not Category?

many thanks.