How to: Validate Against Values in a Database for ASP.NET Server Controls

You can validate a user's entry against a database to be sure that what the user has entered is a recognized value. To do this, you must write code in a CustomValidator control that looks for data matches in a database.

To validate against a database

1. Add a CustomValidator control to the page and set the following properties:

   Property	Description
   ControlToValidate	The ID of the control you are validating.
   ErrorMessage, Text, Display	Properties that specify the text and location of the error or errors that will display if the validation fails. For details, see How to: Control Validation Error Message Display for ASP.NET Server Controls.

2. Create an event handler for the CustomValidator control's ServerValidate event. In the event handler, add code to look through the database and check the user's input against the dataset.

   Note
   If the user leaves a control blank, the control passes the comparison validation. To force the user to enter a value, add a RequiredFieldValidator control as well. For details, see How to: Validate Required Entries for ASP.NET Server Controls.

3. Add a test in your ASP.NET Web page code to check for validity. For details, see How to: Test Validity Programmatically for ASP.NET Server Controls.

   The following code example shows how you can validate a user's entry by looking it up in a database table. In this instance, the user has entered an e-mail address that is validated against e-mail addresses stored in a table. The custom validation logic loops through the rows in a table that is part of the dataset available to the page.

   Private Sub CustomValidator1_ServerValidate(ByVal _
      source As System.Object, ByVal args As _
      System.Web.UI.WebControls.ServerValidateEventArgs) _
      Handles CustomValidator1.ServerValidate
   
       Dim dv As DataView
       Dim dataset11 As New Data.DataSet
   
       dv = dataset11.Tables(0).DefaultView
   
       Dim datarow As DataRowView
       Dim txtEmail As String
       args.IsValid = False    ' Assume False
       ' Loop through table and compare each record against user's entry
       For Each datarow In dv
           ' Extract e-mail address from the current row
           txtEmail = datarow.Item("Alias").ToString()
           ' Compare e-mail address against user's entry
           If txtEmail = args.Value Then
               args.IsValid = True
               Exit For
           End If
       Next
   End Sub
   

   private void CustomValidator1_ServerValidate(object source, System.Web.UI.WebControls.ServerValidateEventArgs args)
   {
       DataView dv;
       DataSet dataSet11 = new DataSet();
   
       dv = dataSet11.Tables[0].DefaultView;
       string txtEmail;
       args.IsValid = false;    // Assume False
       // Loop through table and compare each record against user's entry
       foreach (DataRowView datarow in dv)
       {
           // Extract e-mail address from the current row
           txtEmail = datarow["Alias "].ToString();
           // Compare e-mail address against user's entry
           if (txtEmail == args.Value)
           {
               args.IsValid = true;
           }
       }
   }
   

See Also

Concepts

Types of Validation for ASP.NET Server Controls

Other Resources

Validation ASP.NET Controls