Keys

Key is an identifier used to uniquely represent the data you want to fetch.

const DataLoader = require('frontend/contents/graphql/dataloader/a.start');

async function batchUsers(userIds) {
  // Fetch users in bulk using the array of user IDs
  const users = await getUsersByIds(userIds);

  return userIds.map(id => users.find(user => user.id === id));
}

// Create a DataLoader for users
const userLoader = new DataLoader(keys => batchUsers(keys));

const resolvers = {
  Query: {
    // The `id` is the key
    user: (parent, { id }) => userLoader.load(id)
  }
};

Use context arg to call the Dataloader to maintain single instance of Dataloader

const { createLoader } = require('./a.start'); // Function to create DataLoader

const resolvers = {
  Query: {
    users: async (_, args, context) => {
      // Create a new instance of DataLoader
      const userLoader = createLoader();

      // Fetch some users from a DB
      const users = await fetchUsers();

      // loads to DataLoader per request
      const usersWithPosts = await Promise.all(users.map(user => {
        return {
          ...user,
          posts: userLoader.load(user.id) // Load related data using DataLoader
        };
      }));
      return usersWithPosts;
    },
  },

  User: {
    posts: (parent, args, context) => {
      // previously defined loader is called here
      // Use DataLoader for batching and caching
      return context.userLoader.load(parent.id);
    },
  }
};