System.NullReferenceException occurs when you use the CommandBuilder object
This article helps you resolve the System.NullReferenceException
exception that occurs when you use the CommandBuilder
object.
Original product version: Visual Basic .NET
Original KB number: 310367
Symptoms
If you use the CommandBuilder
object to explicitly get commands for the DataAdapter
object as follows:
da.InsertCommand = cb.GetInsertCommand
Then, run the following Visual Basic .NET code:
cb.DataAdapter = Nothing
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 app_name.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.
Resolution
Use one of the following methods to resolve this problem:
- Do not disassociate the
CommandBuilder
from theDataSet
. - 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("server=myserver;uid=sa;pwd=mypassword;" & _ "database=northwind") Dim da As New SqlDataAdapter("Select * From Customers", con) Dim cb As New SqlCommandBuilder(da) Dim cmdInsert As New SqlCommand( _ "Insert Into Customer (CustomerID) Value ('AAAAA')", 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.
Press the F5 to compile and to run the application.