Caching

DataLoader provides a memoization cache for all loads which occur in a single request to your application.

• After .load() is called once with a given key, the resulting value is cached.

The cache only serves the purpose of not repeatedly loading the same data in the context of a single request to your Application.

Dataloader maintains a simple in-memory memoization cache.

• more accurately: .load() itself is a memoized function.

// creating loader
function createLoaders(authToken) {
  return {
    users: new DataLoader(ids => genUsers(authToken, ids)),
  };
}

const app = express();

app.get('/', function (req, res) {
  const authToken = authenticateUser(req);
  const loaders = createLoaders(authToken);
  res.send(renderPage(req, loaders));
});

app.listen();

// caching example
userLoader.prime(1, { bestFriend: 3 });

async function getBestFriend(userID) {
  const user = await userLoader.load(userID);
  return await userLoader.load(user.bestFriendID);
}

// In one part of your application
getBestFriend(1);

// Elsewhere
getBestFriend(2);

Lifecycle

Typically, DataLoader instances are created when a Request begins, and are not used once the Request ends.

clear() and clearAll() invalidate the cached value at key(s).