Need a quick way to get a local database for a CLI, an Electron app, a small server or the browser?
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' })And access underlying database object any time.
db.object.postsNote: examples use ES2015 syntax for convenience, but you can use ES5 syntax too. For example:
var db = low('db.json', { storage: storage })Please note also that lowdb can only be run in one instance of Node, it doesn't support Cluster.
Using npm:
npm install lowdb --saveA standalone UMD build is also available on npmcdn for quick prototyping:
<script src="http://npmcdn.com/lowdb/dist/lowdb.min.js"></script>
<script>
var db = low() // in-memory database
var db = low('db', { storage: low.localStorage }) // enables localStorage
</script>- 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.
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.
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' })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(() => req.body)
})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' })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.
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/file-sync')
// 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.jsondb.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.jsonWith 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.
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!' })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 = uuid()
db('posts').push({ id: postId , title: 'low!' })
const post = db('posts').find({ id: postId })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 })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
}
}
})See changes for each version in the release notes.
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.
MIT - Typicode
React
Typescript
Django
Laravel
Facebook
Microsoft
Google
Alibaba
D3
Tencent