CODEWITHSUNDEEP
c#asp.net-core.net-core
Seyed Morteza Mousavi
Seyed Morteza Mousavi

Reputation: 6963

IMemoryCache does not save data at application startup

I created a fresh ASP.NET Core Web API project. Here is ConfigureServices in Startup.cs:

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
        services.AddMemoryCache();
        var serviceProvider = services.BuildServiceProvider();
        var cache = serviceProvider.GetService<IMemoryCache>();

        cache.Set("key1", "value1");
        //_cahce.Count is 1
    }

As you see I add an item to IMemoryCache. Here is my controller:

[Route("api/[controller]")]
[ApiController]
public class ValuesController : ControllerBase
{
    private readonly IMemoryCache _cache;
    public ValuesController(IMemoryCache cache)
    {
        _cache = cache;

    }
    [HttpGet("{key}")]
    public ActionResult<string> Get(string key)
    {
        //_cahce.Count is 0
        if(!_cache.TryGetValue(key, out var value))
        {
            return NotFound($"The value with the {key} is not found");
        }

        return value + "";
    }
}

When I request https://localhost:5001/api/values/key1, the cache is empty and I receive a not found response.

Upvotes: 3

Views: 2774

Answers (2)

Chris Pratt
Chris Pratt

Reputation: 239440

In short, the cache instance you're setting the value in is not the same as the one that is later being retrieved. You cannot do stuff like while the web host is being built (i.e. in ConfigureServices/Configure. If you need to do something on startup, you need to do it after the web host is built, in Program.cs:

public class Program
{
    public static void Main(string[] args)
    {
        var host = CreateWebHostBuilder(args).Build();

        var cache = host.Services.GetRequiredService<IMemoryCache>();
        cache.Set("key1", "value1");

        host.Run();
    }

    public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
 }

Upvotes: 6

jgoday
jgoday

Reputation: 2836

As @selloape saids, if you manullay call BuildServicesProvider, you are creating a new provider, that will be not used in your controllers.

You can use a hosted service to intialize your cache

    public class InitializeCacheService : IHostedService
    {
        private readonly IServiceProvider _serviceProvider;
        public InitializeCacheService (IServiceProvider serviceProvider)
        {
            _serviceProvider = serviceProvider;
        }

        public Task StartAsync(CancellationToken cancellationToken)
        {
            using (var scope = _serviceProvider.CreateScope())
            {
                var cache = _serviceProvider.GetService<IMemoryCache>();

                cache.Set("key1", "value1");
            }

            return Task.CompletedTask;
        }

        public Task StopAsync(CancellationToken cancellationToken)
        {
            return Task.CompletedTask;
        }
    }

Add it in your ConfigureServices

services.AddHostedService<InitializeCacheService>();

https://learn.microsoft.com/en-us/aspnet/core/fundamentals/host/hosted-services?view=aspnetcore-2.2

Upvotes: 4

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