The problem seems to be with a cloning a DataTable that has a column
expression that references its parent.
<xs:element name="DataFldSetName" msdata:ReadOnly="true"
msdata:Expression="Parent(Relation1).SpecName" type="xs:string"
msdata:targetNamespace="" minOccurs="0" />
Using Reflector, I found that the Clone method calls DataTable.Reset, which
calls DataTable.Reset. The Reset method removes all of the ParentRelations:
collection1 = this.ParentRelations;
num1 = collection1.Count;
while ((num1 > 0))
{
num1 = (num1 - 1);
collection1.RemoveAt(num1);
}
The expression itself is still copied from the source table to the clone.
As soon as an expression is set on a column, it is evaluated. The cloned
table does not have any parent relations, so the NullReferenceException is
generated.
Kirk Allen Evans
www.xmlandasp.net
Web Log: http://blogs.xmladvice.com/kaevans
-----Original Message-----
From: Moderated discussion of advanced .NET topics.
[mailto:[EMAIL PROTECTED] On Behalf Of Gary Davidson
Sent: Friday, January 23, 2004 7:04 AM
To: [EMAIL PROTECTED]
Subject: Re: [ADVANCED-DOTNET] DataTable.Clone and NullReferenceException
Try this
TypeDataTable dt = dv.Table as TypeDataTable;
DataSet ds = new DataSet();
ds.Merge(dt, true,MissingSchemaAction.Add);
return ds;
Gary Davidson
>From: Kirk Allen Evans <[EMAIL PROTECTED]>
>Reply-To: "Moderated discussion of advanced .NET topics."
><[EMAIL PROTECTED]>
>To: [EMAIL PROTECTED]
>Subject: [ADVANCED-DOTNET] DataTable.Clone and NullReferenceException
>Date: Thu, 22 Jan 2004 18:30:25 -0500
>
>I am using an API that exposes a DataView of a typed DataTable, I have no
>control over this API. The DataTable that I am trying to use already
>belongs to a typed DataSet. I need to import the DataTable to another
>DataSet to be able to work with it.
>
>Tried using ds.Merge(table). Internally, .Merge calls the .Clone method on
>the table being merged in. For some reason, .Clone throws a
>NullReferenceException when .Clone is called. I verified that the table
>has
>both rows and columns, and the code decompile for System.Data.DataTable in
>Reflector didn't show anything obvious that would cause the exception.
>
>//Calling code
>private DataSet GetDS(DataView dv)
>{
> DataTable dt = dv.Table;
> DataSet ds = new DataSet();
> ds.Merge(dt);
> return ds;
>}
>
>
>'Pseudo class
>Public Class fooTable
> Inherits DataTable
>
> Public Overrides Function ToString() As String
> Return Me.TableName & "foo"
> End Function
>
> Public Overrides Function Clone() As DataTable
> 'Following line throws the exception
> Dim dt As DataTable = MyBase.Clone()
>
> Dim cln As fooTable = CType(dt, fooTable)
> cln.TableName = Me.ToString()
> Return cln
> End Function
>End Class
>
>
>So, has anyone see a case where an inherited DataTable could throw a
>NullReferenceException in the .Clone method?
>
>===================================
>This list is hosted by DevelopMentorR http://www.develop.com
>Some .NET courses you may be interested in:
>
>NEW! Guerrilla ASP.NET, 26 Jan 2004, in Los Angeles
>http://www.develop.com/courses/gaspdotnetls
>
>View archives and manage your subscription(s) at http://discuss.develop.com
_________________________________________________________________
Check out the coupons and bargains on MSN Offers!
http://shopping.msn.com/softcontent/softcontent.aspx?scmId=1418
===================================
This list is hosted by DevelopMentorR http://www.develop.com
Some .NET courses you may be interested in:
NEW! Guerrilla ASP.NET, 26 Jan 2004, in Los Angeles
http://www.develop.com/courses/gaspdotnetls
View archives and manage your subscription(s) at http://discuss.develop.com
===================================
This list is hosted by DevelopMentor� http://www.develop.com
Some .NET courses you may be interested in:
NEW! Guerrilla ASP.NET, 26 Jan 2004, in Los Angeles
http://www.develop.com/courses/gaspdotnetls
View archives and manage your subscription(s) at http://discuss.develop.com
