Text Box

planoie · February 1st, 2006, 12:53 AM

The error message says it all: "Use 'Is' operator to compare two reference types."

If currentValue Is System.DBNull Then

in your case, you want when it Is NOT, thus:

If Not currentValue Is System.DBNull Then

-Peter

praveen_haridas · February 1st, 2006, 01:24 AM

Once again thanks for your answer Peter. Apart from the error, I had problems with the output not being displayed. I got rid of the error as per your suggestion. I'm not sure where I'm going wrong with the code. I'm not even sure if the cod eis right or not.

Could you please give your valuable suggestions.

Thanks in advance

Regards

Praveen

planoie · February 3rd, 2006, 11:30 AM

What problems are you having now?

-Peter

praveen_haridas · February 4th, 2006, 06:02 AM

The problem is that when I compile the following code, it doesn't show me any output. The database is connected and the text box (read-only) is also displayed. But the desired output is not obtained.

Code:

<%@ Import namespace="system.data.oledb"%>
<%@ Import namespace="system.data"%>
<%@ Page Language="vb"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
    <HEAD>
        <title>dbtextbox</title>
        <meta name="GENERATOR" content="Microsoft Visual Studio .NET 7.1">
        <meta name="CODE_LANGUAGE" content="Visual Basic .NET 7.1">
        <meta name="vs_defaultClientScript" content="JavaScript">
        <meta name="vs_targetSchema" content="http://schemas.microsoft.com/intellisense/ie5">
    </HEAD>
    <body MS_POSITIONING="GridLayout">
        <form id="Form1" method="post" runat="server">
            <asp:TextBox id="dumb" style="Z-INDEX: 100; LEFT: 144px; POSITION: absolute; TOP: 96px" runat="server"
                Width="128px" ReadOnly="True"></asp:TextBox>
         </form>     
<script runat="server" language="vb">
sub rate_capture(o as object, e as eventargs)
         dim dtrate as oledbdatareader
         dim con1 as new oledbconnection("Provider=MSDAORA.1;User ID=SCOTT;Password=TIGER;Data Source=HARI")
         con1.open()
         dim cmd1 as new oledbcommand("select rate from test1 where car_code='CAMXL04'",con1)
         dtrate=cmd1.executereader()
         dtrate.close()
         con1.close()

         dumb.Text = String.Empty
        If dtrate.Read() Then
            Dim currentValue As Object = dtrate("rate")
                If not currentValue is System.DBNull.Value Then 
                        dumb.Text = currentValue.ToString().Trim()
                End If
        End If
    end sub
        </script>
    </body>
</HTML>

What I wanted to know is, is this code right in the first place? I'm not pretty much sure about the code. The second thing is that, the contents of this text box is supposed to change according to a drop down list (which I have not included in the above code). Therefore in the query I have given all the conditions that it needs to satisfy to retrieve the data that I want. The following is the table
Table Test1
Name Type
car_code varchar2(8)--> This is the code that I've specified in the query
descript varchar2(50)
rate varchar2(4)--> This is what I want to display in the read only text box according to the above car_code

The car_code is as I've shown in the query "CAMXL04" and the corresponding rate can be, say, 65. The descript could be anything. The only thing that matters to me right now is to display the rate according to the car_code.

Thanks in advance,

Regards,

Praveen

planoie · February 4th, 2006, 08:48 AM

Try this (I've cleaned up the page a bit to simplify the post:

Code:

<%@ Import namespace="system.data.oledb"%>
<%@ Import namespace="system.data"%>
<%@ Page Language="vb"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
    <HEAD>
        <title>dbtextbox</title>
    </HEAD>
    <body>
        <form id="Form1" method="post" runat="server">
            <asp:dropdownlist id="ddlCars" runat="server"
               OnSelectedIndexChanged="ddlCars_SelectedIndexChanged" />
            <asp:TextBox id="txtRate" runat="server" ReadOnly="True" />
         </form>     
<script runat="server" language="vb">
Dim strConn As String = "Provider=MSDAORA.1;User ID=SCOTT;Password=TIGER;Data Source=HARI"
Sub Page_Load(sender As Object, e As EventArgs)
    If Not IsPostback Then
        dim con as new oledbconnection(strConn)
        dim cmd as new oledbcommand("select car_code,descript from car_code",con)
        con.open()
        ddlCars.datasource=cmd.executereader()
        ddlCars.datatextfield="descript"
        ddlCars.datavaluefield="car_code"
        ddlCars.databind()
        con.close()
    End If
End Sub
Sub ddlCars_SelectedIndexChanged(sender As Object, e As EventArgs)
    Dim strSql As String = "select rate from test1 where car_code='{0}'"
    Dim currentValue As Object
    dim con1 as new oledbconnection(strConn)
    dim cmd1 as new oledbcommand(String.Format(strSql, ddlCars.SelectedValue), con1)
    con1.open()
    currentValue = cmd1.ExecuteScalar()
    con1.close()
    If Not currentValue Is System.DBNull.Value Then 
        txtRate.Text = currentValue.ToString().Trim()
    End If
End Sub
        </script>
    </body>
</HTML>

-Peter