I’m relatively new to NHibernate, but have been using it for the last few programs and I’m in love. I’ve come to a situation where I need to aggregate data from 4-5 databases into a single database. Specifically it is serial number data. Each database will have its own mapping file, but ultimately the entities all share the same basic structure (Serial class).
I understand NHibernate wants a mapping per class, and so my initial thought was to have a base Serial Class and then inherit from it for each different database and create a unique mapping file (the inherited class would have zero content). This should work great for grabbing all the data and populating the objects. What I would then like to do is save these inherited classes (not sure what the proper term is) to the base class table using the base class mapping.
The problem is I have no idea how to force NHIbernate to use a specific mapping file for an object. Casting the inherited class to the base class does nothing when using ‘session.save()’ (it complains of no mapping).
Is there a way to explicitly specify which mapping to use? Or is there just some OOP principal I am missing to more specifically cast an inherited class to base class? Or is this idea just a bad one.
All of the inheritance stuff I could find with regards to NHibernate (Chapter 8) doesn’t seem to be totally applicable to this function, but I could be wrong (the table-per-concrete-class looks maybe useful, but I can’t wrap my head around it totally with regards to how NHibernate figures out what to do).
I don’t know if this’ll help, but I wouldn’t be trying to do that, basically.
Essentially, I think you’re possibly suffering from ‘golder hammer’ syndrome: when you have a REALLY REALLY nice hammer (i.e. Hibernate (and I share your opinion on it; it’s a MAGNIFICENT tool)), everything looks like a nail.
I’d generally try to simply have a ‘manual conversion’ class, i.e. one which has constructors which take the hibernate classes for your individual Serial Classes and which simply copies the data over to its own specific format; then Hibernate can simply serialize it to the (single) database using its own mapping.
Effectively, the reason why I think this is a better solution is that what you’re effectively trying to do is have asymmetric serialization in your class; i.e. read from one database in your derived class, write to another database in your base class. Nothing too horrible about that, really, except that it’s fundamentally a unidirectional process; if you really want conversion from one database to the other, simply do the conversion, and be over with it.