(C# ASP.NET Core) Serializing DateTime into Session

What's the problem about?

We want to store a DateTime in Session, but ASP.NET Core has a direct support only for Int32 and String type of data; there is no built-in method that allows us to save a DateTime type.

What's the solution?

The technique is to serialize a DateTime instance to a json string, and store that string in the session instead. And, deserialize it for retrieval.

The following utility extension methods on ISession are recommended by the ASP.NET Core team.

using Microsoft.AspNetCore.Http;

using System.Text.Json;

// we wrote it in a folder called 
// "Utilities" directly in the root 
// of the project directory 
namespace MySession.Utilities
{

  public static class SessionExtensions
  {

    // extension method on ISession 
    // how to use: HttpContext.Session.Set<T>(key, value) 
    public static void Set<T>(this ISession session, string key, T value)
    {

      session.SetString(key, JsonSerializer.Serialize(value));

    }

    // extension method on ISession 
    // how to use: HttpContext.Session.Get<T>(key) 
    public static T Get<T>(this ISession session, string key)
    {

      var value = session.GetString(key);

      return value == null ? default : JsonSerializer.Deserialize<T>(value);

    }

  }

}

Video Explanation with a Working Example

Please watch the following youtube video:

Objective of this Walkthrough

There is only one razor page in this project. The page is called Index.

When a user starts his session, the system time is saved in a session variable. On subsequent requests/refreshes of the page, this start time is read from the session and shown to him as the start time of his browsing session.

Step 1 of 4: Configure the use of Session

Configure the use of session as explained in the tutorial (C# ASP.NET Core) How to use Session for State Management

Step 2 of 4: Add the Session Extensions

Create any folder, say, Utility and paste the above utility class there, so that we have the Set<T> and Get<T> extension methods.

Step 3 of 4: Complete the Index.cshtml.cs file

Complete the backing class as shown below.

using Microsoft.AspNetCore.Http;

using Microsoft.AspNetCore.Mvc.RazorPages;

using MySession.Utilities;

using System;

using System.ComponentModel.DataAnnotations;

namespace MySession.Pages
{

  public class IndexModel : PageModel
  {

    // a string for the session key 
    // this will prevent bugs due to 
    // bad typing 
    internal const string SESS_START = "SKEY_STIME";

    // start time of this session 
    // apply format 4:35:02 PM 27-Aug-2021 
    [DisplayFormat(DataFormatString = @"{0:h\:mm\:ss tt dd-MMM-yyyy}")]
    public DateTime StartTime { get; private set; }

    // when the index page is requested 
    public void OnGet()
    {

      // read the stored datetime 
      StartTime = HttpContext.Session.Get<DateTime>(SESS_START);

      // if empty, i.e, default (i.e., DateTime.UnspecifiedKind) 
      if (StartTime == default)
      {

        StartTime = DateTime.Now;

        // store the current time 
        HttpContext.Session.Set<DateTime>(SESS_START, StartTime);

      }

    }

  }

}

Step 4 of 4: Complete the Index.cshtml Razor file

Complete the razor mark-up file as shown below.

@page

@model MySession.Pages.IndexModel

@if (Model.StartTime != default)
{
  <div>

    This session started:

    @Html.DisplayFor(x => Model.StartTime)

  </div>
}