populate textbox from SQL query, after selection at dropdownlist

Question

May i have a working sample on how to retrieve records from a DB & populate the relevant textboxes after a selection at a dropdownlist. What i have is definitely not working & im working on VS 2008. Can anyone show me the way?

What i have:

    Dim myConn As New SqlConnection
    Dim myCmd As New SqlCommand
    Dim dtrReader As SqlDataReader

    myConn.ConnectionString = ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString
    myCmd = myConn.CreateCommand

    myCmd.CommandText = "SELECT * FROM Product WHERE product_id = '" & DropDownList2.Text & "'"
        'myCmd.CommandType = CommandType.Text

        'populate controls from DB
        'myCmd.Parameters.Add(New SqlParameter("@product_id", a))
        myCmd.Parameters.Add(New SqlParameter("@product_name", (txtProductName2.Text)))
        myCmd.Parameters.Add(New SqlParameter("@product_title", txtProductTitle2.Text))
        myCmd.Parameters.Add(New SqlParameter("@product_desc", txtProductDescription2.Text))
        myCmd.Parameters.Add(New SqlParameter("@product_author", txtProductAuthor2.Text))

        mycmd.Dispose()
        myConn.Close()
        myConn.Dispose()

ChrisWue · Accepted Answer · 2011-12-31 21:34:20Z

The parameters collection of the command is to pass parameters to the query and not fill in variables from a result. First you should do the query and then read the results and fill your controls:

' build the query with the product id as paramter
myCmd.CommandText = "SELECT product_name, product_title, product_desc, product_author FROM Product WHERE product_id = @product_id"
' add the parameter so the SqlCommand can build the final query
myCmd.Parameters.Add(New SqlParameter("@product_id", (DropDownList2.Text)))

' run the query and obtain a reader to get the results
Dim reader As SqlDataReader = myCmd.ExecuteReader()

' check if there are results
If (reader.Read()) Then
     ' populate the values of the controls
     txtProductName2.Text = reader(0)
     txtProductTitle2.Text = reader(1)
     txtProductDescription2.Text = reader(2)
     txtProductAuthor2.Text = reader(3)
End If

This is just a quick example and contains no error handling but should work.

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