I have a xml file with data from various sources. For example:

<root>
  <Account>
    <Id>1</Id>
    <Name>Somename</Name>
    <City>Somecity</City>
    <ContactPersons>
      <ContactPerson>
        <Id>1</Id>
        <Name>Somename</Name>
      </ContactPerson>
      <ContactPerson>
        <Id>2</Id>
        <Name>Somename2</Name>
      </ContactPerson>
    </ContactPersons>
  </Account>
</root>

I created a generic businesscollection (named BusinessCollection) and a business class (named BusinessObject).
Then I created a specific business class named Account en another one called ContactPerson. They both derive from the BusinessObject class.

I created a instance of a businesscollection with accounts using:
BusinessCollection <Account> collection = new BusinessCollection <Account>();

I also made a parser that 'translates' the xml into the correct business classes. So in case of the data above I
provide a instance of BusinessCollection <Account>. Then I create Account objects and add them to the collection. This is all done
using reflection and some XPath classes.

The parser has the folling method signature:
public static void ParseToBusinessObjects <T>(BusinessCollection <T> collection, XPathDocument document) where T : BusinessObject

So far so good. But now I also want subcollections to parse. In the xml data ContactPersons will be my subcollection (property is named the same).
If my parser detects a subcollection it will get the current instance (using reflection). I then want to call my entry method again for this collection (recursive)

However when I do this:
BusinessCollection <BusinessObject> subCollection = (BusinessCollection <BusinessObject>) property.GetValue(instance, null);

I get a InvalidCastException saying I can't convert between a BusinessCollection<ContactPerson> and a BusinessCollection<BusinessObject>.

Its the same when I change it to :
BusinessCollection <T> subCollection = (BusinessCollection <T>) property.GetValue(instance, null);

I hope someone knows how to solve this because its driving me nuts.

So far I envision your code looking like this. If not, please post a skeleton of your code.

using System;
using System.Xml.XPath;

public abstract class BusinessObject { }
public class BusinessCollection<T> where T : BusinessObject { }
public class Account : BusinessObject { }
public class ContactPerson : BusinessObject { }

public class Parser
{
   public static void ParseToBusinessObjects<T>(BusinessCollection<T> collection, XPathDocument document) where T : BusinessObject { }
}

Could you post your code that relates to this line:

BusinessCollection <BusinessObject> subCollection = (BusinessCollection <BusinessObject>) property.GetValue(instance, null);

HTH,
Ryan

Thats about right but I already got the answer I was looking for aldough its not what I hoped for. Its not possible yet because generics don't support covariance.

Only doable using interfaces and in my case thats no an option because of various reasons.

I solved it by creating an internal class method which expects an object instead of a BusinessCollection<T>. I then call the add(obj): method on the collection using reflection:

MethodInfo info = collection.GetType().GetMethod("Add");
object[] paramaters = new object[1];
paramaters[0] = businessObject;

info.Invoke(collection, paramaters);

Its not a very clean solution but it works for now.

Thnx!

Doormalena, I have been going nuts with this too for almost a week now. I can't believe you can't cast one list to it's base but I believe you've got a work around. I can't use that for my purposes but would like to know what forums you've researched so I can look at as well.

 

THanks,

Santiago

this may help you

http://www.cisco-cert.com/Addison%20Wesley/C.Sharp.Programming.Language

saintperez:

Doormalena, I have been going nuts with this too for almost a week now. I can't believe you can't cast one list to it's base but I believe you've got a work around. I can't use that for my purposes but would like to know what forums you've researched so I can look at as well.

 

THanks,

Santiago

Sorry for the late response. Didn't monitor this thread anymore. I used the c# news groups allot because I got more replies over there.

I btw now changed the above solution to pass on a generic list interface (IList<T>) instead of a custom collection. The list has already a Add method.