Struct Loader

pub struct Loader<K, V>
where
    K: 'static + Eq + Debug + Copy + Send,
    V: 'static + Send + Debug + Clone,
{ /* private fields */ }

Batch loads values from some expensive resource, primarily intended for mitigating GraphQL’s N+1 problem.

Users can call Loader::load and Loader::load_many to fetch values from the underlying resource or cache. The cache can be cleared with calls to Loader::clear and Loader::clear_many, and values can be added to the cache out-of-band through the use of Loader::prime and Loader::prime_many.

The Loader struct acts as an intermediary between the async domain in which load calls are invoked and the pseudo-single-threaded domain of the LoaderWorker. Callers can invoke the Loader from multiple parallel tasks, and the loader will enqueue the requested operations on the request queue for processing by its LoaderWorker. The worker processes the requests sequentially and provides results via response oneshot channels back to the Loader.

Implementations

impl<K, V> Loader<K, V>

where K: 'static + Eq + Debug + Ord + Copy + Hash + Send + Sync, V: 'static + Send + Debug + Clone,

pub fn new<F, ContextT>(_: F, context: ContextT) -> Self

where ContextT: Send + Sync + 'static, F: 'static + BatchFunction<K, V, Context = ContextT> + Send,

Creates a new Loader for the provided BatchFunction and Context type.

Note: the batch function is passed in as a marker for type inference.

impl<K, V> Loader<K, V>

where K: 'static + Eq + Debug + Ord + Copy + Send + Sync, V: 'static + Send + Debug + Clone,

pub async fn load(&self, key: K) -> Option<V>

Loads a value from the underlying resource.

Returns None if the value could not be loaded by the BatchFunction.

If the value is already in the loader cache, it is returned as soon as it is processed. Otherwise, the requested key is enqueued for batch loading in the next loader execution frame.

pub async fn load_many(&self, keys: Vec<K>) -> Vec<Option<V>>

Loads many values at once.

Returns None for values that could not be loaded by the BatchFunction.

If all the values are already present in the laoder cache, they are returned as soon as the request is processed by the worker. Otherwise, the keys is enqueue for batch loading in the next loader execution frame.

pub async fn prime(&self, key: K, value: V)

Adds a value to the cache.

pub async fn prime_many(&self, key_vals: Vec<(K, V)>)

Adds many values to the cache at once.

pub async fn clear(&self, key: K)

Removes a value from the cache.

This key will be reloaded when it is next requested.

pub async fn clear_many(&self, keys: Vec<K>)

Removes multiple values from the cache at once.

These keys will be reloaded when requested.

Trait Implementations

impl<K, V> Drop for Loader<K, V>

where K: 'static + Eq + Debug + Copy + Send, V: 'static + Send + Debug + Clone,

fn drop(&mut self)

Executes the destructor for this type.