lowdb

lowdb

Need a quick way to get a local database for a CLI, a small server or the browser?

Example

const low = require('lowdb')
const storage = require('lowdb/file-sync')
const db = low('db.json', { storage })

db('posts').push({ title: 'lowdb is awesome'})

Database is automatically saved to db.json

{
  "posts": [
    { "title": "lowdb is awesome" }
  ]
}

You can query and manipulate it using any lodash method.

db('posts').find({ title: 'lowdb is awesome' })

Examples use ES2015 syntax, it's supported by Node 5+. Node 0.12 is supported too but you need to use the older syntax.

// For Node 0.12
var db = low('db.json', { storage: storage })

Please note that lowdb can only be run in one instance of Node, it doesn't support Cluster.

Install

npm install lowdb --save

Features

• Very small (~100 lines for core)
• lodash API
• Extendable:
  • Custom storage (file, browser, in-memory, ...)
  • Custom format (JSON, BSON, YAML, ...)
  • Mixins (id support, ...)
  • Encryption

Lowdb is also very easy to learn since it has only a few methods and properties.

lowdb powers json-server package, jsonplaceholder website and many other great projects.

Usage examples

Depending on the context, you can use different storages and formats.

Lowdb comes bundled with file-sync, file-async and browser storages, but you can also write your own if needed.

CLI

For CLIs, it's easier to use lowdb/file-sync synchronous file storage .

const low = require('lowdb')
const storage = require('lowdb/file-sync')

const db = low('db.json', { storage })

db('users').push({ name: 'typicode' })
const user = db('users').find({ name: 'typicode' })

Server

For servers, it's better to avoid blocking requests. Use lowdb/file-async asynchronous file storage.

Important

• When you modify the database, a Promise is returned.
• When you read from the database, the result is immediately returned.

const low = require('lowdb').
const storage = require('lowdb/file-async')

const db = low('db.json', { storage })

app.get('/posts/:id', (req, res) => {
  // Returns a post
  const post = db('posts').find({ id: req.params.id })
  res.send(post)
})

app.post('/posts', (req, res) => {
  // Returns a Promise that resolves to a post
  db('posts')
    .push(req.body)
    .then(post => res.send(post))
})

Browser

In the browser, lowdb/browser will add localStorage support.

const low = require('lowdb')
const storage = require('lowdb/browser')

const db = low('db', { storage })

db('users').push({ name: 'typicode' })
const user = db('users').find({ name: 'typicode' })

In-memory

For the best performance, use lowdb in-memory storage.

const low = require('lowdb')
const db = low()

db('users').push({ name: 'typicode' })
const user = db('users').find({ name: 'typicode' })

Please note that, as an alternative, you can also disable writeOnChange if you want to control when data is written.

API

low([filename, [storage, [writeOnChange = true]]])

Creates a new database instance. Here are some examples:

low()                                      // in-memory
low('db.json', { storage: /* */ })         // persisted
low('db.json', { storage: /* */ }, false)  // auto write disabled

// To create read-only or write-only database,
// set only storage.read or storage.write
const fileSync = require('lowdb/fileSync')

// write-only
low('db.json', {
  storage: { write: fileSync.write }
})

// read-only
low('db.json', {
  storage: { read: fileSync.read }
})

You can also define custom storages and formats:

const myStorage = {
  read: (source, deserialize) => // obj or a Promise
  write: (dest, obj, serialize) => // undefined or a Promise
}

const myFormat = {
  format: {
    deserialize: (data) => // obj
    serialize: (obj) => // data
  }
}

low(source, { storage: myStorage, format: myFormat }, writeOnChange)

db._

Database lodash instance. Use it to add your own utility functions or third-party mixins like underscore-contrib or underscore-db.

db._.mixin({
  second: function(array) {
    return array[1]
  }
})

const post1 = db('posts').first()
const post2 = db('posts').second()

db.object

Use whenever you want to access or modify the underlying database object.

db.object // { posts: [ ... ] }

If you directly modify the content of the database object, you will need to manually call write to persist changes.

// Delete an array
delete db.object.posts
db.write()

// Drop database
db.object = {}
db.write()

db.write([source])

Persists database using storage.write method. Depending on the storage, it may return a promise.

Note: by default, lowdb automatically calls it when database changes.

const db = low('db.json', { storage })
db.write()            // writes to db.json
db.write('copy.json') // writes to copy.json

db.read([source])

Reads source using storage.read method. Depending on the storage, it may return a promise.

const db = low('db.json', { storage })
db.read()            // re-reads db.json
db.read('copy.json') // reads copy.json

Guide

How to query

With lowdb, you get access to the entire lodash API, so there is many ways to query and manipulate data. Here are a few examples to get you started.

Please note that data is returned by reference, this means that modifications to returned objects may change the database. To avoid such behaviour, you need to use .cloneDeep().

Also, the execution of chained methods is lazy, that is, execution is deferred until .value() is called.

Examples

Sort the top five posts.

db('posts')
  .chain()
  .filter({published: true})
  .sortBy('views')
  .take(5)
  .value()

Retrieve post titles.

db('posts').map('title')

Get the number of posts.

db('posts').size()

Make a deep clone of posts.

db('posts').cloneDeep()

Update a post.

db('posts')
  .chain()
  .find({ title: 'low!' })
  .assign({ title: 'hi!'})
  .value()

Remove posts.

db('posts').remove({ title: 'low!' })

How to use id based resources

Being able to retrieve data using an id can be quite useful, particularly in servers. To add id-based resources support to lowdb, you have 2 options.

underscore-db provides a set of helpers for creating and manipulating id-based resources.

const db = low('db.json')

db._.mixin(require('underscore-db'))

const postId = db('posts').insert({ title: 'low!' }).id
const post = db('posts').getById(postId)

uuid is more minimalist and returns a unique id that you can use when creating resources.

const uuid = require('uuid')

const postId = db('posts').push({ id: uuid(), title: 'low!' }).id
const post = db('posts').find({ id: postId })

How to use custom format

By default, lowdb storages will use JSON to parse and stringify database object.

But it's also possible to specify custom format.serializer and format.deserializer methods that will be passed by lowdb to storage.read and storage.write methods.

For example, if you want to store database in .bson files (MongoDB file format):

const low = require('lowdb')
const storage = require('lowdb/file-sync')
const bson = require('bson')
const BSON = new bson.BSONPure.BSON()

low('db.bson', { storage, format: {
  serialize: BSON.serialize
  deserialize: BSON.deserialize
})

// Alternative ES2015 short syntax
const bson = require('bson')
const format = new bson.BSONPure.BSON()
low('db.bson', { storage, format })

How to encrypt data

Simply encrypt and decrypt data in format.serialize and format.deserialize methods.

For example, using cryptr:

const Cryptr = require("./cryptr"),
const cryptr = new Cryptr('my secret key')

const db = low('db.json', {
  format: {
    deserialize: (str) => {
      const decrypted = cryptr.decrypt(str)
      const obj = JSON.parse(decrypted)
      return obj
    },
    serialize: (obj) => {
      const str = JSON.stringify(obj)
      const encrypted = cryptr.encrypt(str)
      return encrypted
    }
  }
})

Changelog

See changes for each version in the release notes.

Limits

lowdb is a convenient method for storing data without setting up a database server. It is fast enough and safe to be used as an embedded database.

However, if you seek high performance and scalability more than simplicity, you should probably stick to traditional databases like MongoDB.

License

MIT - Typicode