I need to sort the child object collection in a standard parent/child collection.

When I read a child object collection I cant use the "order-by" clause of the one-to-many bag because I am sorting by values retrieved elsewhere (through a many-to-one relationship from the child object). As far as I can tell, the "order-by" clause is passed straight thru to SQL and I can't put relationships, etc. in there.

So, I want to sort the collection after reading it. However, it is a lazy collection (IList) and doesn't support the Sort method. Also, the actual type is PersistentGenericBag, because it is a lazy NH collection.

What is the best way to sort these objects? Thanks

there are two methods that i know of; the first is using an HQL query to perform the order.


the second is to implement IComparable in the child entity class and use the System.Collections.ArrayList.Adapter(parent.CollectionOfChildren).Sort() method. not as effecient as sorting in SQL but will get you what you want.

Thanks for the reply. I didn't know about the Adapter.

I wonder if there is a generics version of the Adapter, since I actually have IList<Foo> and not IList. There doesn't seem to be a List<T>.Adapter. Oh well, I guess I can write my own easy enough...

Yeah, Adapter is good to know about. I would assume there would have to be a way to do it with generics. If there isn't, that seems like a somewhat major oversight. Microsoft seems to use interfaces a bit less than the Java folks do. What surprises me is that I would have expected a static Sort() method that takes an IList somewhere. Maybe there is one, but, I haven't found it yet. It seems like I've ran into other deficiencies with generics too although I can't think of anything offhand. My guess is that they'll proably polish up the generic collections in the next version of .NET.

Oh yeah, one other thing, that's been bothering me about .NET in comparison to Java is it's lack of a ListIterator class. This class in Java allows you to iterate over a list, and remove items while iterating over it.

It seems like there should be an easy way to create a List<T> from an ArrayList too. It's easy enough to just use a for loop to do it, but, it seems like there should be a method that does this for you.

Yeah, I ended up writing my own adapter. Kind of silly. The thing I am wondering about is if the list.Clear() and the list.Add() methods will confuse NH into thinking I am modifying the objects in this collection, but really I am just re-ordering them. Any thoughts?

In theory, I think what you're doing should work OK.

What I was thinking is maybe you could do is something like the following. However, in this case, I think it will screw things up because I think NHibernate may store other references to the collection. I could be wrong on that, but, I seem to recall having some issues when trying to do something like this way back when with the Java version of Hibernate.


Usually, I just initialize my collection once and don't change it after that.

I guess you could do something like this though.

Thanks for the information. It is indeed interesting if replacing the collection object would interefere with operation of NH. I'm guessing it works fine since once the collection has been initialized, NH no longer needs its proxied object?

I thought I read at some point that you weren't supposed to replace the collection or something, but, it may be the case that I'm just confused and misrembering. I guess the thing to do at this point would be just try it out and see if things go awry. That's usually the most authoritative way to figure things out. ;-)

you are right jemiller, you aren't really supposed to be replacing the entire collection. but i agree; generics are a new thing here and anything can be tried but for time and effort.

-devon

devonl,

That little bit about,
System.Collections.ArrayList.Adapter(parent.CollectionOfChildren).Sort() method

is precisely what I needed.

Nice, and thank you.