Microsoft KB Archive/310367

= Error message when you use CommandBuilder: &quot;An unhandled exception of type 'System.NullReferenceException' occurred&quot; =

Article ID: 310367

Article Last Modified on 12/11/2006

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APPLIES TO


 * Microsoft ADO.NET 2.0
 * Microsoft .NET Framework 1.1 Service Pack 1
 * Microsoft Visual Basic .NET 2002 Standard Edition
 * Microsoft Visual C# .NET 2002 Standard Edition
 * Microsoft Visual J# .NET 2003 Standard Edition
 * Microsoft Visual Basic .NET 2003 Standard Edition
 * Microsoft Visual Basic 2005
 * Microsoft Visual C# .NET 2003 Standard Edition
 * Microsoft Visual C# 2005
 * Microsoft Visual J# .NET 2003 Standard Edition

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This article was previously published under Q310367



This article refers to the following Microsoft .NET Framework Class Library namespaces:
 * System.Data.OleDb
 * System.Data.SqlClient



SYMPTOMS
If you use the CommandBuilder object to explicitly get commands for the DataAdapter object as follows: da.InsertCommand = cb.GetInsertCommand and then run the following Visual Basic .NET code cb.DataAdapter = Nothing or the following Visual C# .NET code cb.DataAdapter = null; the commands that you add to the DataAdapter are deleted, and you receive the following error message:

An unhandled exception of type 'System.NullReferenceException' occurred in .exe

Additional information: Object reference not set to an instance of an object.



CAUSE
CommandBuilder deletes the commands that it generates when it is disassociated from a DataAdapter. CommandBuilder and DataAdapter are linked; when they are unlinked or disassociated, the commands are nulled. This problem does not affect commands that you build from the beginning (from scratch).



RESOLUTION
Use one of the following methods to resolve this problem:
 * Do not disassociate the CommandBuilder from the DataSet.
 * Build the commands yourself, either in code or through Visual Data Tools.



STATUS
This behavior is by design.



Steps to Reproduce the Behavior
 Create a new Visual Basic .NET Windows Application project. Form1 is added to the project by default. Add a Button control to Form1.  Switch to Code view, and add the following code to the top of the Code window: Imports System.Data.OleDb Imports System.Data.SqlClient   Add the following code to the Click event of the Button: Dim con As New SqlConnection(&quot;server=myserver;uid=sa;pwd=mypassword;&quot; & _                                    &quot;database=northwind&quot;) Dim da As New SqlDataAdapter(&quot;Select * From Customers&quot;, con) Dim cb As New SqlCommandBuilder(da) Dim cmdInsert As New SqlCommand( _              &quot;Insert Into Customer (CustomerID) Value ('AAAAA')&quot;, con) da.InsertCommand = cmdInsert da.UpdateCommand = cb.GetUpdateCommand da.DeleteCommand = cb.GetDeleteCommand Debug.WriteLine(da.InsertCommand.CommandText) Debug.WriteLine(da.DeleteCommand.CommandText) cb.DataAdapter = Nothing ' Comment out this line to avoid the error. cb = Nothing Debug.WriteLine(da.InsertCommand.CommandText) Debug.WriteLine(da.DeleteCommand.CommandText) 'Error occurs here.  Modify your connection string as appropriate for your environment.</li> Press the F5 key to compile and to run the application.</li></ol>

Keywords: kberrmsg kbtshoot kbsqlclient kbsystemdata kbprb KB310367

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