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
Add a CustomValidator control to the page and set the following properties:
The ID of the control you are validating.
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.
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.
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