在vb.net的下拉菜单中添加数据库中的数据

Question

I have a drop down list for cities, and I have cities in my database that I want to populate to a drop down list.

On the Page load made an sql connection

 Dim s As String = "Connection String"
 sqlconn = New SqlConnection(s) 

Now on the drop down load I have a query which is working fine. How to add results from the database query to the drop down?

   Protected Sub Citydropdown_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Citydropdown.Load

        sqlCmd = New SqlCommand("select City from usrRegister_aunthentication", sqlconn)
        If sqlconn.State = Data.ConnectionState.Closed Then
            sqlconn.Open()
        End If
        Dim i As String = sqlCmd.ExecuteReader()

        If sqlconn.State = Data.ConnectionState.Open Then
            sqlconn.Close()
        End If
    End Sub

Also, sometimes the same city is repeated. How do I only show each city once?

Answer 1

Do not use ExecuteNonQuery to fetch the result (rows). Use ExecuteReader to obtains the reader instance.

Dim dataReader as SqlDataReader 
dataReader = sqlCmd.ExecuteReader()
While dataReader.Read
  ' Write code to insert an Item into dropdownlist
  DropDownItem1.Items.Add(dataReader("City").ToString())
End While
dataReader.Close()

Answer 2

You could also try this. It is a line or two less.

Using dr = sqlCmd.ExecuteReader()
While dr.Read
     ' Write code to insert an Item into dropdownlist
     DropDownItem1.Items.Add(dr("City").ToString())
End While
End Using