Hibernate version:1.0.2

I'm new to nhibernate (and c#), but am ploughing through. I could do with some advice regarding xml serialization and nhibernate.

I want to be able to take a xml document and deserialise it into a set of objects and then persist these with nhibernate. however, if the root object already exists (ie a key value is the same) i want to update this object (and it's children) rather than just adding a new set of objects.

what's the best way to do this? is there a way? or am i barking up the wrong tree completely.

thanks,
mike.

i was reading this over the weekend:

http://www.hibernate.org/368.html

haven't tried it yet, though.

-devon

hmm, looks interesting (and complicated!). if i read it right though, i think this solution is to create an xml property type rather than deserialising from xml to .net objects and then nhibernating them. i shall go through it in some more detail...

mike.

actually, it doesn't look too complicated. one caveat is that all properties rturn the type XmlData and we know that sometimes we want an "int" or a "bool" or a "string" and so there must be some mechanism to cast these without having to cast a property every time you use it. or maybe i'm missing something...

-devon

I haven't tried using XmlSerializer directly, but, in theory it should work just liked it does with ASP.NET XML web services which uses XmlSerializer for serializing/deserializing data.

Basically, "it just works". You just call ISession.SaveOrUpdate() and pass it the object graph that you want to save to the database. NHibernate checks the key value for the object(s). If it's not set to the "unsaved value," then, it does an UPDATE, otherwise it does an INSERT.

One potential problem you might run into though is that XmlSerializer doesn't handle circular references (as far as I know). If you have bidirectional relationships between objects you will.

BinaryFormatter and SoapFormatter are supposed to be able to handle circular references. SoapFormatter has the disadvantage that it doesn't handle generics (as far as I know).

Also, if you're using ASP.NET web services, you can used RPC encoding instead of the default if you need circular reference support. However, this is possibly at the cost of compatibility. Not sure what ASP.NET is doing under the covers to acheive this.

this is true. in this instance, if you didn't want to use the binary formatter, you use the XmlInclude attribute to include a reference to the object contained within the collection. kind of a hack because you end up with all kinds of XmlInclude references (you have to hit all objects in the graph even if they're four levels deep).

ok, so i receive and deserialise the xml. I have a reference, but it is not the actual id field (this is internal to nhibernate and i don't want to pass it around0. however, i can get the object using reference and this gives me the id. i then put this in the object and it's child objects and then isession.saveorupdate. it seems a bit messy, but it should work?

mike.

I'm not sure I understand you. If what you're saying is that you don't want the id values being XML serialized, then, I don't think that will work. NHibernate needs the id values in order to know which object is which and whether it's a new object that should be "saved" or an existing object that should be "updated" (based on whether the id value is set to the "unsaved value" which is normally null or 0 assuming you're using an auto-increment id).