Hello,

I'm successfully using mappings which reference objects in different data stores / hibernate sessions. Per suggestions in the forum, I accomplished this using a UserType which knows which hibernate session to load a class from.

A problem occurs when using the UserType to load objects from multiple sessions in conjunction with caching. I'm hoping for feedback on:



Hibernate obviously handles this reloading automatically with a "real" many-to-one where the objects are in the same session. But, since I'm basically "recreating" a many-to-one using different hibernate sessions and a UserType, I need to manage this problem manually.



A possible addition to UserType to help with this problem: Have the option to have a UserType's nullSafeGet method called every single time an object is loaded whether from cache or database. Right now, it just calls it when loading it from the database. This would fix the problem because the UserType could "refresh" itself every time the object with the UserType gets loaded (whether from database or cache). I guess this is basically what I'm recreating in scenario #2 above only it would be more elegant to handle this in the UserType itself.

In short, hibernate only seems to call the UserType when loading from the database. It would be nice if there was an option to have it call the UserType when loading an object from the cache as well.

Any and all suggestions are welcome. :) Please let me know if I can elaborate! It seems like objects with references to objects in other sessions should be elegantly handled via UserTypes. But, scenario #2 doesn't seem all that elegant.

Thanks,

Ryan

Another thought. Instead of using a <property> and a UserType for these objects which come out of other sessions, what if the actual <many-to-one> element was used for these objects. Is there some way to interecept the loading of a many-to-one object and have it use a different session to load itself? Then I wouldn't even need a UserType at all.

Going back to the example, object #1 would have a many-to-one mapping to object #2. Everytime object #1 was loaded from database or cache, it would try to reload object #2. I believe it does this now even when they are in the same session. Is there some way to force object #2 to load from a different session than object #1?

Ryan

Unfortunately, UserType does not allow you to overload assemble/disassemble. However, CompositeUserType does. So perhaps you could use a CompositeUerType.

I love hibernate! Upon initial testing, the CompositeUserType seems to have solved the problem of "objects across multiple data sources" beautifully!

Thank you,

Ryan

Cool. Hey, it might be nice if you could write something about your solution on the "design patterns" section of the Wiki. Other people are also doing this kind of thing....