jQuery Autocomplete in an C# Environment with Database

first example:

ASPX - uses codebehind

<script src="js/jquery-1.8.3.js" type="text/javascript"></script>
	<script type="text/javascript" src="js/jquery-ui-1.9.2.custom.min.js"></script>
	<link rel="stylesheet" type="text/css" href="css/jquery-ui.css" />
	<script type="text/javascript">

	$(function() {
		var availableTags = [ <%= SuggestionList %> ];

		$( "#<%= TextBox1.ClientID %>" ).autocomplete({
			source: availableTags
		});
	});

	</script>

page body

	<form id="form1" runat="server">
	<div>
		<div class="ui-widget">
			<label for="TextBox1">
				Tags:
			</label>
			<asp:TextBox ID="TextBox1" runat="server" />
		</div>
	</div>
	</form>

ASPX codebehind

public string SuggestionList = "";

protected void Page_Load(object sender, EventArgs e) {

	string queryString = "SELECT * FROM Customers  ORDER BY CompanyName";

	using (SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].ConnectionString)) {

		using (SqlCommand command = new SqlCommand(queryString, connection)) {

			connection.Open();

			using (SqlDataReader reader = command.ExecuteReader()) {

				while (reader.Read()) {

					if (string.IsNullOrEmpty(SuggestionList)) {
						SuggestionList += "\"" + reader["CompanyName"].ToString() + "\"";
					} else {
						SuggestionList += ", \"" + reader["CompanyName"].ToString() + "\"";
					}

				}
			}
		}
	}

}

second example:

ASPX - uses webservice

	<script src="js/jquery-1.8.3.js" type="text/javascript"></script>
	<script src="js/jquery-ui-1.9.2.custom.min.js" type="text/javascript"></script>
	<link href="css/jquery-ui.css" rel="stylesheet" type="text/css" />
	<asp:PlaceHolder runat="server" id="phSearchText">
		<script type="text/javascript">
			$(document).ready(function () {

				SearchText();

				function SearchText() {
					$("#<%=TextBox1.ClientID %>").autocomplete({
						source: function (request, response) {
							$.ajax({
								url: "EmployeeList.asmx/GetAutoCompleteData",
								type: "POST",
								dataType: "json",
								contentType: "application/json; charset=utf-8",
								data: "{ 'txt' : '" + $("#<%=TextBox1.ClientID %>").val() + "'}",
								dataFilter: function (data) { return data; },
								success: function (data) {
									response($.map(data.d, function (item) {
										return {
											label: item,
											value: item
										}
									}))
									//debugger;
								},
								error: function (result) {
									alert("Error");
								}
							});
						},
						minLength: 1,
						delay: 1000
					});
				}
			});
		</script>
	</asp:PlaceHolder>

page body

	<form id="form1" runat="server">
	<div class="ui-widget">
		<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
	</div>
	</form>

WebService, this happens to use ADO.Net, but you could use pretty much anything as a valid query source

[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[System.ComponentModel.ToolboxItem(false)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
[System.Web.Script.Services.ScriptService]
public class EmployeeList : System.Web.Services.WebService
{

	[WebMethod]
	[ScriptMethod(ResponseFormat = ResponseFormat.Json)]
	public List<string> GetAutoCompleteData(string txt)
	{
		// your code to query the database goes here
		List<string> result = new List<string>();
		string QueryString = System.Configuration.ConfigurationManager.ConnectionStrings["NorthwindConnectionString"].ToString();

		using (SqlConnection obj_SqlConnection = new SqlConnection(QueryString))
		{
			using (SqlCommand obj_Sqlcommand = new SqlCommand("Select DISTINCT CompanyName as txt from Customers where CompanyName like @SearchText +'%' ", obj_SqlConnection))
			{
				obj_SqlConnection.Open();
				obj_Sqlcommand.Parameters.AddWithValue("@SearchText", txt);
				SqlDataReader obj_result = obj_Sqlcommand.ExecuteReader();
				while (obj_result.Read())
				{
					result.Add(obj_result["txt"].ToString().TrimEnd());
				}
			}
		}

		return result;
	}

}