Is it possible to do lazy-loading of many-to-one children (ie. children that are not collections) with NHibernate? I've done a search on this and couldn't find anything, but I'm sure someone must have posted about this before.

Obviously it would require me to modify the code in my class, but that should be fairly simple and I think it could be quite helpful. Something like this:



Of course, it gets more tricky if the child is optional (ie. null is a valid value).

lazy loading is the default in hibernate. if you don't change anything by yourself your LazyChild object should actually not be loaded.
you should not place any data access logic in your domain object! just let it as a "normal" property:

and on an other place you can check if it was already loaded:

for more informations about lazy loading please see the NHibernate documentation.

greez simon[/code]

I found the part about proxies in chapter 14.2 of the manual and that's what NHibernateUtil.Initialize() seems to be for, but it's not really what I'm after. I want the lazy-loading to work with polymorphic classes and don't want to make everything virtual. Can't all that be avoided by simply adding some code around the field access that checks whether the field is initialized?

do i understand you right that you like to inherit from your Parent class and override the property with a different return type? you could maybe define an Interface for that return type. maybe section 8.1 in the documentation can help you.

Sure, I could do that sort of thing, but I don't want to significantly change my code to work with NHibernate. It's NHibernate that should work with my code. So adding some extra code to a property getter is fine, because it's encapsulated and doesn't affect anything else, but defining interfaces, sacrificing polymorphism, making everything virtual, etc. is too much.

well, of course can you do that (even if i don't think that it is a good practice). you just have to map the id attribute of the LazyChild in the Parent class. additionally your Parent class needs an instance of the hibernate session. the rest is exactly as in your example from the first posting.

Yes, that should work, but then I'm basically losing the benefits of NHibernate like being able to save the child together with the parent (if it's dirty).

if you like to save the child together with the parent (with the cascade option), then you have to map the LazyChild property and then it has to be virtual! so you have to decide, map with hibernate or implement your own lazy loading...!
by the way, you can save your child by your self, just implement the ILifecycle interface in your Parenc class and save the child right before the parent is saved.