PRB: Optimistic Concurrency Check Fails with SQL Text Field

• Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0

SYMPTOMS

Attempting to update the same record at the same time by two different clients produces an error for one of the clients, and the record is not updated. The following should occur:

"Runtime-error 40002 01503:[Microsoft][ODBC SQL Server Driver][SQL
Server]Optimistic concurrency check failed, the row was modified outside
of this cursor"

RESOLUTION

Place a timestamp field in the table and use a SQL Server stored procedure that compares the timestamp field to the one returned by the result set. An error will be returned by the stored procedure if an attempt is made to update the same record with a different timestamp.

STATUS

Microsoft is researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

The steps below illustrate the problem and the solution. You will need to run two instances of the project. To see the problem, click Command1, Command2, and Command3 in one instance of the project, and click Command1, Command2 and Command4 in the second instance of the project. Then click Command4 to update the record in the first instance.

To work around this problem, use the stored procedure by clicking Command1 in the first instance and then Command1 and Command5 in the second instance, followed by Command5 in the first instance. The stored procedure compares the original timestamp and refuses to update the field.

Steps to Reproduce Behavior

1. Modify the pub_info table in the pubs database so that it contains a timestamp field. Edit the first record. Use the following code in ISQL-W to accomplish this:

   
         Alter table pubs.dbo.pub_info add pub_name char(10) null,
              whattime timestamp null
    

   After you have run the above successfully in ISQL-W, run the following by itself in ISQL-W:

   
         Update pub_info set pub_name= "MSPress" where pub_id= "0736"
    

   The code above will insert a timestamp field in the table and a value in that field for the first record where the pub_id is 0736. If the first record has a different pub_id value, use that value instead. This will also place a value in the timestamp field.



2. Create the following stored procedure using ISQL-W:

   
         CREATE PROCEDURE updat_pub_info  @id char(4), @mytext text,
             @pname char(10), @thyme timestamp
         AS
         update pub_info
            set  pr_info= @mytext,
                pub_name= @pname
            where pub_id= @id and tsequal(@thyme,whattime)
    




3. Create a new project and, under References, check Microsoft Remote Data Objects 2.0.



4. Add six command buttons to the form and paste the following code in the General Declarations section of the form:

   
          Option Explicit
          Dim en As rdoEnvironment
          Dim rs As rdoResultset
          Dim cn As rdoConnection
          Dim qr As rdoQuery
          Dim sqlstr As String
          Dim mytime As Variant
   
          Private Sub Command1_Click()
           sqlstr = "select pub_id, pub_name, pr_info, whattime from pub_info"
           Set rs = cn.OpenResultset(sqlstr, rdOpenKeyset, _
              rdConcurRowVer, rdExecDirect)
           mytime = rs(3)  'needed to send the timestamp back to the procedure
          End Sub
         Private Sub Command2_Click()
           rs.Edit
           rs(1) = "testing"   'update the char field, change in 2nd instance
         End Sub
         Private Sub Command3_Click()
            rs(2) = "mmmmmmmmmm" 'update the text field,change in 2nd instance
         End Sub
         Private Sub Command4_Click()
            rs.Update
         End Sub
         Private Sub Command5_Click()
          'On Error GoTo myerr 'uncomment to trap error
             Set qr = cn.CreateQuery _
                ("", "{call updat_pub_info(?,?,?,?)}")
             qr.rdoParameters(0).Direction = rdParamInput
             qr.rdoParameters(1).Direction = rdParamInput
             qr.rdoParameters(2).Direction = rdParamInput
             qr.rdoParameters(3).Direction = rdParamInput
             qr(0) = "0736"
             qr(1) = "QUE"
             qr(2) = "This is a third text field"
             qr(3) = mytime  'variant type will compare to timestamp
             qr.Execute
             Exit Sub
             On Error GoTo 0
         myerr:
            MsgBox Err.number
         End Sub
   
         Private Sub Command6_Click()
           If Not (rs Is Nothing) Then
             rs.Close
           End If
           cn.Close
           Unload Me
         End Sub
   
         Private Sub Form_Load()
           Set en = rdoEnvironments(0)
           'change dsName to the data source name in your odbc administrator
           Set cn = en.OpenConnection(dsName:="mymachine", _
               Prompt:=rdDriverNoPrompt, _
               Connect:="uid=sa;pwd=;database=PUBS;")
           Command1.Caption = "resultset"
           Command2.Caption = "edit char field"
           Command3.Caption = "edit text field"
           Command4.Caption = "update"
           Command5.Caption = "update stor proc"
           Command6.Caption = "quit"
        End Sub
    




5. Run two instances of this project. You will want to save the project twice with different names or create two different executables to run.



6. Click Command1 and Command2 in the first instance, and Command1, Command2, and Command4 in the second instance. Click Command4 in the first instance and note that you get the error message indicated above.



7. Click Command1, Command2, and Command3 in the first instance, and Command1, Command2, and Command4 in the second instance. Click Command4 in the first instance and note that no error message is returned.
   
   If you change what rs(1) is set equal to in one of the applications, you will see that the second instance has updated pub_info, but the first instance has not, and no error message was returned.



8. To work around this problem, try clicking Command1 in the first instance. Click Command1 and Command5 in the second instance and then Command5 in the first instance. An error message is returned about the timestamp field if the error is not trapped.

Additional query words: blob multiuser kbVBp500 kbVBp600 kbdse kbDSupport kbVBp

Keywords : kbGrpVBDB
Version :
Platform : WINDOWS
Issue type : kbprb