How to Set and Retrieve Session Variables in .NET

Session variables play a crucial role in preserving user data across multiple requests on the server. They enable the server to track client interaction and state. This blog post will guide you on how to set and retrieve session variables in a C# API controller using Dependency Injection and the IHttpContextAccessor class.

1. Setting up the Startup.cs

Before we delve into setting and retrieving session variables, let’s configure our Startup.cs file to support session state.

public void ConfigureServices(IServiceCollection services)
{
    services.AddSession();
    services.AddSingleton<IHttpContextAccessor, HttpContextAccessor(); // Adds IHttpContextAccessor to DI
}

In Configure method:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    ...
    app.UseSession(); // Enables session for the application
    ...
}

In the ConfigureServices method, we add services for Session. We also inject an instance of IHttpContextAccessor into our application.

In the Configure method, we use the UseSession() method to enable sessions for the application.

2. Creating an API Controller

After setting up Startup.cs, let's create an API controller where we will set and retrieve session variables using Dependency Injection and the IHttpContextAccessor class.

[ApiController]
public class SessionController : ControllerBase
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    public SessionController(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }
}

We have injected IHttpContextAccessor into our controller using the constructor.

3. Setting Session Variables

Now, let’s create a method inside of our SessionController that will set a session variable:

[HttpPost]
public IActionResult SetSessionValue([FromBody] string value)
{
    _httpContextAccessor.HttpContext.Session.SetString("MySessionKey", value);

    return Ok();
}

Here, we’ve created a POST endpoint SetSessionValue. It accepts a value from the request body and sets it into session using key "MySessionKey".

4. Retrieving Session Variables

To retrieve our session variable, we’ll create another method:

[HttpGet]
public IActionResult GetSessionValue()
{
    var value = _httpContextAccessor.HttpContext.Session.GetString("MySessionKey");

    return Ok(value);
}

This GET endpoint GetSessionValue retrieves the value from the session using the key "MySessionKey".

And there you have it! You can now set and retrieve session variables within your C# API controllers using Dependency Injection and IHttpContextAccessor. This simple yet powerful functionality can greatly assist in creating stateful API interactions.

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