How to load data when .net core 6.0 web api app started?

Question

I'd like to load file data into cache memory on program.cs(.net core 6.0) and loaded data will use in many services.

So I typed builder.Services.AddMemoryCache(); into source code.

But and then, I don't know how to use this memory cache in right there(in program.cs).

In the previous version, with Configure method and IMemoryCache cache parameter I can load data with memory cache like following code block

public void Configure(IMemoryCache cache)
{
    cache.set(...);
    cache.get(...);
}

I'm developing with .net core 6.0 web api. Does anybody know how to init data on program.cs in .net core 6.0?

So you want to write an `IHostedService` / `BackgroundService` to run on host startup? Though you might want to wait until `IHostApplicationLifetime.ApplicationStarted` if you want to handle requests while warming up the cache. — Jeremy Lakeman, May 17 '22 at 01:01
@JeremyLakeman Thanks for your reply. I'm new to handle .net core framework. I'm studying now. So can you suggest any link that I can learn to write `IHostService`/`BackgroundService` ? — takeyourcode, May 17 '22 at 01:05
The first google result is a good place to start. https://learn.microsoft.com/en-us/aspnet/core/fundamentals/host/hosted-services?view=aspnetcore-6.0&tabs=visual-studio Which shows a couple common use cases, covering many FAQ. — Jeremy Lakeman, May 17 '22 at 01:07
@JeremyLakeman Thank you! I'm just curious about this... Is this the general way to init data on starting server? — takeyourcode, May 17 '22 at 01:09
For lazy init after the api is available, there's also https://stackoverflow.com/a/66996436/4139809, but that's harder to unit test. — Jeremy Lakeman, May 17 '22 at 01:14

Qing Guo · Accepted Answer · 2022-05-17T05:54:38.937

Below is a work demo, you can refer to it.

Option 1

Do it after the web host is built, in Program.cs:

...
builder.Services.AddMemoryCache();
var app = builder.Build();
var cache=app.Services.GetRequiredService<IMemoryCache>();
cache.Set("key1", "value1");
...

Option 2

Use a hosted service to intialize 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;
        }
    }

In Program.cs, add below code:

builder.Services.AddMemoryCache();
builder.Services.AddHostedService<InitializeCacheService>();

ValuesController (Two options all use this 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 + "";
        }
    }

Result:

Update

I tried to apply option 1, but It didn't worked. What is different for your answer, I wrapped requiredservice line and cache.set/get line with `using (var scope = app.Services.CreateScope())` . Is it problem? — takeyourcode, May 17 '22 at 05:08
Can you share more code you used? And the error you meet ? @takeyourcode — Qing Guo, May 17 '22 at 05:29
`using (var scope = app.Services.CreateScope()) { var services = scope.ServiceProvider; var context = services.GetRequiredService(); context.Set("test", "aaaaaa"); Console.WriteLine(context.Get("test")); } ` And console output was empty but your solution working well. Is it problem? — takeyourcode, May 17 '22 at 05:43
@takeyourcode I try your code, but console output has aaaaaa. — Qing Guo, May 17 '22 at 05:55
Gua It is so weird.. Ok anyway I'll try it again. And I'll try your option 2 for my skill as well. Good luck to you! — takeyourcode, May 17 '22 at 15:52
It was my mistake.. I checked It is working well. Really thanks for your reply! — takeyourcode, May 17 '22 at 16:21

How to load data when .net core 6.0 web api app started?

1 Answers1