Error when you try to call the Prepare method before you add parameters: "An unhandled exception of type 'System.Data.SqlClient.SqlException' occurred in system.data.dll"

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Article ID: 310368 - View products that this article applies to.
This article was previously published under Q310368
This article has been archived. It is offered "as is" and will no longer be updated.
For a Microsoft Visual C# .NET version of this article, see 311348.

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

When you create a parameterized command against Microsoft SQL Server 7.0, if you call the Prepare method before you add parameters to the command, you receive the following error message:
An unhandled exception of type 'System.Data.SqlClient.SqlException' occurred in system.data.dll.
Additional information: System error.
This problem does not occur in SQL Server 2000.

CAUSE

This problem occurs in SQL Server 7.0 because, by design, you cannot run the Prepare method before you add parameters. This applies to most database systems.

SQL Server 2000 does not generate the above-mentioned exception because it does not run Prepare until the first command is executed. This optimization prevents the overhead of Prepare if no commands are subsequently executed.

RESOLUTION

To resolve this problem, do not call the Prepare method until after you add the parameters.

MORE INFORMATION

Steps to Reproduce the Behavior

The sample code to follow uses the Region table of the Northwind sample database.
  1. Start Microsoft Visual Studio .NET.
  2. Create a new Visual Basic Windows Application project. Form1 is added to the project by default.
  3. Make sure that your project contains a reference to the System.Data namespace, and add a reference to this namespace if it does not.
  4. Place a Button control on Form1. Change the Name property of the button to btnTest, and change the Text property to Test.
  5. Use the Imports statement on the System, System.Data.OleDb, and System.Data.SqlClient namespaces so that you are not required to qualify declarations in those namespaces later in your code. Add the following code to the "General Declarations" section of Form1:
    Imports System
    Imports System.Data.OleDb
    Imports System.Data.SqlClient
    					
  6. Add the following code to the Code window after the "Windows Form Designer generated code" region.

    Note You must change User ID <username> and password =<strong password> to the correct values before you run this code. Make sure that User ID has the appropriate permissions to perform this operation on the database.
        Private Sub btnTest_Click(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles btnTest.Click
            Dim myConnString As String = _
                "User ID=<username>;password=<strong password>;Initial Catalog=Northwind;Data Source=myServer"
            Dim id As Integer = 25
            Dim desc As String = "myFirstRegion"
            Dim rConn As SqlConnection = New SqlConnection(myConnString)
            rConn.Open()
            Dim command As SqlCommand = New SqlCommand("", rConn)
            command.CommandText = "insert into Region (RegionID, RegionDescription)" & _
                                  "values (@id, @desc)"
    
            'SQL Server 7.0 throws an exception here.
            'Comment the following line to resolve this problem against SQL Server 7.0.
            command.Prepare()
    
            command.Parameters.Add("@id", SqlDbType.Int, 4)
            command.Parameters.Add("@desc", SqlDbType.Char, 50)
            'You can call Prepare after you set up CommandText and parameters.
            command.Prepare() 
    
            command.Parameters(0).Value = id
            command.Parameters(1).Value = desc
            command.ExecuteNonQuery()
            MessageBox.Show("Updated Successfully")
        End Sub
    					
  7. Modify the connection string (myConnString) as appropriate for your environment.
  8. Save your project. On the Debug menu, click Start to run your project.
  9. Click Test. If you are connected to a SQL Server 7.0 database, the code generates the above-mentioned exception.

    If you are connected to a SQL Server 2000 database, the code runs properly, and the "Updated Successfully" message box appears.
  10. To resolve this problem against SQL Server 7.0, comment out the call to command.Prepare that precedes the code to add the parameters, and then run the project again.

REFERENCES

For more information on ADO.NET objects and syntax, refer to the following Microsoft .NET Framework Software Development Kit (SDK) documentation:
Accessing Data with ADO.NET
http://msdn2.microsoft.com/en-us/library/e80y5yhx(vs.71).aspx

Properties

Article ID: 310368 - Last Review: February 28, 2014 - Revision: 2.8
APPLIES TO
  • Microsoft ADO.NET 2.0
  • Microsoft ADO.NET (included with the .NET Framework)
  • Microsoft Visual Basic .NET 2002 Standard Edition
  • Microsoft Visual Basic .NET 2003 Standard Edition
  • Microsoft Visual Basic 2005
  • Microsoft SQL Server 7.0 Standard Edition
Keywords: 
kbnosurvey kbarchive kbtshoot kberrmsg kbnofix kbprb kbsqlclient kbsystemdata KB310368

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