Batching

Batching consolidates multiple requests to a single request when it calls the same data source.

Batching accepts an array of keys, and returns a Promise that resolves to an Array of values.

Before data loaders can work properly, data source (whether another API, or a database) needs to implement a method that accepts multiple keys (such as IDs), and returns multiple objects (batching function).

const DataLoader = require('dataloader');

// supply batching function
const userLoader = new DataLoader(keys => myBatchGetUsers(keys));

// loading data-loaded data
const user = await userLoader.load(1);
const invitedBy = await userLoader.load(user.invitedByID);

// Elsewhere in your application
const user = await userLoader.load(2);
const lastInvited = await userLoader.load(user.lastInvitedID);

In the example above, a naive approach will make four round trips, but Dataloader will make at most two.