Hello,

here's my problem :

I have a MappedSuperClass A, with two Entity subclasses B and C, mapped on separate tables.
A declares a foreign key property, say 'children', which is properly implemented in B.
But C, for usecase specific and performance reasons, never has children, and should not have it in its db mapping :



Now, I want to express a query (in my case in HQL), where I say :



And this fails, since C does not have any DB mapping for 'children' :
org.hibernate.QueryException: could not resolve property: children

How can I implement this ?
Is there any way to override a property and mark it as being a constant or null in one of the subclasses, so the mapping doesn't try to resolve it ?
Or do you think there's a flaw in my object model design if I need to do that ?

thank you

Have you looked through the Inheritance Mapping docs?

http://www.hibernate.org/hib_docs/refer ... leperclass

I'm not sure but implicit polymorphism may do what you need.

Yes, I have gone through the inheritance mapping docs. I've read about implicit polymorphism, but I didn't feel it would solve my problem.

What I would really like, is make Hibernate understand that, for class C, there are never children, and there should not be any column for the foreign key.
Just as it is possible to override an attribute and map it on a different column, i'd like to override the attribute by mapping it on NULL, or no column, whatever you call it.

Or did I miss something about implicit polymorphism ?

I think I'm still confused or something I'm still missing here.

How are your mapping files structured? Is it not possible to move the mapping of children into B's mapping instead of A's?

yes, i can move the mapping down in B, but my problem still remains : I need to express a query on A (i.e. B and C together), where the children property is at stake, but that property is not mapped in C.

Let me give another example :



where 'name' is a property defined and mapped in A.

this should match B instances that have a 'foo' child, and all A instances (B and C) that have 'bar' as name.

To achieve this, Hibernate must understand that, when resolving the 'children' property, it must ignore C, and only query for B.

thanks

Ah, I understand.
Unfortunately I can't give you any suggestions :(

The problem is that your query does not correspond to your mappings. Since you want to write a query on A, the children property needs to be on A also; otherwise you are asking for something that doesn't exist. If you cannot have the children property on A but must be on B, the query needs to be written against B. If you need the results from C also, use a union or a second select; of course that is not possible if your query does a join between B and C.

The problem is that your query does not correspond to your mappings. Since you want to write a query on A, the children property needs to be on A also; otherwise you are asking for something that doesn't exist. If you cannot have the children property on A but must be on B, the query needs to be written against B. If you need the results from C also, use a union or a second select; of course that is not possible if your query does a join between B and C.

The problem is that your query does not correspond to your mappings. Since you want to write a query on A, the children property needs to be on A also; otherwise you are asking for something that doesn't exist. If the children property must be on B, the query needs to be written against B. If you need the results from C also, use a union or a second select; of course that is not possible if your query does a join between B and C.

Sorry for the multiple posts, the web site is so unresponsive that you don't know if and when something got through.

that's the answer i hoped not to get, I have to say...

It thought it should be possible, because you can, for instance, define a mapping in A, and then override it in B and C, with different columns for each.
In that case, hibernate will handle it nicely, and do the query on the appropriate column for each subclass B and C .

From there, i thought it should be possible to override the mapping to target no column, which is just a special case.

anyway, thanks for the answer.