In this article I will explain with an example, how to implement multiple Selection DropDownList using jQuery Select2 plugin in ASP.Net Core MVC.
The multiple Selection DropDownList will be populated from SQL Server database using Entity Framework in ASP.Net Core MVC.
 
 
jQuery Plugin for Multiple Selection DropDownList
This article makes use of Select2 jQuery Plugin for implementing multiple Selection DropDownList in ASP.Net Core MVC.
 
 
Database
I have made use of the following table Customers with the schema as follows. CustomerId is an Auto-Increment (Identity) column.
ASP.Net Core MVC: Multiple Selection DropDownList using jQuery Select2 plugin
 
I have already inserted few records in the table.
ASP.Net Core MVC: Multiple Selection DropDownList using jQuery Select2 plugin
 
Note: You can download the database table SQL by clicking the download link below.
          Download SQL file
 
 
Model
The Model class consists of the following two properties.
Note: In this article, only two Columns will be used and hence two properties are added to the class.
 
public class Customer
{
    public int CustomerId { get; set; }
    public string Name { get; set; }
}
 
 
Database Context
Once the Entity Framework is configured and connected to the database table, the Database Context will look as shown below.
Note: For beginners in ASP.Net Core and Entity Framework, please refer my ASP.Net Core: Simple Entity Framework Tutorial with example. It covers all the information needed for connecting and configuring Entity Framework with ASP.Net Core.
 
using MultiSelect_DropDown_jQuery_MVC_Core.Models;
using Microsoft.EntityFrameworkCore;
 
namespace MultiSelect_DropDown_jQuery_MVC_Core
{
    public class DBCtx : DbContext
    {
        public DBCtx(DbContextOptions<DBCtx> options) : base(options)
        {
        }
 
        public DbSet<Customer> Customers { get; set; }
    }
}
 
 
Controller
The Controller consists of the following two Action methods.
Action method for handling GET operation
Inside this Action method, the records are fetched from the Customers table using Entity Framework and are copied to SelectList class object which is used for populating DropDownList in .Net Core.
Finally, the SelectList class object is sent to the View.
 
Action method for handling POST operation
This Action method handles the call made from the POST function from the View.
When the Form is submitted, the posted multiple values are captured through the customerIds parameter which is also set as the Name of the DropDownList.
Then using a FOR EACH loop all the selected Customers are fetched using Lambda expression.
Finally, the Name and ID values of the selected Customers are set into a ViewBag object which will be later displayed in View using JavaScript Alert Message Box.
Note: For more details on displaying message using JavaScript Alert MessageBox, please refer my article ASP.Net MVC Core: Display Message from Controller in View using JavaScript Alert MessageBox.
 
public class HomeController : Controller
{
    private DBCtx Context { get; }
    public HomeController(DBCtx _context)
    {
        this.Context = _context;
    }
 
    public IActionResult Index()
    {
        SelectList customers = new SelectList(this.Context.Customers.ToList(), "CustomerId", "Name");
        return View(customers);
    }
 
    [HttpPost]
    public IActionResult Index(string[] customerIds)
    {
        SelectList customers = new SelectList(this.Context.Customers.ToList(), "CustomerId", "Name");
        ViewBag.Message = "";
        foreach (string customerId in customerIds)
        {
            SelectListItem selectedItem = customers.ToList().Find(p => p.Value == customerId);
            ViewBag.Message += "Name: " + selectedItem.Text;
            ViewBag.Message += "\\nID: " + selectedItem.Value;
            ViewBag.Message += "\\n";
        }
        return View(customers);
    }
}
 
 
View
Inside the View, in the very first line SelectList class is declared as Model for the View.
Form
The View consists of an HTML Form with following ASP.Net Tag Helpers attributes.
asp-action – Name of the Action. In this case the name is Index.
asp-controller – Name of the Controller. In this case the name is Home.
method – It specifies the Form Method i.e. GET or POST. In this case it will be set to POST.
The Form consists of a DropDownList, a Submit Button.
 
DropDownList
The Model data has been assigned to the DropDownList using the asp-items Tag Helpers attribute.
The multiple attribute of the DropDownList is set which enables multiple selections.
 
Form Submission
When the Submit Button is clicked, the Form gets submitted and the multiple selected CustomerId values are sent to the Controller.
Finally, the Name and ID values of the multiple selected Customers are displayed using JavaScript Alert Message Box.
 
Select2 jQuery Plugin implementation
First, the jQuery and the JS and CSS files of the jQuery Select2 plugin are inherited.
Then inside the jQuery document.ready event handler, the jQuery Select2 plugin is applied to the DropDownList.
@addTagHelper*, Microsoft.AspNetCore.Mvc.TagHelpers
@model SelectList
@{
    Layout = null;
}
 
<!DOCTYPE html>
 
<html>
<head>
    <meta name="viewport" content="width=device-width"/>
    <title>Index</title>
</head>
<body>
    <form method="post" asp-controller="Home" asp-action="Index">
        <select id="ddlCustomers" name="CustomerIds" asp-items="Model" multiple="multiple">
            <option value="0">--Select Customer--</option>
        </select>
        <br/>
        <br/>
        <input type="submit" value="Submit"/>
        @if (ViewBag.Message != null)
        {
            <script type="text/javascript">
                window.onload = function () {
                    alert("@ViewBag.Message");
                };
            </script>
        }
        <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/select2@4.0.13/dist/css/select2.min.css"/>
        <script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
        <script type="text/javascript" src="https://cdn.jsdelivr.net/npm/select2@4.0.13/dist/js/select2.min.js"></script>
        <script type="text/javascript">
            $(function () {
                $("#ddlCustomers").select2();
            });
        </script>
    </form>
</body>
</html>
 
 
Screenshot
ASP.Net Core MVC: Multiple Selection DropDownList using jQuery Select2 plugin
 
 
Downloads
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