Session not working in ASP.Net Core Web API

Question

I am trying to use the session capability in ASP.NET Core Web API (.NET Core 3.1). As a test, I configured my project as follows.

Install NuGet package Microsoft.AspNetCore.Session.
Add service methods in ConfigureServices in Startup.cs.

services.AddDistributedMemoryCache();
services.AddSession();

Use session in Configure in Startup.cs:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    app.UseSession();
    
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }

    app.UseHttpsRedirection();

    app.UseRouting();

    app.UseAuthorization();

    app.UseEndpoints(endpoints => { endpoints.MapControllers(); });
}

Set a session variable in one of my routes in my controller.

HttpContext.Session.SetString("currentUser", "value1");

However, I keep getting this error.

{"type":"NullReferenceException","message":"Object reference not set to an instance of an object.","stackTrace":" at Api.Routes.MainRoute.Handler(ILogger`1 logger) in MainRoute.cs:line 16\n at Api.Controllers.MainController.MainRoute(String authorization) in MainController.cs:line 264"}

How can I fix this problem?

Please post your entire Configure method - because the order of invocation of app. methods is important. — Dai
– Dai, Commented Sep 11, 2021 at 4:56
Please post the entire stack-trace of the NullReferenceException - what makes you so sure it's related to Session-state? — Dai
– Dai, Commented Sep 11, 2021 at 4:56
AddDistributedMemoryCache <-- why are you using the distributed memory-cache when you haven't configured the distributed cache client? (e.g. Redis, memcached, etc). Instead, for single and smaller web-applications you probably want just AddMemoryCache(). — Dai
– Dai, Commented Sep 11, 2021 at 4:57
I've done what you said. I used AddDistributedMemoryCache because it resolved an error like Unable to resolve service for type 'Microsoft.Extensions.Caching.Distributed.IDistributedCache' while attempting to activate 'Microsoft.AspNetCore.Session.DistributedSessionStore'. — Simon Rex
– Simon Rex, Commented Sep 11, 2021 at 5:55
Please read out the thread in Stackoverflow regarding sessions in API. Hopefully it will be helpful. — Ishtiaq
– Ishtiaq, Commented Sep 11, 2021 at 6:33

Farzad · Accepted Answer · 2022-04-15 20:09:46Z

2

The order of middleware is important. Call UseSession after UseRouting and before MapRazorPages and MapDefaultControllerRoute .

Session and state management

Change your code to this:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }

    app.UseHttpsRedirection();

    app.UseRouting();

    app.UseSession();

    app.UseAuthorization();

    app.UseEndpoints(endpoints => { endpoints.MapControllers(); });
}

answered Apr 15, 2022 at 20:09

Farzad

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Tiny Wang · Accepted Answer · 2021-09-13 08:51:22Z

1

I'm not sure but this document helped me to set session, and this is my startup file:

public void ConfigureServices(IServiceCollection services)
        {
            services.AddDistributedMemoryCache();

            services.AddSession(options =>
            {
                options.IdleTimeout = TimeSpan.FromSeconds(10);
                options.Cookie.HttpOnly = true;
                options.Cookie.IsEssential = true;
            });
            services.AddControllers();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            app.UseSession();
            app.UseHttpsRedirection();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }

answered Sep 13, 2021 at 8:51

Tiny Wang

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1 Comment

lyolikaa Over a year ago

On my project IdleTimeout was increased to fix same issue. Can be usefule in case of development or slowly performed API

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