Question

I am currently working on an asp.net web page with a GridView displaying a table from a database. This GridView has 4 DropDownLists that will be used to filter the data shown on the GridView. When the page loads 4 Sub routines are run, each one connecting to the database with a select statement to fill the DropDownList with relevant filter headings.

Initially, I had one connection with a loop that populated all of the drop downs but these contained duplicates. I then split the filling of each DDL so that the select statements could contain DISTINCT.

I would like (and am sure there is a way here) to be able to populate all of the DDLs with data from one connection.

Code for one connection:

        Protected Sub FillDepDDL()

        Dim conn As New SqlConnection()
        conn.ConnectionString = WebConfigurationManager.ConnectionStrings("TestDBConnectionString").ConnectionString

        Dim connection As New SqlConnection(conn.ConnectionString)
        connection.Open()

        Const FillAllQS As String = "SELECT DISTINCT [Department] FROM [Employees]"

        Dim command As New SqlCommand(FillAllQS, connection)

        Dim reader As SqlDataReader = command.ExecuteReader()

        Dim sel As New ListItem
        sel.Text = "Please Select"
        sel.Value = "*"
        DDLDepartment.Items.Add(sel)
        While reader.Read

            Dim Deplist As New ListItem()
            Deplist.Value = reader("Department")
            Deplist.Text = reader("Department")
            DDLDepartment.Items.Add(Deplist)

        End While
        reader.Close()
        conn.Close()

    End Sub

The other 3 column names: FirstName > DDLFN, LastName > DDLLN, Wage > DDLWag.

This is only a test DB and the princibles learned here will be applied to a larger live project.

I’m sure some guru will be able to work this out easily but I just can’t get my head round it even after hours of searching.

Thanks in advance.

Answer 1

I’m adding this in as answer because I cannot format it in a comment, but this doesn’t answer the original question of how to write the sql to return all three distinct result sets. Instead, it answers how to rewrite the code you have above so that connections are properly disposed of in case of an exception.

Protected Sub FillDepDDL()
      Dim Deplist As ListItem
      Dim sel As New ListItem
      sel.Text = "Please Select"
      sel.Value = "*"
      DDLDepartment.Items.Add(sel)  

      Using conn As New SqlConnection(WebConfigurationManager.ConnecitonString("TestDBConnectionString").ConnectionString)          
           Using cmd As New SqlCommand("SELECT DISTINCT [Department] FROM [Employees]", conn)
                conn.Open()

                Using reader = cmd.ExecuteReader()
                     While reader.Read
                          Deplist = New ListItem()
                          Deplist.Value = reader("Department")
                          Deplist.Text = reader("Department")
                          DDLDepartment.Items.Add(Deplist)
                     End While
                End Using       
           End Using    
      End Using
 End Sub

I don’t see any reason for you to try to return all three results in a single query. That will just make your code unnecessarily complicated just to save a millisecond or two. Connection pooling handles the creation of connections on the database server for you, so opening a new connection in your code is very fast.