Instant Username check availablity with database using asp.net - asp.net

Question

I am trying to use one of the best example for checking the username availability from the below site
http://www.highoncoding.com/Articles/439_Performing_Instant_UserName_Availability_Check_Using_JQuery_Ajax_API.aspx
And It's just verifying with some pre-initiated names but I wan't to try with my database can anyone suggest me how to proceed further.
Here is the code:
<script language="javascript" type="text/javascript">
var userName = '';
$(document).ready(function()
{
$("#txtUserName").blur(function()
{
userName = $(this).val();
if(userName.length <= 6)
{
$("#display").text("username must be atleast 7 characters");
$("#display").css("background-color","red");
}
else
{
$.ajax(
{
type:"POST",
url:"AjaxService.asmx/CheckUserNameAvailability",
data:"{\"userName\":\"" + userName + "\"}",
dataType:"json",
contentType:"application/json",
success: function(response)
{
if(response.d == true)
{
$("#display").text("username is available");
$("#display").css("background-color","lightgreen");
}
else
{
$("#display").text("username is already taken");
$("#display").css("background-color","red");
}
}
});
}
});
});
</script>
This AjaxService.asmx:
Imports System.Collections
Imports System.ComponentModel
Imports System.Data
Imports System.Linq
Imports System.Web
Imports System.Web.Services
Imports System.Web.Services.Protocols
Imports System.Xml.Linq
Imports System.Collections.Generic
Namespace JQueryUserNameAvailability
<WebService([Namespace] := "http://tempuri.org/")> _
<WebServiceBinding(ConformsTo := WsiProfiles.BasicProfile1_1)> _
<ToolboxItem(False)> _
<System.Web.Script.Services.ScriptService> _
Public Class AjaxService
Inherits System.Web.Services.WebService
<WebMethod> _
Public Function CheckUserNameAvailability(userName As String) As Boolean
Dim userNames As List(Of [String]) = New List(Of String)() From { _
"azamsharp", _
"johndoe", _
"marykate", _
"alexlowe", _
"scottgu" _
}
Dim user = (From u In userNames Where u.ToLower().Equals(userName.ToLower())u).SingleOrDefault(Of [String])()
Return If([String].IsNullOrEmpty(user), True, False)
End Function
End Class
End Namespace
Modified code:
Public Function CheckUserNameAvailability(ByVal userName As String) As Boolean
Dim strSql As String = String.Format("SELECT COUNT(UserNameCol) FROM Registration WHERE UserNameCol = '{0}'", userName)
Dim strConnection As String = "Data Source=.\sqlexpress;Initial Catalog=Users;Integrated Security=True"
Dim sqlConn As New SqlConnection(strConnection)
Dim sqlDataAdap As New SqlDataAdapter(strSql, sqlConn)
Dim dt As New DataTable()
sqlDataAdap.Fill(dt)
If Convert.ToInt32(dt.Rows(0)(0)) > 0 Then
Return False
End If
Return True
End Function

Answer 1

Modify your CheckUserNameAvailability function to get data from the table where you have saved all the username. An example:
Public Function CheckUserNameAvailability(userName As String) As Boolean
Dim strSql as String = String.Format("SELECT COUNT(userNameCol) FROM users WHERE userNameCol = '{0}'", userName)
Dim sqlConn as new SqlConnection(SQL Connection String)
Dim sqlDataAdap as new SqlDataAdapter(strSql, sqlConn)
Dim dt as new DataTable()
sqlDataAdap.Fill(dt)
If Convert.ToInt32(dt.Rows(0)(0)) > 0 Then
Return false
End If
Return true
End Function