UserPermissionsLoader.js

import DataLoader from 'dataloader';

import UserPermission from '../../../models/user-permission.model';

async function batchUserPermissions(userIds) {
  const userPermissionListMap = new Map();

  const userPermissions = await UserPermission.query()
    .select(['userId', 'permission'])
    .whereIn('userId', userIds);

  userPermissions.forEach(({ userId, permission }) => {
    if (userPermissionListMap.has(userId)) {
      userPermissionListMap.get(userId).push(permission);
    } else {
      userPermissionListMap.set(userId, [permission]);
    }
  });

  return userIds.map(userId => userPermissionListMap.get(userId) || []);
}

export default function createUserPermissionsLoader() {
  return new DataLoader(batchUserPermissions);
}