Question

I am trying to delete entries by ID. I want to notify user that ID they try to delete doesn’t exist. It doesn’t create any problems, but I want to make everything clear.

How to do that? Do I have to use SQL string to do so?

I am using MS Access 2007 and this is how I delete item:

string SQL = "DELETE FROM PersonalData WHERE DataID = " + txtEntryID.Text;

private void DeleteData(string SQL)
{
    // Creating an object allowing me connecting to the database.
    // Using parameters in command will avoid attempts of SQL injection.
    OleDbConnection objOleDbConnection = new OleDbConnection();
    // Creating command object.
    objOleDbConnection.ConnectionString =
        "Provider=Microsoft.ACE.OLEDB.12.0;" +
        "Data Source=" + filePath + ";" +
        "Persist Security Info=False;" +
        "Jet OLEDB:Database Password=" + pass + ";";
    OleDbCommand objOleDbCommand = new OleDbCommand();

    objOleDbCommand.CommandText = SQL;

    // Assigning a connection string to the command.
    objOleDbCommand.Connection = objOleDbConnection;

    try
    {
        // Open database connection.
        objOleDbConnection.Open();
        objOleDbCommand.ExecuteNonQuery();
    }
    catch (Exception ex)
    {
        // Displaying any errors that 
        // might have occured.
        MessageBox.Show("Error: " + ex.Message);
    }
    finally
    {
        // Close the database connection.
        objOleDbConnection.Close();
    }

    // Refreshing state of main window.
    mainWindow.DisplayFileContent(filePath);

    MessageBox.Show("Data was successfully deleted.");

    // Clearing text box field.
    txtEntryID.Clear();
}

Answer 1

In VBA code, you could use the DCount() function.

You can also just delete the records with a SQL statement and inform the user after the fact; from the user’s point of view there’s no difference:

Dim id As Long

id = GetAnIdFromTheUser()

With CurrentDb
    Do
        .Execute "DELETE FROM [TableName] WHERE ID = " & id
        If .RecordsAffected > 0 Then
            Goto Done
        End If
        MsgBox "That ID doesn't exist; please try another."
        id = GetAnIdFromTheUser()
    Loop
Done:
    .Close
End With

EDIT:

In ADO.NET you can follow the same approach by examining the return value of ExecuteNonQuery. For example, you could declare your function as bool TryDeleteData(string SQL) and do something like

...
if (objOleDbCommand.ExecuteNonQuery() == 0)
    return false;
...