11: Security in Visual Basic .NET

Encode QR Code in Visual Basic .NET 11: Security

11: Security
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ErrorHandler: GeneralError("GroupName.DeleteRecord", Err.GetException( )) TransactionRollback( ) Return False End Function
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After confirming the delete with the user, a quick check determines whether the group is still being used somewhere in the UserName table. If everything checks out fine, the record is deleted using a SQL DELETE statement. Since we need to delete data in two tables, I wrapped it all up in a transaction. If an error does occur, the error handler at the end of the routine will roll back the transaction through TransactionRollback.
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If you have a background in database development, you have already seen the flaw in the delete code. Although I take the time to verify that the record is not in use before deleting it, it s possible that some other user will use it between the time I check the record s use and the time when I actually delete it. Based on the code and database configuration I ve presented so far, it would indeed be an issue. When I designed this system, I expected that a single librarian would manage administrative tasks such as this, so I didn t worry about such conflicts and race conditions. If you are concerned about the potential for deleting in-use records through code like this, you can enable referential integrity on the relationships in the database. I established a relationship between the GroupName.ID and UserName.GroupID fields, but it was for informational purposes only. You can reconfigure this relationship to have SQL Server enforce the relationship between the tables. If you do this, it will not be possible to delete an in-use record; an error will occur in the program when you attempt it. That sounds good, and it is, but an overuse of referential integrity can slow down your data access. I will leave this configuration choice up to you.
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When the user is done making changes to the record, a click on the OK button pushes the data back out to the database. The ActOK_Click event handler verifies the data, and then saves it.
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If (ValidateFormData( ) = False) Then Return If (SaveFormData( ) = False) Then Return Me.DialogResult = Windows.Forms.DialogResult.OK
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The ValidateFormData method does some simple checks for valid data, such as requiring that the user enter the security group name, and that it is unique. If everything looks good, the SaveFormData routine builds SQL statements that save the data.
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Private Function SaveFormData( ) As Boolean ' ----- The user wants to save changes. ' Return True on success.
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Dim sqlText As String Dim newID As Integer = -1 On Error GoTo ErrorHandler ' ----- Prepare to save the data. Me.Cursor = Windows.Forms.Cursors.WaitCursor TransactionBegin( ) ' ----- Save the data. If (ActiveID = -1) Then ' ----- Create a new entry. sqlText = "INSERT INTO GroupName (FullName) " & _ "OUTPUT INSERTED.ID VALUES (" & _ DBText(Trim(RecordFullName.Text)) & ")" newID = CInt(ExecuteSQLReturn(sqlText)) Else ' ----- Update the existing entry. newID = ActiveID sqlText = "UPDATE GroupName SET FullName = " & _ DBText(Trim(RecordFullName.Text)) & _ " WHERE ID = " & ActiveID ExecuteSQL(sqlText) End If ' ----- Clear any existing security settings. sqlText = "DELETE FROM GroupActivity " & _ "WHERE GroupID = " & newID ExecuteSQL(sqlText) ' ----- Save the selected security settings. For Each itemChecked As ListItemData In _ ActivityList.CheckedItems sqlText = "INSERT INTO GroupActivity (GroupID, " & _ "ActivityID) VALUES (" & newID & ", " & _ itemChecked.ItemData & ")" ExecuteSQL(sqlText) Next itemChecked ' ----- Complete all changes. TransactionCommit( ) ActiveID = newID ' ----- This change may affect this user. If (LoggedInGroupID = ActiveID) Then _ ReprocessSecuritySet( ) ' ----- Success. ActiveID = newID Me.Cursor = Windows.Forms.Cursors.Default Return True
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