You can find all the juicey details here, but the short of it is that I've tested it and it worked. I have a working implementation which I could use to get smart generic collections for my business objects.
It's very cool, and it's amazing that ~400 lines of code took so much research. Oh well, I worked today to be lazy tomorrow :-)
I managed to build an addon to NHibernate that would allows you to use generic collections in NHibernate. Well, one collection, EntitySet<T>, but it's the principal that matter, and it's very easy to write additional classes to do the same for the other collections if you really wants it.
I used a custom PropertyAccessor, and I'm planning on releasing it tomorrow (once I wrote enough tests). But here is the client code that you'll have to write:
Post post = new Post();
blog.Posts.Add(post);
//Or you could do:
//post.Blog = blog;
//But you don’t have to do both
session.Save(post);
Here is how it looks like to the author of the classes:
public class Blog
{
...
EntitySet<Post> _posts;
public ICollection<Post> Posts
{
get { return _posts; }
}
public Blog()
{
_posts = new EntitySet<Post>(
delegate (Post p) { p.Blog = this; },
delegate (Post p) { p.Blog = null; }
);
}
...
}
public class Post
{
...
EntityRef<Blog> _blog;
public Blog Blog
{
get { return _blog.Value; }
set { _blog.Value = value; }
}
public Post()
{
_blog = new EntityRef<Blog>(
delegate(Blog b) { b.Posts.Add(this); }
delegate(Blog b) { b.Posts.Remove(this); }
);
}
...
}
This has a lot of goodies in it:
The guide lines for this are going to be:
My first attempt in using generic collections in NHibernate was to just make NHibernate grok my custom collection. I took a look in the code, and it seemed rather straightforward to do so. I posted to the developer list and got the following response from Sergey, the lead developer:
It's straightforward but a long process, and it involves some deep knowledge about the way NHibernate works. Luckily I managed to get it most of it pre-baked by transforming the existing Set collections to use generics. I started to run into problems when I had to dynamically construct generic types, but this article sums it pretty well. I could get the correct info and get it to work.
I decided to wait with that for now, and try a less invasive approach. I'm currently trying to get it to work using a Property Accessors. I'll post my results when I'm done.
I've been developing in .Net 2.0 [without ReSharper* :-( ], and I'm using NHiberante and Active Record for the data access layer. There were no problems with regard to their usage, but there are things that I don't like in the interface that they gives you. The problem is that you get an untyped collection. This was sort of OK in 1.0/1.1 but it's a really eye sore for developing in 2.0, where I want everything to be a generic type-safe collection.
Another issue with NHibernate is that the syncing between relationships is not automatic. That is to say, the following code is essentially a no-op:
Since the relationship is maintained on the other side of the connection. (Think about the way it's all laid out in the tables, and you'll understand why.) This is the bare minimum to get it to work:
Post post = new Post("Briliant Post By Ayende")
Blog blog = session.Load(typeof(Blog),1);
post.Blog = blog;
session.Save(post);
session.Flush();
But the above code has a serious shortcoming, it doesn't create the association in the blog, so you would need to re-load the blog from the database to get the change. This is undesirable, naturally, so you can do:
Post post = new Post("Briliant Post By Ayende")
Blog blog = session.Load(typeof(Blog),1);
post.Blog = blog;
blog.Posts.Add(post);
session.Save(post);
session.Flush();
Or create a method AddPost() that will do both operations in one line. This is something that bothers me, I like the natural way of doing blog.Posts.Add(post) to create associations. It's what a developer come to expect. The problem is that you can't add the code to do it to the Add() method on the list since the list is something that NHibernate supplies to you.
On the next installment I'll describe how I'm going to solve this problem.
* I did try, but it's not stable by far yet.
And 4 more posts are pending...
There are posts all the way to Feb 17, 2025
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