Custom Validation Check Duplicate Data

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I'm still trying to get my validation to work correctly. So far if a user enters in a Salesman Code that exists in the database it displays the error message when tabbing off the field. The Salesman Code field is also required so I can't get this validator to work either with the customer validator that checks duplicates. What I am looking for is when a user does not enter a Salesman Code for the error to appear and not let the user submit the form. If the user enters a Salesman Code that exists in the database the error message will be displayed and the user should not be allowed to submit the form. Any help or examples would be appreciated. Below is my code that I have using VB.

Below is my aspx page:

ASP.NET Syntax (Toggle Plain Text)
<%@ Page Language="VB" %>  
<%@ Register TagPrefix="custom" Namespace="myControls" %>  
<%@ Import Namespace="System.Data.SqlClient" %>  
<%@ Import Namespace="System.Web.Configuration" %>  
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"   
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">  
<script runat="server">  
 
 
    ''' Validation function that is called on both the client and server   
 
    Protected Sub AjaxValidator1_ServerValidate(ByVal source As Object, ByVal args As ServerValidateEventArgs)   
        If Salesman_CodeExists(args.Value) Then   
            args.IsValid = False  
        Else   
            args.IsValid = True  
            Me.btnSubmit.Attributes.Add("onclick", "alert('Please try a different Salesman Code!');return false;")   
        End If   
    End Sub   
 
    ''' <summary>  
    ''' Returns true when user name already exists   
    ''' in Users database table   
    ''' </summary>  
    Private Function Salesman_CodeExists(ByVal Salesman_Code As String) As Boolean   
        Dim conString As String = WebConfigurationManager.ConnectionStrings("PennerConnectionString").ConnectionString   
        Dim con As New SqlConnection(conString)   
        Dim cmd As New SqlCommand("SELECT COUNT(*) FROM tblSalesman WHERE Salesman_Code=@Salesman_Code", con)   
        cmd.Parameters.AddWithValue("@Salesman_Code", Salesman_Code)   
        Dim result As Boolean = False  
        Using con   
            con.Open()   
            Dim count As Integer = CType(cmd.ExecuteScalar(), Integer)   
            If count > 0 Then   
                result = True  
            Else   
            End If   
        End Using   
        Return result   
    End Function   
 
 
    ''' Insert new user name to Users database table   
 
    Protected Sub btnSubmit_Click(ByVal sender As Object, ByVal e As EventArgs)   
        Dim conString As String = WebConfigurationManager.ConnectionStrings("PennerConnectionString").ConnectionString   
        Dim con As New SqlConnection(conString)   
        Dim cmd As New SqlCommand("INSERT tblSalesman (Salesman_Code,Salesman_LastName) VALUES (@Salesman_Code,@Salesman_LastName)", con)   
        cmd.Parameters.AddWithValue("@Salesman_Code", txtSalesman_Code.Text)   
        cmd.Parameters.AddWithValue("@Salesman_LastName", txtSalesman_LastName.Text)   
        Using con   
            con.Open()   
            cmd.ExecuteNonQuery()   
        End Using   
        txtSalesman_Code.Text = String.Empty   
        txtSalesman_LastName.Text = String.Empty   
    End Sub   
</script>  
<html xmlns="http://www.w3.org/1999/xhtml" >  
<head id="Head1" runat="server">  
    <title>Show AjaxValidator</title>  
</head>  
<body>  
    <form id="form1" runat="server">  
    <div>  
 
    <asp:Label  
        id="lblSalesman_Code"  
        Text="Salesman Code:"  
        AssociatedControlID="txtSalesman_Code"  
        Runat="server" />  
    <asp:TextBox  
        id="txtSalesman_Code"  
        Runat="server" />  
    <custom:AjaxValidator  
        id="AjaxValidator1"  
        ControlToValidate="txtSalesman_Code"  
        Text="User name already taken!"  
        OnServerValidate="AjaxValidator1_ServerValidate"  
        Runat="server" />  
 
    <br /><br />  
    <asp:Label  
        id="lblSalesman_LastName"  
        Text="Last Name:"  
        AssociatedControlID="txtSalesman_LastName"  
        Runat="server" />  
    <asp:TextBox  
        id="txtSalesman_LastName"  
        Runat="server" />  
 
    <br /><br />  
    <asp:Button  
        id="btnSubmit"  
        Text="Submit"  
        Runat="server" OnClick="btnSubmit_Click" />  
 
    </div>  
    </form>  
</body>  
</html>  
 
<%@ Page Language="VB" %>
<%@ Register TagPrefix="custom" Namespace="myControls" %>
<%@ Import Namespace="System.Data.SqlClient" %>
<%@ Import Namespace="System.Web.Configuration" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
 
 
    ''' Validation function that is called on both the client and server
 
    Protected Sub AjaxValidator1_ServerValidate(ByVal source As Object, ByVal args As ServerValidateEventArgs)
        If Salesman_CodeExists(args.Value) Then
            args.IsValid = False
        Else
            args.IsValid = True
            Me.btnSubmit.Attributes.Add("onclick", "alert('Please try a different Salesman Code!');return false;")
        End If
    End Sub
 
    ''' <summary>
    ''' Returns true when user name already exists
    ''' in Users database table
    ''' </summary>
    Private Function Salesman_CodeExists(ByVal Salesman_Code As String) As Boolean
        Dim conString As String = WebConfigurationManager.ConnectionStrings("PennerConnectionString").ConnectionString
        Dim con As New SqlConnection(conString)
        Dim cmd As New SqlCommand("SELECT COUNT(*) FROM tblSalesman WHERE Salesman_Code=@Salesman_Code", con)
        cmd.Parameters.AddWithValue("@Salesman_Code", Salesman_Code)
        Dim result As Boolean = False
        Using con
            con.Open()
            Dim count As Integer = CType(cmd.ExecuteScalar(), Integer)
            If count > 0 Then
                result = True
            Else
            End If
        End Using
        Return result
    End Function
 
 
    ''' Insert new user name to Users database table
 
    Protected Sub btnSubmit_Click(ByVal sender As Object, ByVal e As EventArgs)
        Dim conString As String = WebConfigurationManager.ConnectionStrings("PennerConnectionString").ConnectionString
        Dim con As New SqlConnection(conString)
        Dim cmd As New SqlCommand("INSERT tblSalesman (Salesman_Code,Salesman_LastName) VALUES (@Salesman_Code,@Salesman_LastName)", con)
        cmd.Parameters.AddWithValue("@Salesman_Code", txtSalesman_Code.Text)
        cmd.Parameters.AddWithValue("@Salesman_LastName", txtSalesman_LastName.Text)
        Using con
            con.Open()
            cmd.ExecuteNonQuery()
        End Using
        txtSalesman_Code.Text = String.Empty
        txtSalesman_LastName.Text = String.Empty
    End Sub
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>Show AjaxValidator</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
 
    <asp:Label
        id="lblSalesman_Code"
        Text="Salesman Code:"
        AssociatedControlID="txtSalesman_Code"
        Runat="server" />
    <asp:TextBox
        id="txtSalesman_Code"
        Runat="server" />
    <custom:AjaxValidator
        id="AjaxValidator1"
        ControlToValidate="txtSalesman_Code"
        Text="User name already taken!"
        OnServerValidate="AjaxValidator1_ServerValidate"
        Runat="server" />
 
    <br /><br />
    <asp:Label
        id="lblSalesman_LastName"
        Text="Last Name:"
        AssociatedControlID="txtSalesman_LastName"
        Runat="server" />
    <asp:TextBox
        id="txtSalesman_LastName"
        Runat="server" />
 
    <br /><br />
    <asp:Button
        id="btnSubmit"
        Text="Submit"
        Runat="server" OnClick="btnSubmit_Click" />
 
    </div>
    </form>
</body>
</html>
<%@ Page Language="VB" %>  
<%@ Register TagPrefix="custom" Namespace="myControls" %>  
<%@ Import Namespace="System.Data.SqlClient" %>  
<%@ Import Namespace="System.Web.Configuration" %>  
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"   
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">  
<script runat="server">  
  
  
    ''' Validation function that is called on both the client and server   
  
    Protected Sub AjaxValidator1_ServerValidate(ByVal source As Object, ByVal args As ServerValidateEventArgs)   
        If Salesman_CodeExists(args.Value) Then   
            args.IsValid = False  
        Else   
            args.IsValid = True  
            Me.btnSubmit.Attributes.Add("onclick", "alert('Please try a different Salesman Code!');return false;")   
        End If   
    End Sub   
  
    ''' <summary>  
    ''' Returns true when user name already exists   
    ''' in Users database table   
    ''' </summary>  
    Private Function Salesman_CodeExists(ByVal Salesman_Code As String) As Boolean   
        Dim conString As String = WebConfigurationManager.ConnectionStrings("PennerConnectionString").ConnectionString   
        Dim con As New SqlConnection(conString)   
        Dim cmd As New SqlCommand("SELECT COUNT(*) FROM tblSalesman WHERE Salesman_Code=@Salesman_Code", con)   
        cmd.Parameters.AddWithValue("@Salesman_Code", Salesman_Code)   
        Dim result As Boolean = False  
        Using con   
            con.Open()   
            Dim count As Integer = CType(cmd.ExecuteScalar(), Integer)   
            If count > 0 Then   
                result = True  
            Else   
            End If   
        End Using   
        Return result   
    End Function   
  
  
    ''' Insert new user name to Users database table   
  
    Protected Sub btnSubmit_Click(ByVal sender As Object, ByVal e As EventArgs)   
        Dim conString As String = WebConfigurationManager.ConnectionStrings("PennerConnectionString").ConnectionString   
        Dim con As New SqlConnection(conString)   
        Dim cmd As New SqlCommand("INSERT tblSalesman (Salesman_Code,Salesman_LastName) VALUES (@Salesman_Code,@Salesman_LastName)", con)   
        cmd.Parameters.AddWithValue("@Salesman_Code", txtSalesman_Code.Text)   
        cmd.Parameters.AddWithValue("@Salesman_LastName", txtSalesman_LastName.Text)   
        Using con   
            con.Open()   
            cmd.ExecuteNonQuery()   
        End Using   
        txtSalesman_Code.Text = String.Empty   
        txtSalesman_LastName.Text = String.Empty   
    End Sub   
</script>  
<html xmlns="http://www.w3.org/1999/xhtml" >  
<head id="Head1" runat="server">  
    <title>Show AjaxValidator</title>  
</head>  
<body>  
    <form id="form1" runat="server">  
    <div>  
  
    <asp:Label  
        id="lblSalesman_Code"  
        Text="Salesman Code:"  
        AssociatedControlID="txtSalesman_Code"  
        Runat="server" />  
    <asp:TextBox  
        id="txtSalesman_Code"  
        Runat="server" />  
    <custom:AjaxValidator  
        id="AjaxValidator1"  
        ControlToValidate="txtSalesman_Code"  
        Text="User name already taken!"  
        OnServerValidate="AjaxValidator1_ServerValidate"  
        Runat="server" />  
  
    <br /><br />  
    <asp:Label  
        id="lblSalesman_LastName"  
        Text="Last Name:"  
        AssociatedControlID="txtSalesman_LastName"  
        Runat="server" />  
    <asp:TextBox  
        id="txtSalesman_LastName"  
        Runat="server" />  
  
    <br /><br />  
    <asp:Button  
        id="btnSubmit"  
        Text="Submit"  
        Runat="server" OnClick="btnSubmit_Click" />  
  
    </div>  
    </form>  
</body>  
</html>  

<%@ Page Language="VB" %>
<%@ Register TagPrefix="custom" Namespace="myControls" %>
<%@ Import Namespace="System.Data.SqlClient" %>
<%@ Import Namespace="System.Web.Configuration" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">


    ''' Validation function that is called on both the client and server

    Protected Sub AjaxValidator1_ServerValidate(ByVal source As Object, ByVal args As ServerValidateEventArgs)
        If Salesman_CodeExists(args.Value) Then
            args.IsValid = False
        Else
            args.IsValid = True
            Me.btnSubmit.Attributes.Add("onclick", "alert('Please try a different Salesman Code!');return false;")
        End If
    End Sub

    ''' <summary>
    ''' Returns true when user name already exists
    ''' in Users database table
    ''' </summary>
    Private Function Salesman_CodeExists(ByVal Salesman_Code As String) As Boolean
        Dim conString As String = WebConfigurationManager.ConnectionStrings("PennerConnectionString").ConnectionString
        Dim con As New SqlConnection(conString)
        Dim cmd As New SqlCommand("SELECT COUNT(*) FROM tblSalesman WHERE Salesman_Code=@Salesman_Code", con)
        cmd.Parameters.AddWithValue("@Salesman_Code", Salesman_Code)
        Dim result As Boolean = False
        Using con
            con.Open()
            Dim count As Integer = CType(cmd.ExecuteScalar(), Integer)
            If count > 0 Then
                result = True
            Else
            End If
        End Using
        Return result
    End Function


    ''' Insert new user name to Users database table

    Protected Sub btnSubmit_Click(ByVal sender As Object, ByVal e As EventArgs)
        Dim conString As String = WebConfigurationManager.ConnectionStrings("PennerConnectionString").ConnectionString
        Dim con As New SqlConnection(conString)
        Dim cmd As New SqlCommand("INSERT tblSalesman (Salesman_Code,Salesman_LastName) VALUES (@Salesman_Code,@Salesman_LastName)", con)
        cmd.Parameters.AddWithValue("@Salesman_Code", txtSalesman_Code.Text)
        cmd.Parameters.AddWithValue("@Salesman_LastName", txtSalesman_LastName.Text)
        Using con
            con.Open()
            cmd.ExecuteNonQuery()
        End Using
        txtSalesman_Code.Text = String.Empty
        txtSalesman_LastName.Text = String.Empty
    End Sub
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
    <title>Show AjaxValidator</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>

    <asp:Label
        id="lblSalesman_Code"
        Text="Salesman Code:"
        AssociatedControlID="txtSalesman_Code"
        Runat="server" />
    <asp:TextBox
        id="txtSalesman_Code"
        Runat="server" />
    <custom:AjaxValidator
        id="AjaxValidator1"
        ControlToValidate="txtSalesman_Code"
        Text="User name already taken!"
        OnServerValidate="AjaxValidator1_ServerValidate"
        Runat="server" />

    <br /><br />
    <asp:Label
        id="lblSalesman_LastName"
        Text="Last Name:"
        AssociatedControlID="txtSalesman_LastName"
        Runat="server" />
    <asp:TextBox
        id="txtSalesman_LastName"
        Runat="server" />

    <br /><br />
    <asp:Button
        id="btnSubmit"
        Text="Submit"
        Runat="server" OnClick="btnSubmit_Click" />

    </div>
    </form>
</body>
</html>

Below is my AjaxValidator.vb file:

ASP.NET Syntax (Toggle Plain Text)
Imports System   
Imports System.Web   
Imports System.Web.UI   
Imports System.Web.UI.WebControls   
 
Namespace myControls   
 
    ''' <summary>   
    ''' Enables you to perform custom validation on both the client and server   
    ''' </summary>   
    Public Class AjaxValidator   
        Inherits BaseValidator   
        Implements ICallbackEventHandler   
 
        Public Event ServerValidate As ServerValidateEventHandler   
 
        Dim _controlToValidateValue As String  
 
        Protected Overrides Sub OnPreRender(ByVal e As EventArgs)   
            Dim eventRef As String = Page.ClientScript.GetCallbackEventReference(Me, "", "", "")   
 
            ' Register include file   
            Dim includeScript As String = Page.ResolveClientUrl("~/js/AjaxValidator.js")   
            Page.ClientScript.RegisterClientScriptInclude("AjaxValidator", includeScript)   
 
            ' Register startup script   
            Dim startupScript As String = String.Format("document.getElementById('{0}').evaluationfunction = 'AjaxValidatorEvaluateIsValid'", Me.ClientID)   
            Page.ClientScript.RegisterStartupScript(Me.GetType(), "AjaxValidator", startupScript, True)   
 
            MyBase.OnPreRender(e)   
        End Sub  
 
        ''' <summary>   
        ''' Only do the AJAX call on browsers that support it   
        ''' </summary>   
        Protected Overrides Function DetermineRenderUplevel() As Boolean  
            Return Context.Request.Browser.SupportsCallback   
        End Function  
 
        ''' <summary>   
        ''' Server method called by client AJAX call   
        ''' </summary>   
        Public Function GetCallbackResult() As String Implements ICallbackEventHandler.GetCallbackResult   
            Return ExecuteValidationFunction(_controlToValidateValue).ToString()   
        End Function  
 
        ''' <summary>   
        ''' Return callback result to client   
        ''' </summary>   
        Public Sub RaiseCallbackEvent(ByVal eventArgument As String) Implements ICallbackEventHandler.RaiseCallbackEvent   
            _controlToValidateValue = eventArgument   
        End Sub  
 
        ''' <summary>   
        ''' Server-side method for validation   
        ''' </summary>   
        Protected Overrides Function EvaluateIsValid() As Boolean  
            Dim controlToValidateValue As String = Me.GetControlValidationValue(Me.ControlToValidate)   
            Return ExecuteValidationFunction(controlToValidateValue)   
        End Function  
 
        ''' <summary>   
        ''' Performs the validation for both server and client   
        ''' </summary>   
        Private Function ExecuteValidationFunction(ByVal controlToValidateValue As String) As Boolean  
            Dim args As New ServerValidateEventArgs(controlToValidateValue, Me.IsValid)   
            RaiseEvent ServerValidate(Me, args)   
            Return args.IsValid   
        End Function  
 
    End Class  
 
End Namespace
Imports System   
Imports System.Web   
Imports System.Web.UI   
Imports System.Web.UI.WebControls   
  
Namespace myControls   
  
    ''' <summary>   
    ''' Enables you to perform custom validation on both the client and server   
    ''' </summary>   
    Public Class AjaxValidator   
        Inherits BaseValidator   
        Implements ICallbackEventHandler   
  
        Public Event ServerValidate As ServerValidateEventHandler   
  
        Dim _controlToValidateValue As String  
  
        Protected Overrides Sub OnPreRender(ByVal e As EventArgs)   
            Dim eventRef As String = Page.ClientScript.GetCallbackEventReference(Me, "", "", "")   
  
            ' Register include file   
            Dim includeScript As String = Page.ResolveClientUrl("~/js/AjaxValidator.js")   
            Page.ClientScript.RegisterClientScriptInclude("AjaxValidator", includeScript)   
  
            ' Register startup script   
            Dim startupScript As String = String.Format("document.getElementById('{0}').evaluationfunction = 'AjaxValidatorEvaluateIsValid'", Me.ClientID)   
            Page.ClientScript.RegisterStartupScript(Me.GetType(), "AjaxValidator", startupScript, True)   
  
            MyBase.OnPreRender(e)   
        End Sub  
  
        ''' <summary>   
        ''' Only do the AJAX call on browsers that support it   
        ''' </summary>   
        Protected Overrides Function DetermineRenderUplevel() As Boolean  
            Return Context.Request.Browser.SupportsCallback   
        End Function  
  
        ''' <summary>   
        ''' Server method called by client AJAX call   
        ''' </summary>   
        Public Function GetCallbackResult() As String Implements ICallbackEventHandler.GetCallbackResult   
            Return ExecuteValidationFunction(_controlToValidateValue).ToString()   
        End Function  
  
        ''' <summary>   
        ''' Return callback result to client   
        ''' </summary>   
        Public Sub RaiseCallbackEvent(ByVal eventArgument As String) Implements ICallbackEventHandler.RaiseCallbackEvent   
            _controlToValidateValue = eventArgument   
        End Sub  
  
        ''' <summary>   
        ''' Server-side method for validation   
        ''' </summary>   
        Protected Overrides Function EvaluateIsValid() As Boolean  
            Dim controlToValidateValue As String = Me.GetControlValidationValue(Me.ControlToValidate)   
            Return ExecuteValidationFunction(controlToValidateValue)   
        End Function  
  
        ''' <summary>   
        ''' Performs the validation for both server and client   
        ''' </summary>   
        Private Function ExecuteValidationFunction(ByVal controlToValidateValue As String) As Boolean  
            Dim args As New ServerValidateEventArgs(controlToValidateValue, Me.IsValid)   
            RaiseEvent ServerValidate(Me, args)   
            Return args.IsValid   
        End Function  
  
    End Class  
  
End Namespace

Below is my AjaxValidator.js file:

ASP.NET Syntax (Toggle Plain Text)
// Performs AJAX call back to server   
function AjaxValidatorEvaluateIsValid(val) {   
    var value = ValidatorGetValue(val.controltovalidate);   
    WebForm_DoCallback(val.id, value, AjaxValidatorResult, val,   
AjaxValidatorError, true);   
    return true;   
}   
 
// Called when result is returned from server   
function AjaxValidatorResult(returnValue, context) {   
    if (returnValue == 'True')   
        context.isvalid = true;   
    else   
        context.isvalid = false;   
    ValidatorUpdateDisplay(context);   
}   
 
// If there is an error, show it   
function AjaxValidatorError(message) {   
    alert('Error: ' + message);    
}
// Performs AJAX call back to server   
function AjaxValidatorEvaluateIsValid(val) {   
    var value = ValidatorGetValue(val.controltovalidate);   
    WebForm_DoCallback(val.id, value, AjaxValidatorResult, val,   
AjaxValidatorError, true);   
    return true;   
}   
  
// Called when result is returned from server   
function AjaxValidatorResult(returnValue, context) {   
    if (returnValue == 'True')   
        context.isvalid = true;   
    else   
        context.isvalid = false;   
    ValidatorUpdateDisplay(context);   
}   
  
// If there is an error, show it   
function AjaxValidatorError(message) {   
    alert('Error: ' + message);    
}

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