What is output caching in ASP.NET Core?

Question

Accepted Answer

**Output caching** — cache complete HTTP responses.

**Setup:**
```csharp
builder.Services.AddOutputCache();
app.UseOutputCache();
```

**Per-endpoint:**
```csharp
app.MapGet("/products", async (IDbContext db) =>
    await db.Products.ToListAsync())
    .CacheOutput(TimeSpan.FromMinutes(10));
```

**Cache policies:**
```csharp
builder.Services.AddOutputCache(options =>
{
    options.AddBasePolicy(builder =>
        builder.Expire(TimeSpan.FromMinutes(5)));

options.AddPolicy("ProductCache", builder =>
        builder
            .Expire(TimeSpan.FromMinutes(10))
            .Tag("products"));
});
```

**Invalidation:**
```csharp
app.MapPost("/products", async (...) =>
{
    // Create product...
    await ctx.RequestServices
        .GetRequiredService<OutputCacheInvalidationManager>()
        .InvalidateTagAsync("products");
});
```

**Vary by:** query string, header, route value.

C#: What is output caching in ASP.NET Core?