armtuk: Cheetah (Default)
2008-12-01 10:33 pm
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  • Current Mood: annoyed
  • Current Location: The Library
  • Current Music: Delerious - Glo
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Today's Hibernate Lesson

So for today's hard knocks hibernate lesson we learn that putting annotations on Member variables instead of Member Functions is a really bad idea. It breaks when you use inheritance. If you inherit from a MappedSuperclass and that superclass has members that are complex objects, then when you inherit them, all the annotations are ignored in the subclass, so you end up with database fields being of type bytea (at least in PostgreSQL) instead of being correctly mapped as foreign keys.

So in summary: Don't put annotations on member variables, always put them on member functions.

*SIGH* time to refactor 32 database classes.

At least I found the problem quickly.
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armtuk: Cheetah (Default)
2008-11-16 05:02 pm
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  • Current Mood: chipper
  • Current Location: The Library
  • Current Music: Crystal Method
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Hibernate Fun

I am struggling through Hibernate funness. I bought the O'Reilly book, but it's a bit thin, and after reading a few peoples' reviews, I also got the Persistence with Hibernate book from Manning which is AWESOME.

the merge method is evil. It looks like a good replacement for persist() but it isn't. merge() doesn't actually tie the object to the database state, so if you call merge() repeatedly on an object with no Id, it will save it repeatedly. persist() however does the right thing. The only thing merge gives you is the ability to save an object across sessions, but it would probably be better to attempt to re-attach the object instead of merging it.
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