[FEATURE] Make setting up NullFusionCache easier in ASP.NET

[esd-thg]

Problem

Configuring FusionCache in a test scenario isn't as straight forward at it could be :)

I found NullFusionCache via issues and discussions.
I then had to guess how I should use/configure it.

Solution

Add some docs in docs/Testing.md 😄 (or similar)
So it's easier to find and figure out the best way to configure it.

Alternatives

Could also consider making an extension helper

builder.Services.AddNullFusionCache();

or something like that

Additional context

Be mindful of the AsHybridCache. It doesn't inject IFusionCache

FusionCache/src/ZiggyCreatures.FusionCache/FusionCacheBuilderExtMethods.cs

Line 1498 in 02e5177

return new FusionHybridCache(builder.Build(sp));

So replacing IFusionCache with the NullFusionCache doesn't work when using AsHybridCache as it'll still use whatever cache was configured first.

That means that this won't work

services.Replace(
    ServiceDescriptor.Singleton<IFusionCache>(_ => new NullFusionCache(new FusionCacheOptions()))
);

I had to do this:

services.Replace(
    ServiceDescriptor.Singleton<IFusionCache>(_ => new NullFusionCache(new FusionCacheOptions()))
);
services.Replace(
    ServiceDescriptor.Singleton<HybridCache>(sp => new FusionHybridCache(
        sp.GetRequiredService<IFusionCache>()
    ))
);

Perhaps AsHybridCache can be changed to

return new FusionHybridCache(sp.GetRequiredService<IFusionCache>());

[jodydonetti]

Hi @eskild-th

Problem

Configuring FusionCache in a test scenario isn't as straight forward at it could be :)

Thanks for letting me know, I'd like to take this opportunity to push more for it then 🙂

Solution

Add some docs in docs/Testing.md 😄 (or similar) So it's easier to find and figure out the best way to configure it.

You're right, makes total sense!
It should also touch on the mocking aspect of it: not everybody uses mocking, but it came up multiple times in the past and I think the time has come for me to expand on it.

Alternatives

Could also consider making an extension helper

builder.Services.AddNullFusionCache();
or something like that

I was about to ask you if you tried with services.AddFusionCache(new NullFusionCache(...)) but then I remembered that that ext method does not return a builder where you can chain a call to .AsHybridCache(), so... I have to think about something else.

Additional context

Be mindful of the AsHybridCache. It doesn't inject IFusionCache
[...]
return new FusionHybridCache(builder.Build(sp));
So replacing IFusionCache with the NullFusionCache doesn't work when using AsHybridCache as it'll still use whatever cache was configured first.

Yes, that is because I need to support Named Caches.

Let me think about something, I'll update you on this.

Thanks for pointing this out!

[jodydonetti]

Hi @eskild-th I created an issue to keep track of the new feature.
The implementation is already done, the new tests are there and everything seems to work well.

[jodydonetti]

Hi all, v2.2.0-preview-1 is out 🥳

[esd-thg]

That was fast! Thank you so much

[jodydonetti]

If you can try it in your scenario and let me know if it works well that would be great: if something comes out I can make changes before going GA.

Thanks!

[esd-thg]

I'm not sure how to utilize WithNullImplementation in the WebApplicationFactory

Given this test setup

public class CustomWebApplicationFactory : WebApplicationFactory<Program>
{
    protected override void ConfigureWebHost(IWebHostBuilder builder)
    {
        builder.ConfigureServices(services =>
        {
            // disable caching
            services.AddFusionCache().WithNullImplementation();
        });

        builder.UseEnvironment("Development");
    }
}

I'm still getting a FusionCache injected.

With

public class CustomWebApplicationFactory : WebApplicationFactory<Program>
{
    protected override void ConfigureWebHost(IWebHostBuilder builder)
    {
        builder.ConfigureServices(services =>
        {
            // disable caching
            services.Replace(
                ServiceDescriptor.Singleton<IFusionCache>(_ => new NullFusionCache(new FusionCacheOptions()))
            );
            services.Replace(
                ServiceDescriptor.Singleton<HybridCache>(sp => new FusionHybridCache(
                    sp.GetRequiredService<IFusionCache>()
                ))
            );
        });

        builder.UseEnvironment("Development");
    }
}

I'm getting a NullFusionCache.

What is the intended way to alter/replace FusionCache inside WebApplicationFactory?

[jodydonetti]

Hi @eskild-th

I'm not sure how to utilize WithNullImplementation in the WebApplicationFactory
[...]
What is the intended way to alter/replace FusionCache inside WebApplicationFactory?

Wait, what do you mean "alter/replace"?

Did you already registered FusionCache with a "normal" AddFusionCache() and then trying to change it later? That wouldn't work, it's not how DI in .NET works, at least it's not the "normal" behaviour.

You can change it later (but still before building the ServiceProvider) in the way you are already doing it with services.Replace(...) although it's kinda "hacky".

In general I would suggest to do different things based on some conditions during registration, not after, meaning when you are registering FusionCache you can tell it to use the null implementation.

Something like:

var builder = services.AddFusionCache()
  .WithWhatever1(...)
  .WithWhatever2(...);

if (%CONDITION%) {
  builder.WithNullImplementation();
}

Makes sense?

[esd-thg]

Wait, what do you mean "alter/replace"?

Did you already registered FusionCache with a "normal" AddFusionCache() and then trying to change it later? That wouldn't work, it's not how DI in .NET works, at least it's not the "normal" behaviour.

To my understanding it's the normal approach when setting up ASP.NET tests.
You configure your services as expected in Program.cs. That would be services.AddFusionCache() etc.

Then when configuring tests you mock services by replacing them in the DI - at least when doing integration testing.
The ASP.NET team have made this easy by providing WebApplicationFactory which "alters" the normal setup in Program.cs so it's ready for testing.

https://learn.microsoft.com/en-us/aspnet/core/test/integration-tests?view=aspnetcore-9.0

They showcase a setup where they replace the normal database with Sqlite, which is sort of similar to replacing the normal cache with a NullCache

public class CustomWebApplicationFactory<TProgram>
    : WebApplicationFactory<TProgram> where TProgram : class
{
    protected override void ConfigureWebHost(IWebHostBuilder builder)
    {
        builder.ConfigureServices(services =>
        {
            var dbContextDescriptor = services.SingleOrDefault(
                d => d.ServiceType == 
                    typeof(IDbContextOptionsConfiguration<ApplicationDbContext>));

            services.Remove(dbContextDescriptor);

            var dbConnectionDescriptor = services.SingleOrDefault(
                d => d.ServiceType ==
                    typeof(DbConnection));

            services.Remove(dbConnectionDescriptor);

            // Create open SqliteConnection so EF won't automatically close it.
            services.AddSingleton<DbConnection>(container =>
            {
                var connection = new SqliteConnection("DataSource=:memory:");
                connection.Open();

                return connection;
            });

            services.AddDbContext<ApplicationDbContext>((container, options) =>
            {
                var connection = container.GetRequiredService<DbConnection>();
                options.UseSqlite(connection);
            });
        });

        builder.UseEnvironment("Development");
    }
}

https://learn.microsoft.com/en-us/aspnet/core/test/integration-tests?view=aspnetcore-9.0#customize-webapplicationfactory

Something like:

var builder = services.AddFusionCache()
.WithWhatever1(...)
.WithWhatever2(...);

if (%CONDITION%) {
builder.WithNullImplementation();
}

This would make my real program aware of when it's running tests.
Taking this argument to the extreme would make my code look like this:

if (isTesting)
  // not real logic
else
  // do normal logic

My point being. Code should not have conditions based on whether or not it's being run in a test.

[jodydonetti]

Hi @eskild-th I now understand better what you meant, thanks a lot.
Will update you during the weekend.

[esd-thg]

Much appreciated! But no need to rush :)
I'll be offline for about week so I won't be able to give feedback until I'm back ⛱

[jodydonetti]

Hi @eskild-th , I'm coming back to this, and there's one thing that I don't understand.

Could also consider making an extension helper

builder.Services.AddNullFusionCache();
or something like that

How would that fit into the whole "replacing services instead of registering a null impl directly"?

I'm asking because what I did is basically the same (services.AddFusionCache().WithNullImplementation() instead of services.AddNullFusionCache()) and I'm trying to understand how to connect the dots.

Thanks!