Generic Class: Passing Data Type to Placeholder

[Etienne-Louis Nicolet]

I have a generic class defined as follows:

Public Class SqlArgument(Of TDataType)

Private _values as List(Of TDataType)

Public Property Values() As List(Of TDataType)
Get
Return _values
End Get
Set(ByVal pValues As List(Of TDataType))
_values = pValues
End Set

Public Sub New()
Me.Values = New List(Of TDataType)
End Sub

....

End Class


Given the DataType property of a (strongly typed) DataTable I'd like to
create a new instance of SqlArgument with the data type of the appropriate
table column. I thought about something like

Sub TestArgument(pC olumn as System.Data.Dat aColumn)
...
Dim s As new SqlArgument(Of pColumn.DataTyp e)
...
End Sub

but obviously this does not work. Can anybody give me a hint on how to do
this?

Many thanks for your suggestions,
Etienne

[Mattias Sjögren]

Re: Generic Class: Passing Data Type to Placeholder

>Given the DataType property of a (strongly typed) DataTable I'd like to

>create a new instance of SqlArgument with the data type of the appropriate
>table column. I thought about something like
>
>Sub TestArgument(pC olumn as System.Data.Dat aColumn)
...
Dim s As new SqlArgument(Of pColumn.DataTyp e)
...
>End Sub
>
>but obviously this does not work. Can anybody give me a hint on how to do
>this?

You have to go the Reflection route if you want to do this. You can
instantiate the right generic type using Type.MakeGeneri cType and then
an object from that type with Activator.Creat eInstance. But know that
once you've started using Reflection, it's hard to do something
without it, and the code quickly gets pretty ugly.

What are you actually going to do with the s variable once you've
created the instance?


Mattias

--
Mattias Sjögren [C# MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

[Marc Gravell]

Re: Generic Class: Passing Data Type to Placeholder

Can I just say: look at LINQ-to-SQL; that is exactly what it does for
you. You might be able to save a lot of effort...

Marc

[Etienne-Louis Nicolet]

Re: Generic Class: Passing Data Type to Placeholder

Dear Marc,

I bought a book on LINQ yesterday and will have a look at it. Thanks for the
tip!

Kind regards,
Etienne

"Marc Gravell" <marc.gravell@g mail.comwrote in message
news:%23$TZr1H% 23IHA.2232@TK2M SFTNGP05.phx.gb l...

Can I just say: look at LINQ-to-SQL; that is exactly what it does for you.
You might be able to save a lot of effort...
>
Marc

[Etienne-Louis Nicolet]

Re: Generic Class: Passing Data Type to Placeholder


"Mattias Sjögren" <mattias.dont.w ant.spam@mvps.o rgwrote in message
news:eftinBH%23 IHA.3656@TK2MSF TNGP03.phx.gbl. ..

Given the DataType property of a (strongly typed) DataTable I'd like to
>>create a new instance of SqlArgument with the data type of the appropriate
>>table column. I thought about something like
>>
>>Sub TestArgument(pC olumn as System.Data.Dat aColumn)
> ...
> Dim s As new SqlArgument(Of pColumn.DataTyp e)
> ...
>>End Sub
>>
>>but obviously this does not work. Can anybody give me a hint on how to do
>>this?

>
You have to go the Reflection route if you want to do this. You can
instantiate the right generic type using Type.MakeGeneri cType and then
an object from that type with Activator.Creat eInstance. But know that
once you've started using Reflection, it's hard to do something
without it, and the code quickly gets pretty ugly.
>
What are you actually going to do with the s variable once you've
created the instance?
>
>
Mattias
>
--
Mattias Sjögren [C# MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
Please reply only to the newsgroup.

Dear Mattias,

I tried to figure out how to use Reflection as recommended. I think i got
the first part:

Sub TestArgument(pC olumn as System.Data.Dat aColumn)
Dim generic As System.Type = GetType(SqlArgu ment(Of ))
Dim typeArgs() As Type = {pColumn.DataTy pe}
Dim constructed As Type = generic.MakeGen ericType(typeAr gs)
....
End Sub
However, I did not get along with the VB help on Activator.Creat eInstance.
Would you mind giving me a hint how the code should look like?

Many thanks & kind regards,
Etienne