validate textbox value against a database

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VB

ASP.NET

Hi I want to validate my textbox value against a database.
when user input value in texbox , i want to check it against my database value.
if value exists in database, user is allowed to input that value , else shows an error, that value doesn't exists.
Can anyone have any sample code. how to do this kind of validation.
Any help is appreciated.

Author's Update:

I am validating my textbox using below function, but it wasn't validating textbox value.
Appreciate for any help to find what i am missing in my code.

VB Code:

Protected Sub ValidateRecipe(ByVal source As System.Object, ByVal args As System.Web.UI.WebControls.ServerValidateEventArgs) Handles CustomValidator1.ServerValidate
       Dim con11 As New SqlConnection(ConfigurationManager.ConnectionStrings("FConnectionString").ConnectionString)
       con11.Open()
       Dim ds11 As New DataSet()
       Dim ada11 As New SqlDataAdapter("P_FN_PR_ValidRecipe", con11)
       ada11.SelectCommand.CommandType = CommandType.StoredProcedure
       ada11.Fill(ds11, "P_FN_PR_ValidRecipe")
       Dim dv As DataView
       dv = ds11.Tables(0).DefaultView
       Dim datarow As DataRowView
       Dim txtRecipe As String
       args.IsValid = False
       For Each datarow In dv
           txtRecipe = datarow.Item("port_recipe_num").ToString()
           If txtRecipe = args.Value Then
               args.IsValid = True
               Exit For
           End If
       Next
   End Sub

Stored Procedure:

ALTER PROCEDURE [DBO].P_FN_PR_ValidRecipe
AS
select DISTINCT port_recipe_num
from FN_Portions
RETURN

ASPX Code:

<asp:TextBox ID="TextBox1" runat="server" MaxLength="4" Width="150px"
                        Height="16px" AutoPostBack="True" CausesValidation="True"></asp:TextBox>
                    <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="TextBox1"
                        ErrorMessage="* required" ForeColor="#CC0000" Display="Dynamic"></asp:RequiredFieldValidator>
                    <br />
                    <asp:CustomValidator ID="CustomValidator1" runat="server" ControlToValidate="TextBox1"
                        OnServerValidate="ValidateRecipe" Display="Dynamic" ForeColor="#CC0000"
                        ErrorMessage="No Recipe # Exist !"></asp:CustomValidator>