Hoping for a bit of design help here. This is what I have:

class File; // info about a file, including its location on disk

class ImageFile extends File; // adds info on format, size etc

some memory holding the contents of a nameless file.

This is what I want to do

1) Construct a File and persist it in order to get a unique ID
2) Write out a corresponding on file on disk with the database ID in its name, dumping the contents from memory
3) Check whether the file is a recognized image format (using external program -- this is why it needs to be dumped to disk first)
4) Re-set Hibernate/DB entry to ImageFile type if necessary

My question is, is this possible to do safely in Hibernate, using joined-subclass or discriminators?

I can think of various workarounds involving either

1) writing out a temp file, testing it, constructing a File or ImageFile as appropriate, persisting it, and renaming the file, or
2) not using inheritance, rather just have a possibly null field in File pointing to another entity with image related info (a kind of faked joined-subclass)

but both of these are rather clumsy. I'm hoping some more experienced Hibernate users can help me with something more elegant.

thanks

This is the same problem as "can my object change its Class Type during its lifetime", which is not possible of course. This has been extensively discussed in the forum already in an older thread. I'd suggest you redesing your class model.

Great, thanks for the quick reply. I'll try searching again.

This definitly should be supported. Of course, only for changing types walking up and down in the same hierachy....