node-flat-db

This is a fork of lowdb before they broke the api and no longer is as stable as before (fork of 12.5 lowdb)

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

Example

const flat = require('node-flat-db')
const storage = require('node-flat-db/file-sync')
 
const db = flat('db.json', { storage })
 
db('posts').push({ title: 'node-flat-db is awesome'})

Database is automatically saved to db.json.

{
  "posts": [
    { "title": "node-flat-db is awesome" }
  ]
}

You can query and manipulate it using any lodash method.

db('posts').find({ title: 'node-flat-db is awesome' })

And access underlying database object any time.

db.object.posts

Click here to try node-flat-db in the browser.

ES2015

Examples use ES2015 syntax for convenience, but you can use ES5 syntax too. For example:

var db = flat('db.json', { storage: storage })

Please note also that node-flat-db can only be run in one instance of Node, it doesn't support Cluster.

Installation

Using npm:

npm install node-flat-db --save

A standalone UMD build is also available on npmcdn:

<script src="http://npmcdn.com/node-flat-db@^0.2.0/dist/node-flat-db.min.js"></script>
<script>
  var db = flat() // in-memory
  var db = flat('db', { storage: flat.localStorage }) // localStorage
</script> 

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

node-flat-db is also very easy to learn since it has only a few methods and properties.

node-flat-db powers json-server package, jsonplaceholder website and many other great projects.

Usage examples

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

node-flat-db 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 node-flat-db/file-sync synchronous file storage .

const flat = require('node-flat-db')
const storage = require('node-flat-db/file-sync')
 
const db = flat('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 node-flat-db/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 flat = require('node-flat-db').
const storage = require('node-flat-db/file-async')
 
const db = flat('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, node-flat-db/browser will add localStorage support.

const flat = require('node-flat-db')
const storage = require('node-flat-db/browser')
 
const db = flat('db', { storage })
 
db('users').push({ name: 'typicode' })
const user = db('users').find({ name: 'typicode' })

In-memory

For the best performance, use node-flat-db in-memory storage.

const flat = require('node-flat-db')
const db = flat()
 
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.

Compression

compresses 1000 record db from 77kb to 7kb

The best way to use node-flat-db if space constraint is an issue, use lzstring adapter

const flat = require('node-flat-db')
const storage = require('node-flat-db/file-compress-sync')
 
const db = flat('db', { storage })
 
db('users').push({ name: 'typicode' })
const user = db('users').find({ name: 'typicode' })

API

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

Creates a new database instance. Here are some examples:

flat()                                      // in-memory
flat('db.json', { storage: /* */ })         // persisted
flat('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('node-flat-db/file-sync')
 
// write-only
flat('db.json', {
  storage: { write: fileSync.write }
})
 
// read-only
flat('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
  }
}
 
flat(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, node-flat-db automatically calls it when database changes.

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

Guide

How to query

With node-flat-db, 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: 'flat!' })
  .assign({ title: 'hi!'})
  .value()

Remove posts.

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

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 node-flat-db, you have 2 options.

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

const db = flat('db.json')
 
db._.mixin(require('underscore-db'))
 
const postId = db('posts').insert({ title: 'flat!' }).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: 'flat!' }).id
const post = db('posts').find({ id: postId })

How to use custom format

By default, node-flat-db 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 node-flat-db to storage.read and storage.write methods.

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

const flat = require('node-flat-db')
const storage = require('node-flat-db/file-sync')
const bson = require('bson')
const BSON = new bson.BSONPure.BSON()
 
flat('db.bson', { storage, format: {
  serialize: BSON.serialize,
  deserialize: BSON.deserialize
}})
 
// Alternative ES2015 short syntax
const bson = require('bson')
const format = new bson.BSONPure.BSON()
flat('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 = flat('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

node-flat-db 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.

Benchmarks

npm install microtime

npm run benchmarks

License

MIT - Gabriel J. Csapo