In this article I will explain with an example, how to implement multiple Selection DropDownList using jQuery Select2 plugin in ASP.Net Core Razor Pages.
The multiple Selection DropDownList will be populated from SQL Server database using Entity Framework in ASP.Net Core Razor Pages.
 
 
jQuery Plugin for Multiple Selection DropDownList
This article makes use of Select2 jQuery Plugin for implementing multiple Selection DropDownList in ASP.Net Core Razor Pages.
 
 
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 Razor Pages: Multiple Selection DropDownList using jQuery Select2 plugin
 
I have already inserted few records in the table.
ASP.Net Core Razor Pages: Multiple Selection DropDownList using jQuery Select2 plugin
 
Note: You can download the database table SQL by clicking the download link below.
          Download SQL file
 
 

Namespaces
You will need to import the following namespace.
using Microsoft.AspNetCore.Mvc.Rendering;
 
 
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 Microsoft.EntityFrameworkCore;
using Razor_MultiSelect_DDL_jQuery.Models;
 
namespace Razor_MultiSelect_DDL_jQuery
{
    public class DBCtx : DbContext
    {
        public DBCtx(DbContextOptions<DBCtx> options) : base(options)
        {
        }
 
        public DbSet<Customer> Customers { get; set; }
    }
}
 
 
Razor PageModel (Code-Behind)
The PageModel consists of two Action Handler methods.
Handler method for handling GET operation
Inside this Handler method, the records are fetched from the Customers table using Entity Framework and are copied to SelectList class object and assigned to the public property Customers, which is used for populating DropDownList in ASP.Net Core Razor Pages.
 
Handler method for handling Button Click and POST operation
This Handler method handles the POST call when the Submit Button is clicked and the Form is submitted.
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 ViewData 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 Core Razor Pages: Display JavaScript Alert Message Box.
 
public class IndexModel : PageModel
{
    private DBCtx Context { get; }
    public IndexModel(DBCtx _context)
    {
        this.Context = _context;
    }
 
    public SelectList Customers { get; set; }
 
    public void OnGet()
    {
        this.Customers = new SelectList(this.Context.Customers, "CustomerId", "Name");
    }
 
    public void OnPostSubmit(string[] customerIds)
    {
        this.Customers = new SelectList(this.Context.Customers, "CustomerId", "Name");
        string message = "";
        foreach (string customerId in customerIds)
        {
            SelectListItem selectedItem = this.Customers.ToList().Find(p => p.Value == customerId);
            message += "Name: " + selectedItem.Text;
            message += "\\nID: " + selectedItem.Value;
            message += "\\n";
        }
        ViewData["Message"] = message;
    }
}
 
 
Razor Page (HTML)
Form
The HTML of Razor Page consists of an HTML Form with a DropDownList and a Submit Button.
The Submit Button has been set with the POST Handler method using the asp-page-handler attribute.
Note: In the Razor PageModel, the Handler method name is OnPostSubmit but here it will be specified as Submit when calling from the Razor HTML Page.
 
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 multiple selected CustomerId values are sent to the Razor PageModel.
Finally, the ViewData object returned from the PageModel is checked for NULL and if it is not NULL then the Name and ID values of the multiple selected Customers are displayed using JavaScript Alert MessageBox.
 
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.
@page
@addTagHelper*, Microsoft.AspNetCore.Mvc.TagHelpers
@model Razor_MultiSelect_DDL_jQuery.Pages.IndexModel
 
@{
    Layout = null;
}
 
<!DOCTYPE html>
 
<html>
<head>
    <meta name="viewport" content="width=device-width"/>
    <title>Index</title>
</head>
<body>
    <form method="post">
        <select id="ddlCustomers" name="CustomerIds" asp-items="@Model.Customers" multiple="multiple">
            <option value="0">--Select Customer--</option>
        </select>
        <br/>
        <br/>
        <input type="submit" value="Submit" asp-page-handler="Submit"/>
        @if (ViewData["Message"] != null)
        {
            <script type="text/javascript">
                window.onload = function () {
                    alert("@ViewData["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 Razor Pages: Multiple Selection DropDownList using jQuery Select2 plugin
 
 
Downloads