Loading¶

Otter provides a Loader interface that supports loading values from external sources into the cache when they are not present. This allows you to automatically populate the cache with data as needed. The Loader implementation should always return ErrNotFound if the entry was not found in the data source.

// Define a loader function
loader := otter.LoaderFunc[string, string](func(ctx context.Context, key string) (string, error) {
    // Load value from external source
    return "loaded value", nil
})

// Get a value, loading it if not present
value, err := cache.Get(context.Background(), "key", loader)

If you use RefreshCalculator, the cache will try to refresh the stale entries. You can find more detailed examples in the following chapter.