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Session State in ASP.NET Core, .NET 5

Neil Taylor -

This article describes some key steps needed to make use of Session state  on the ASP.NET Core platform.

Microsoft has a good article on Session and state management in ASP.NET Core. The Microsoft article covers wider issues beyond Session state and is a useful article to read.

Namespace

To access the Session data in your code, you will need to use the following namespace.

using Microsoft.AspNetCore.Http;

Storing data

The SessionExtensions class provides methods to store String and Int32. 

// Storing a string
string someValue = "a value to store in session data";
HttpContext.Session.SetString("SomeKeyForString", someValue);

// Storing an int
int pageNumber = 10
HttpContext.Session.SetInt32("SomeKeyForInt", pageNumber);

There must be data that you are trying to store. If you pass a null value, there will be a build-time error.

If you want to store a complex type, such as your own object, then you will need to specifiy how that should be serialized. An article from Ben Cull provides an example for a JSON object, as part of a page with more details on Session Data in ASP.NET MVC.

Clearing the data

To clear the data, use the Remove method from ISession.

HttpContext.Session.Remove("SomeKey");

Setup

In order to access HttpContext in a Controller, there is a little setup. The following is a summary from the Session state part of the Microsoft article.

In ConfigureServices, add the following code as a starting point. This sets up the app to store Session data in memory on the machine that is running the application and it sets a default timeout for 30 minutes. 

services.AddDistributedMemoryCache();

services.AddSession(options =>
{
    options.IdleTimeout = TimeSpan.FromMinutes(30);
});

Also, in the Configure method, add the following. I put it after app.UseAuthentication() and app.UseAuthorisation() setup and before app.UseEndpoints(). 

app.UseSession();

There are other ways to setup the options for Session data. See the Session options section of the Microsoft article for links to what you can configure.

Accessing State in a Razor view

If you want to access the Session data in a RazorView, e.g. Index.cshtml, you need to do a little setup.

Firstly, configure access to the HttpContextAccessor.  In Startup.cs, add the following to the ConfigureServices method. 

services.AddHttpContextAccessor();

Then, in the view, include the following at the top of the view. 

@using Microsoft.AspNetCore.Http
@inject Microsoft.AspNetCore.Http.IHttpContextAccessor HttpContextAccessor

Finally, within the view, use the following to access a value:

<p>
Example data: 
@HttpContextAccessor.HttpContext.Session.GetString("SomeKeyForString")
</p>

Microsoft has an article about how to access HttpContext ASP.NET Core, which covers some other situations if you need access to HttpContext.