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From "Clough, Samuel \(USPC.PRG.Atlanta\)" <Samuel_Clo...@princetonrg.com>
Subject RE: <typeAlias> support for C# Generics?
Date Thu, 31 May 2007 14:59:30 GMT
Since no one else has chimed in, I don't know if type alias supports
generics or not, I've never tried it.  It might be worth browsing the
code to see if it's immediately obvious if there's anything in there for
it.

  _____  

From: Tony Selke [mailto:tselke@liquidhub.com] 
Sent: Thursday, May 31, 2007 10:08 AM
To: user-cs@ibatis.apache.org
Subject: <typeAlias> support for C# Generics?



I have a problem that I either don't understand or which isn't currently
supported by the iBATIS DataMapper (v.1.6.1).  Any insight or
recommendations are greatly appreciated.

 

I use a heavily customized, generic BindingList as the collection for
all of my entity classes.  For reference, the type and its super-class
are shown below:

 

 

public class TList<T> : ListBase<T> where T : IEntity, new()

 

public abstract class ListBase<T> : 

   BindingList<T>, IBindingListView, IBindingList, 

   IList, ICloneable, IListSource, ITypedList, 

   IDisposable, IComponent, IRaiseItemChangedEvents, 

   IDeserializationCallback

 

 

If we use the traditional Northwind-based example, I have the following
sqlMap alias section in the config file associated with the Category
entity/table:

 

 

<sqlMap namespace="Northwind.Entities.Categories" . . . >

  <alias>

    <typeAlias alias="Instance" type="Northwind.Entities.Categories,
Northwind.Entities" />

    <typeAlias alias="List"
type="Northwind.Entities.TList&lt;Categories&gt;, Northwind.Entities" />

  </alias>

. . .

</sqlMap>

 

 

When I try to initialize the mapper instance like so: 

 

ISqlMapper map = Mapper.Instance();

 

I get the following inner exception:

 

"Could not load type from string value
'Northwind.Entities.TList<Categories>, Northwind.Entities'.":""

 

 

I am guessing that the issue has to do with how the SqlMapper is using
reflection to check/instantiate each typeAlias.  The reflection code for
dealing with generics is a bit more involved than a simple
Assembly.LoadFrom() and Assembly.CreateInstance().  More details with an
example can be seen here:

 

http://msdn2.microsoft.com/en-us/library/b8ytshk6.aspx

 

While I can probably get around this issue by having "collection
classes" that inherit from a typed-instance of my TList<T>, it sort of
defeats much of the purpose of the generic concept.  Is there something
I am missing?  Is there a way to do this without "hacking around" it?

 

Tony 
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