Memory Cache Integration snippet is misleading

[PashaPash]

Type of issue

Code doesn't work

Description

The snippet about changing the default cache size is misleading and misses UseMemoryCache, which you need to make EF use your custom cache instance.

Current snippet:

public void ConfigureServices(IServiceCollection services)
{
    services.AddMemoryCache(options => options.SizeLimit = 20480); // Custom size limit for EF Core caching
    
    services.AddDbContext<ApplicationDbContext>(options =>
        options.UseSqlServer(connectionString));
}

Correct version:

public void ConfigureServices(IServiceCollection services)
{
    services.AddMemoryCache(options => options.SizeLimit = 20480); // Custom size limit for EF Core caching

    services.AddDbContext<TContext>((serviceProvider, options) =>
    {
        options.UseMemoryCache(serviceProvider.GetRequiredService<IMemoryCache>());
        ///...
    });
}

Page URL

https://learn.microsoft.com/en-us/ef/core/performance/advanced-performance-topics?tabs=with-di%2Cexpression-api-with-constant#memory-cache-integration

Content source URL

https://github.com/dotnet/EntityFramework.Docs/blob/main/entity-framework/core/performance/advanced-performance-topics.md

Document Version Independent Id

e96b453f-0256-8bc9-bd21-1343f2fe246c

Platform Id

ada64a4c-83c3-6714-0fa4-d80a203f4349

Article author

@roji

[AndriySvyryd]

No, the current snippet is correct you don't need to call UseMemoryCache.
UseMemoryCache is only needed if you didn't add an IMemoryCache in the app service provider or wish to use a different one for EF.

[PashaPash]

@AndriySvyryd that is definitely not the case; it can be verified with the following snippet.
It prints the default size (10240) unless I call UseMemoryCache or use options.UseInternalServiceProvider.

If it is expected to use an external cache, should I post this as an issue to the EF Core repo instead?

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.Extensions.Caching.Memory;
using Microsoft.Extensions.DependencyInjection;
using System.Reflection;

var services = new ServiceCollection();

services.AddLogging();
services.AddMemoryCache(options => options.SizeLimit = 20480);

services.AddEntityFrameworkInMemoryDatabase();

services.AddDbContext<EmptyDbContext>((serviceProvider, options) =>
{
	options.UseInMemoryDatabase("demo-db");
});

using var serviceProvider = services.BuildServiceProvider(validateScopes: true);
using var scope = serviceProvider.CreateScope();
using var context = scope.ServiceProvider.GetRequiredService<EmptyDbContext>();

var dbContextOptions = context.GetService<IDbContextOptions>();
var coreOptions = dbContextOptions.FindExtension<CoreOptionsExtension>();
var memoryCache = context.GetService<IMemoryCache>();
var memoryCacheOptions = GetMemoryCacheOptions(memoryCache);

// prints 10240
Console.WriteLine(memoryCacheOptions.SizeLimit);

return;

static MemoryCacheOptions GetMemoryCacheOptions(IMemoryCache memoryCache)
{
	if (memoryCache is not MemoryCache concreteMemoryCache)
	{
		throw new InvalidOperationException($"Expected {typeof(MemoryCache).FullName}, but got {memoryCache.GetType().FullName}.");
	}

	var optionsField = typeof(MemoryCache).GetField("_options", BindingFlags.Instance | BindingFlags.NonPublic);
	var options = optionsField?.GetValue(concreteMemoryCache) as MemoryCacheOptions;

	return options ?? throw new InvalidOperationException("Could not read MemoryCacheOptions from the EF Core internal memory cache instance.");
}

internal sealed class EmptyDbContext(DbContextOptions<EmptyDbContext> options) : DbContext(options);

[PashaPash]

@AndriySvyryd Also, your resolution contradicts the documentation at https://learn.microsoft.com/en-us/dotnet/api/microsoft.entityframeworkcore.dbcontextoptionsbuilder.usememorycache?view=efcore-10.0#remarks
, which states that an internally resolved memory cache is used unless an external service provider is enforced with UseInternalServiceProvider.

[AndriySvyryd]

You are right! We changed this behavior a long time ago and didn't update the documentation