I'm trying to use NHibernate to persist my clases to the database. In

order to do that, all "set"s must be mapped through a Iesi

collection, so all of my collections are declared as

Iesi.Collections.ISet. i.e.:



As it's going to be a web site that uses this clases, I wanted to

serve them as web services, using an SOA architecture. I tested the

NHibernate mapping files and everything with a windows form, and it

worked fine, so I created the web service that would serve my website

(and any website that might want to use it) and added a getCountry

web method. To my surprise, when I tryed to test it, I found out that

, despite the project compiled perfectly, I got an error message

saying: "You must implement a default accessor on Iesi.Collections.ISet because it inherits from ICollection.". I did some research, and found out that the interface Iesi.Collections.ISet cannot be serialized, and that's what causes the error... Unfortunately, I also noticed that everybody allways used some workaround to solve this problem, but it's allways a patch and never a solution... so, my question is, did I make a mistake choosing NHibernate? Applications are more and more using web services to interact with other applications, so is the NHibernate team (or the Iesi team) going to solve this problem? Is there an easy solution to be able to use web services that doesn't include "cheating" nor hours of refactoring?

Alex.

You should create some test cases using plain objects to see what can be sent over trought web servciers and what can not. AFAIK, big interrelated object graphs (with back-links) are always quite a big challange for a web service. All this is not related to NHibernate but a basic structure how SOAP messages are formed.

Anyway, I have seen no solution of sending data over web services so that it would not require cheating nor hours of refactoring. If You find some, let me know - I would be glad to hear. And we might be able to figure out how to make it doable with NHibernate.

Gert

I agree completely with Gert.
At this point I do it myself: serializing to normal arraylists. (or generic lists).

I would very much like for the nhibernate team to give more hooks in the nh-collections. When returning from the client with data to be saved/inserted/deleted, I wish I could create the bag myself.

The error is thrown only if I have a property of type Iesi.Collections.ISet . If I remove or hide this property, I don't get the "You must implement a default accessor on Iesi.Collections.ISet because it inherits from ICollection." error. So I changed my "Country" class so it looks like this (I saw it somewhere else in the forum):



which ignores this property when serializing, so it doesn't raise the error. Then I added



This "overrides" the States property, and returns an ArrayList, which is serializable. So this works, and does not raise an exception. Buuuut (there's always a but) it does raise a mapping exception. My mind is melting at this point...

If StatesList is not mapped, why should it raise mapping exception? Knowing exception details might be helpful.

Two things to note. First, you should declare your collections as generic ICollection objects. If NHibernate uses a different collections library in a future release you would have to search and replace all the code that declares your collections as Iesi.ISet.

Second, just because you are developing a web site does not predicate the use of web services. You can use NHibernate objects directly from within your web app. Web Services should be reserved (in my humble opinion) for external and cross platform communications(i.e. Java - .Net and even then there are better alternatives). I'd definitely steer clear of webservices if you ever intend to use generics in your software. They are not supported...period.