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From "EXT / ASTEK MOUSSON Nicolas" <ext.astek.mous...@sncf.fr>
Subject RE : <typeAlias> support for C# Generics?
Date Thu, 31 May 2007 15:19:00 GMT
 

To use your generic class with iBATIS, just use the following syntax in your alias:

 

  <alias>

    <typeAlias alias="List" type="Northwind.Entities.TList`1[Northwind.Entities.Categories],
Northwind.Entities" />

  </alias>

 

Nicolas

 

-----Message d'origine-----
De : Clough, Samuel (USPC.PRG.Atlanta) [mailto:Samuel_Clough@princetonrg.com] 
Envoyé : jeudi 31 mai 2007 17:00
À : user-cs@ibatis.apache.org; tselke@liquidhub.com
Objet : RE: <typeAlias> support for C# Generics?

 

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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