Injects look-through cache for configured services

// Cache results returned from MySlowService in Mem Cache
services.AddMethodCaching()
        .AddTransientWithCaching<IMySlowService, MySlowService, MyResult>();

var app = builder.Build();

// Configure method caching policies
var methodCachePolicies = app.Services.GetRequiredService<IMethodCacheOptionsLookup>();
methodCachePolicies.AddRelativeExpiration<IMySlowService>(TimeSpan.FromSeconds(30));

Suppose you have a slow service that fetches information on books by ISBN.

public interface IBookInfoService
{
    BookInfo GetBookInfo(string isbn);
}

class BookInfoService : IBookInfoService
{
    public BookInfo GetBookInfo(string isbn) { ... }
}

The service is slow and book information changes infrequently, so you would like to cache it. Rather than registering BookInfoService with .AddTransient you can use .AddTransientWithCaching.

services.AddMethodCaching()
        .AddTransientWithCaching<IBookInfoService, BookInfoService, BookInfo>();

The above will register a caching proxy for IBookInfoService which will wrap BookInfoService. The first call to get info on a particular book will use BookInfoService, but subsequent calls to get info on the same book will return the cached result from the first call.

void Example([Inject] IBookInfoService bookInfoService)
{
    var info1 = bookInfoService.GetBookInfo("1234");    // Slow. Saves cache entry using key "GetBookInfo(1234)"
    var info2 = bookInfoService.GetBookInfo("1234");    // Fast. Returns cache entry found using key "GetBookInfo(1234)"
    Assert.Equals(info1, info2);
}

Only one return type can be cached per service interface. This works well for services that implement a Single Responsibility, but not for larger classes. Often times simplified interface(s) can be created. The simplified interfaces may only have 1 function each and all be implemented by the large class.

Only the Transient lifetime is implemented.

A cache key is automatically generated from the method invocation based on the method name and passed arguments. For example: "IMyBookService.GetBookInfo('The Great Gatsby')". Other environment information is not included.

Be careful in multi-user or multi-tenant environments not to cache user-specific or tenant-specific results. For example, caching a method like GetCurrentUserFavoriteColor() would end up returning the same color for all users. To make it amenable to method caching change it to GetUserFavoriteColor(userId).

The programmer, like the poet, works only slightly removed from pure thought-stuff. He builds his castles in the air, from air, creating by exertion of the imagination. Few media of creation are so flexible, so easy to polish and rework, so readily capable of realizing grand conceptual structures.

— Fred P. Brooks