VB.net Disconnected Table

Question

I'm trying to load configuration settings into a set of DataTables and then disconnect from the database. I'm sure I am doing something wrong as the DataTables are empty afterwards. Here is the code:

From the top of the class:

'Set up Configuration DataTables
Dim dtDataAlerts As New DataTable

Running the Routine to get the data:

Public Sub ReadDataAlerts()
    'Read the configuration for the Data Alerts from the RDB
    dtDataAlerts = GetRecordSet("SELECT DataAlertGroups.DataAlertGroup_UID, DataAlertGroups.EmailGroup_UID, DataAlertGroups.EmailTemplate_UID, EmailTemplates.EmailTemplate_CustomSubject, EmailTemplates.EmailTemplate_CustomMessage FROM (DataAlertGroups INNER JOIN EmailGroups ON DataAlertGroups.EmailGroup_UID=EmailGroups.EmailGroup_UID) INNER JOIN EmailTemplates ON DataAlertGroups.EmailTemplate_UID=EmailTemplates.EmailTemplate_UID")
End Sub

The routine to get the DataTable

   Function GetRecordSet(SQLString As String) As DataTable

    'function used to run a query and return a disconnected DataTable

    Try


    'Create Dataset, Open Connection
    Dim dsPWC As New DataSet()
    Dim OleDbDataAdapter1 As System.Data.OleDb.OleDbDataAdapter = New System.Data.OleDb.OleDbDataAdapter(SQLString, sqlConn)
    sqlConn.Open()

    'Fill the Dataset with the PlantWatchConfiguration Table
    OleDbDataAdapter1.Fill(dsPWC, "CollectorAlertGroups")

    'Create Table from Dataset and iterate data
        Dim DT As New DataTable
        Dim DTClone As New DataTable

    DT = dsPWC.Tables(0)
        DTClone = DT.Clone

    'Close Connection
        sqlConn.Close()

        Return DTClone

    Catch ex As Exception
        WriteToLog(ex.Message, "GetRecordSet")
    End Try
End Function

I know the SQL is correct as I have already run it against the RDB and it produces results. I have a ton of logging to file in my code, so I am sure the database is connecting properly. (And other direct queries pull back data just fine)

But I am doing something wrong on the GetRecordSet function. I'm thinking that I am not properly cloning and disconnecting?

Anyway... I'm sure this is simple since I am not a coding expert :)

Thanks.

Answer 1

The error is exactly the Clone method . It clones the datatable structure, not the data.

DataTable.Clone: Clones the structure of the DataTable, including all DataTable schemas and constraints.

If you want the data you need to use the Copy method .

DataTable.Copy: Copies both the structure and data for this DataTable.

However, as I have said in my comment, you don't need to waste the memory of your PC in this way. ADO.NET is based on the disconnected model. The datatables present in the Dataset filled by the adapter are already disconnected from the database and you could return directly the table at index zero without any useless copy/clone.