README.md

feathers-dataloader

Reduce requests to backend services by batching calls and caching records.

Installation

npm install feathers-dataloader --save

Documentation

Please refer to the documentation for more information.

• Documentation - Definitions for the classes exported from this library
• Guide - Common patterns, tips, and best practices

TLDR

Promise.all([
  app.service('posts').get(1),
  app.service('posts').get(2),
  app.service('posts').get(3)
]);

is slower than

app.service('posts').find({ query: { id: { $in: [1, 2, 3] } } });

Feathers Dataloader makes it easy and fast to write these kinds of queries. The loader handles coalescing all of the IDs into one request and mapping them back to the proper caller.

const loader = new AppLoader({ app: context.app });

Promise.all([
  loader.service('posts').load(1),
  loader.service('posts').load(2),
  loader.service('posts').load(3)
]);

is automatically converted to

app.service('posts').find({ query: { id: { $in: [1, 2, 3] } } });

Quick Start

const { AppLoader } = require('feathers-dataloader');

// See Guide for more information about how to better pass
// loaders from service to service.
const initializeLoader = context => {
  if (context.params.loader) {
    return context;
  }
  context.params.loader = new AppLoader({ app: context.app });
  return context;
}

// Use this app hook to ensure that a loader is always configured in
// your service hooks. You can now access context.params.loader in any hook.
app.hooks({
  before: {
    all: [initializeLoader]
  }
})


// Loaders are most commonly used in resolvers like @feathersjs/schema,
// withResults, or fastJoin. See the Guide section for more
// information and common usecases.
// Pass the loader to any and all service/loader calls. This maximizes
// performance by allowing the loader to reuse its cache and
// batching mechanism as much as possible.
const { resolveResult, resolve } = require('@feathersjs/schema');

const postResultsResolver = resolve({
  properties: {
    user: async (value, post, context) => {
      const { loader } = context.params;
      return await loader.service('users').load(post.userId, { loader });
    },
    category: async (value, post, context) => {
      const { loader } = context.params;
      return await loader.service('categories').key('name').load(post.categoryName, { loader });
    },
    tags: async (value, post, context) => {
      const { loader } = context.params;
      return await loader.service('tags').load(post.tagIds, { loader });
    },
    comments: async (value, post, context) => {
      const { loader } = context.params;
      return await loader.service('comments').multi('postId').load(post.id, { loader });
    }
  }
});


app.service('posts').hooks({
  after: {
    all: [resolveResult(postResultsResolver)]
  }
});

Running Tests

This package includes a .mocharc.js file, which means it supports VSCode debugging with Test Explorer UI and Mocha Test Explorer installed.

Once you've installed both plugins, you should see two ways to directly run tests.

• The "test beaker" icon in VSCode's main nav, which will show you a tree of all Mocha tests.
• A "run" and "debug" codelens link above every Mocha test.

License

Licensed under the MIT license.