@mavenoid/dataloader

@mavenoid/dataloader

Utilities for caching, batching and deduping requests in GraphQL. Inspired by dataloader but extended using WeakMap to create a more convenient API for GraphQL

Installation

yarn add @mavenoid/dataloader

Usage

import {
  getDataLoadersForContextType,
  RequestsBatch,
} from '@mavenoid/dataloader';

const {batch, dedupe} = getDataLoadersForContextType<ResolverContextType>();

const getUserDeduped = dedupe(
  async (userID: number, _resolverContext: ResolverContextType) => {
    return await getUserUncached(userID);
  },
);

// You can load a user within a GraphQL resolver using:
//
//   getUserDeduped(userID, resolverContext)
//
// You can call this as many times as you like, and `getUserUncached` will only be called
// once per request.
//
// if you modify a user within a request, you can delete it from the cache using:
//
//   getUserDeduped.cache(resolverContext).delete(userID)
//
// or
//
//   getUserDeduped.cache(resolverContext).clear()

const getUserBatched = batch(
  async (userIDs: number[], _resolverContext: ResolverContextType) => {
    // load all the requested userIDs in one go, and then return a map from
    // the requested IDs to the results
    const users = await db_users.find({id: anyOf(userIDs)}).all();
    return new Map(users.map((user) => [user.id, user]));
  },
  {maxBatchSize: 100},
);

// You can load a user within a GraphQL resolver using:
//
//   getUserBatched(userID, resolverContext)
//
// You can call this as many times as you like, and the database will only be queried
// once per request. The requests will be batched so that up to 100 users are loaded
// at a time.
//
// if you modify a user within a request, you can delete it from the cache using:
//
//   getUserBatched.cache(resolverContext).delete(userID)
//
// or
//
//   getUserBatched.cache(resolverContext).clear()

Handling undefined

The batch methods return undefined for any requested records that are not included in the results. If this is not what you want, you can add a fallback using:

import {
  handleUndefinedResult,
  errorOnUndefinedResult,
} from '@mavenoid/dataloader';

const getUserOrNull = handleUndefinedResult(getUserBatched, () => null);
const getUserOrError = errorOnUndefinedResult(
  getUserBatched,
  (id) => `Could not find user: ${id}`,
);

Handling requests for lists of dependent records

The groupRecordsByKey can be used to group a list of records by a foreign key. It will preserve the order of the records within each group.

const getUserMessagesBatched = handleUndefinedResult(
  batch(
    async (userIDs: number[], _resolverContext: ResolverContextType) => {
      const messages = await db_messages
        .find({sender_id: anyOf(userIDs)})
        .all();
      return groupRecordsByKey(messages, (m) => m.sender_id);
    },
    {maxBatchSize: 100},
  ),
  () => [],
);