What is caching in ASP.NET Core?

Question

Accepted Answer

**Caching** — store data for faster retrieval.

**IMemoryCache (in-memory):**
```csharp
// Registration
builder.Services.AddMemoryCache();

// Usage
public class ProductService
{
    private readonly IMemoryCache _cache;

public async Task<Product> GetProductAsync(int id)
    {
        return await _cache.GetOrCreateAsync(
            $"product_{id}",
            async entry =>
            {
                entry.AbsoluteExpirationRelativeToNow =
                    TimeSpan.FromMinutes(5);
                return await _repo.GetByIdAsync(id);
            });
    }
}
```

**IDistributedCache (Redis/SQL):**
```csharp
// Registration
builder.Services.AddStackExchangeRedisCache(options =>
{
    options.Configuration = "localhost:6379";
    options.InstanceName = "master_";
});

// Usage
var cachedData = await _distributedCache.GetStringAsync("key");
if (cachedData == null)
{
    cachedData = JsonSerializer.Serialize(data);
    await _distributedCache.SetStringAsync("key", cachedData);
}
```

**Output caching (minimal APIs):**
```csharp
app.MapGet("/products", async (IDbContext db) =>
{
    return await db.Products.ToListAsync();
})
.CacheOutput(TimeSpan.FromMinutes(10));
```

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