LevelUP

feathers-levelup is a database adapter for the fast and simple LevelDB, though many other backing stores are supported by supplying options to your LevelUP instances.

LevelUP backing store → LevelUP instance → Feathers service

LevelDB is a key-value database that stores its keys in lexicographical order, allowing for efficient range queries. Because LevelDB can only stream results in the order they are stored, avoid using $sort in your find calls, as the entire keyspace may be loaded for an in-memory sort. Read further to learn about ordering your LevelDB keys and designing your application around efficient range queries.

LevelUP currently supports the following backing stores:

• LevelDB
• Amazon DynamoDB
• AsyncStorage
• Basho's LevelDB Fork
• Google Sheets
• localStorage
• In-memory LRU Cache
• IndexedDB
• JSON Files
• Knex (sqlite3, postgres, mysql, websql)
• Medea
• Memory
• MongoDB
• MySQL
• Redis
• Riak
• RocksDB
• Windows Azure Table Storage

Installation

npm install levelup leveldown feathers-levelup --save

Getting Started

Creating a LevelUP service:

const levelup = require('levelup');
const levelupService = require('feathers-levelup');

// this will create a database on disk under ./todos
const db = levelup('./todos', { valueEncoding: 'json' });

app.use('/todos', levelupService({ db: db }));

See the LevelUP Guide for more information on configuring your database, including selecting a backing store.

Key Order

By default, LevelDB stores records on disk sorted by key. Storing sorted keys is one of the distinguishing features of LevelDB, and the LevelUP interface is designed around it.

When records are created, a key is generated based on a the value of options.sortField, plus a uuid. By default, _createdAt is automatically set on each record and its value is prepended to the key (id).

Change the sortField option to the field of your choice to configure your database's key ordering:

app.use('todos', service({
  db: db,
  sortField: '_createdAt', // this field value will be prepended to the db key
  paginate: {
    default: 2,
    max: 4
  }
}));

const todos = app.service('todos');

todos
  .create({task: 'Buy groceries'})
  .then(console.log);

{ task: 'Buy groceries',
  _createdAt: 1457923734510,
  id: '1457923734510:0:d06afc7e-f4cf-4381-a9f9-9013a6955562' }

Range Queries

Avoid memory-hungry _find calls that load the entire key set for processing by not specifying $sort, or by setting it to the same field as options.sortField. This way _find can take advantage of the natural sort order of the keys in the database to traverse the fewest rows.

Use $gt, $gte, $lt, $lte and $limit to perform fast range queries over your data.

app.use('todos', service({
  db: db,
  sortField: '_createdAt' // db keys are sorted by this field value
  paginate: {
    default: 2,
    max: 4
  }
}));

const todos = app.service('todos');

todos
  .find({
    query: {
      _createdAt: {
        $gt: '1457923734510'    // keys starting with this _createdAt
      },
      $limit: 10,               // load the first ten
      $sort: {
        _createdAt: 1           // sort by options.sortField (or don't pass $sort at all)
      }
    }
  })

Complete Example

Here's a complete example of a Feathers server with a message levelup service.

const service = require('./lib');
const levelup = require('levelup');
const feathers = require('feathers');
const rest = require('feathers-rest');
const bodyParser = require('body-parser');
const socketio = require('feathers-socketio');

// Create a feathers instance.
const app = feathers()
  // Enable Socket.io
  .configure(socketio())
  // Enable REST services
  .configure(rest())
  // Turn on JSON parser for REST services
  .use(bodyParser.json())
  // Turn on URL-encoded parser for REST services
  .use(bodyParser.urlencoded({extended: true}));

// Connect to the db, create and register a Feathers service.
app.use('messages', service({
  db: levelup('./messages', { valueEncoding: 'json' }),
  paginate: {
    default: 2,
    max: 4
  }
}));

app.listen(3030);
console.log('Feathers Message levelup service running on 127.0.0.1:3030');