In this article I will explain with an example, how to implement jQuery AutoComplete DropDown (ComboBox) in ASP.Net MVC 5 Razor.
The jQuery AutoComplete plugin is actually applied to a TextBox but it can be made to work as a DropDown (ComboBox) by populating the AutoComplete results on TextBox focus as well as when User types in some Text.
The data for the jQuery AutoComplete DropDown (ComboBox) will be populated from database using Entity Framework in ASP.Net MVC Razor.
Note: For beginners in ASP.Net MVC, please refer my article ASP.Net MVC Hello World Tutorial with Sample Program example.
 
 
Database
Here I am making use of Microsoft’s Northwind Database. You can download it from here.
 
 

Creating an Entity Data Model
The very first step is to create an ASP.Net MVC Application and connect it to the Northwind Database using Entity Framework.
Note: For more details please refer my article ASP.Net MVC: Simple Entity Framework Tutorial with example.
 
Following is the Entity Data Model of the Customers Table of the Northwind Database which will be used later in this project.
Implement jQuery AutoComplete DropDown (ComboBox) in ASP.Net MVC
 
 
Controller
The Controller consists of three Action methods.
Action method for handling GET operation
Inside this Action method, simply the View is returned.
 
Action method for handling the jQuery AutoComplete
This Action method accepts a parameter named “prefix”. When this method is accessed by the jQuery AutoComplete plugin, the records of the Customers Table of the Northwind database are fetched using the Entity Framework.
The fetched records are then filtered and returned back to the View as JSON.
 
Action method for handling POST operation
This Action method handles the Form submission and displays the Customer Name and CustomerId of the selected item in jQuery AutoComplete using ViewBag object.
Note: For more details on displaying message from Controller to View, please refer my article Display (Pass) String Message from Controller to View in ASP.Net MVC.
 
public class HomeController : Controller
{
    // GET: Home
    public ActionResult Index()
    {
        return View();
    }
 
    [HttpPost]
    public JsonResult AutoComplete(string prefix)
    {
        NorthwindEntities entities = new NorthwindEntities();
        var customers = (from customer in entities.Customers
                         where customer.ContactName.StartsWith(prefix)
                         select new
                         {
                             label = customer.ContactName,
                             val = customer.CustomerID
                         }).ToList();
 
        return Json(customers);
    }
 
    [HttpPost]
    public ActionResult Index(string CustomerName, string CustomerId)
    {
        ViewBag.Message = "CustomerName: " + CustomerName + " CustomerId: " + CustomerId;
        return View();
    }
}
 
 
View
The View consists of an HTML Form which has been created using the Html.BeginForm method with the following parameters.
ActionName – Name of the Action. In this case the name is Index.
ControllerName – Name of the Controller. In this case the name is Home.
FormMethod – It specifies the Form Method i.e. GET or POST. In this case it will be set to POST.
The Form consists of three elements i.e. a TextBox (implemented as AutoComplete DropDown or ComboBox), a Hidden Field (for saving the Value part of the Autocomplete Item) and a Submit Button.
The jQuery AutoComplete plugin has been applied to the TextBox and the URL of the plugin is set to the AutoComplete Action method.
The jQuery AutoComplete plugin will be made to work as a DropDown (ComboBox) i.e. displaying all records in database when the AutoComplete TextBox is clicked.
This is done by setting the minLength property of the jQuery AutoComplete plugin to 0 and forcing the jQuery AutoComplete plugin to perform a Search when the TextBox is focused.
@{
    Layout = null;
}
 
<!DOCTYPE html>
 
<html>
<head>
    <meta name="viewport" content="width=device-width"/>
    <title>Index</title>
    <style type="text/css">
        body
        {
            font-family: Arial;
            font-size: 10pt;
        }
 
        .ui-autocomplete
        {
            overflow:auto;
            max-height:100px;
        }
    </style>
</head>
<body>
    <script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.10.0.min.js" type="text/javascript"></script>
    <script src="https://ajax.aspnetcdn.com/ajax/jquery.ui/1.9.2/jquery-ui.min.js" type="text/javascript"></script>
    <link href="https://ajax.aspnetcdn.com/ajax/jquery.ui/1.9.2/themes/blitzer/jquery-ui.css"
          rel="Stylesheet" type="text/css"/>
    <script type="text/javascript">
        $(function () {
            $("#txtCustomer").autocomplete({
                source: function (request, response) {
                    $.ajax({
                        url: '/Home/AutoComplete/',
                        data: "{ 'prefix': '" + request.term + "'}",
                        dataType: "json",
                        type: "POST",
                        contentType: "application/json; charset=utf-8",
                        success: function (data) {
                            response($.map(data, function (item) {
                                return item;
                            }))
                        },
                        error: function (response) {
                            alert(response.responseText);
                        },
                        failure: function (response) {
                            alert(response.responseText);
                        }
                    });
                },
                select: function (e, i) {
                    $("#hfCustomer").val(i.item.val);
                },
                minLength: 0
            }).focus(function () {
                $(this).autocomplete("search");
            });
        });
    </script>
    @using (Html.BeginForm("Index", "Home", FormMethod.Post))
    {
        <input type="text" id="txtCustomer" name="CustomerName"/>
        <input type="hidden" id="hfCustomer" name="CustomerId"/>
        <br/><br/>
        <input type="submit" id="btnSubmit" value="Submit"/>
        <br/><br/>
        @ViewBag.Message
    }
</body>
</html>
 
 
Screenshot
Implement jQuery AutoComplete DropDown (ComboBox) in ASP.Net MVC
 
 
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