# LowDB
**Repository Path**: kisshua/LowDB
## Basic Information
- **Project Name**: LowDB
- **Description**: LowDB 是一个简单的基于文件的 JSON 数据库引擎
- **Primary Language**: JavaScript
- **License**: MIT
- **Default Branch**: main
- **Homepage**: https://www.oschina.net/p/lowdb
- **GVP Project**: No
## Statistics
- **Stars**: 0
- **Forks**: 4
- **Created**: 2022-09-09
- **Last Updated**: 2022-09-09
## Categories & Tags
**Categories**: Uncategorized
**Tags**: None
## README
# lowdb [](https://www.npmjs.org/package/lowdb) [](https://github.com/typicode/lowdb/actions/workflows/node.js.yml)
> Simple to use local JSON database. Powered by plain JavaScript 🦉
```js
// Edit db.json content using plain JS
db.data
.posts
.push({ id: 1, title: 'lowdb is awesome' })
// Save to file
db.write()
```
```js
// db.json
{
"posts": [
{ "id": 1, "title": "lowdb is awesome" }
]
}
```
If you like lowdb, see also [xv](https://github.com/typicode/xv) (test runner) and [steno](https://github.com/typicode/steno) (fast file writer).
## Sponsors
[Become a sponsor and have your company logo here](https://github.com/sponsors/typicode).
Please help me build OSS 👉 [GitHub Sponsors](https://github.com/sponsors/typicode)
## Features
- __Lightweight__
- __Minimalist__
- __TypeScript__
- __plain JS__
- Atomic write
- Hackable:
- Change storage, file format (JSON, YAML, ...) or add encryption via [adapters](#adapters)
- Add lodash, ramda, ... for super powers!
## Install
```sh
npm install lowdb
```
## Usage
_Lowdb 3 is a pure ESM package. If you're having trouble importing it in your project, please [read this](https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c)._
```js
import { join, dirname } from 'path'
import { Low, JSONFile } from 'lowdb'
import { fileURLToPath } from 'url'
const __dirname = dirname(fileURLToPath(import.meta.url));
// Use JSON file for storage
const file = join(__dirname, 'db.json')
const adapter = new JSONFile(file)
const db = new Low(adapter)
// Read data from JSON file, this will set db.data content
await db.read()
// If file.json doesn't exist, db.data will be null
// Set default data
// db.data = db.data || { posts: [] } // Node < v15.x
db.data ||= { posts: [] } // Node >= 15.x
// Create and query items using plain JS
db.data.posts.push('hello world')
const firstPost = db.data.posts[0]
// Alternatively, you can also use this syntax if you prefer
const { posts } = db.data
posts.push('hello world')
// Finally write db.data content to file
await db.write()
```
```js
// db.json
{
"posts": [ "hello world" ]
}
```
### TypeScript
You can use TypeScript to type check your data.
```ts
type Data = {
words: string[]
}
const adapter = new JSONFile('db.json')
const db = new Low(adapter)
db.data
.words
.push('foo') // ✅
db.data
.words
.push(1) // ❌
```
### Lodash
You can also add lodash or other utility libraries to improve lowdb.
```ts
import lodash from 'lodash'
type Post = {
id: number;
title: string;
}
type Data = {
posts: Post[]
}
// Extend Low class with a new `chain` field
class LowWithLodash extends Low {
chain: lodash.ExpChain = lodash.chain(this).get('data')
}
const adapter = new JSONFile('db.json')
const db = new LowWithLodash(adapter)
await db.read()
// Instead of db.data use db.chain to access lodash API
const post = db.chain
.get('posts')
.find({ id: 1 })
.value() // Important: value() must be called to execute chain
```
### More examples
For CLI, server and browser usage, see [`examples/`](/examples) directory.
## API
### Classes
Lowdb has two classes (for asynchronous and synchronous adapters).
#### `new Low(adapter)`
```js
import { Low, JSONFile } from 'lowdb'
const db = new Low(new JSONFile('file.json'))
await db.read()
await db.write()
```
#### `new LowSync(adapterSync)`
```js
import { LowSync, JSONFileSync } from 'lowdb'
const db = new LowSync(new JSONFileSync('file.json'))
db.read()
db.write()
```
### Methods
#### `db.read()`
Calls `adapter.read()` and sets `db.data`.
**Note:** `JSONFile` and `JSONFileSync` adapters will set `db.data` to `null` if file doesn't exist.
```js
db.data // === null
db.read()
db.data // !== null
```
#### `db.write()`
Calls `adapter.write(db.data)`.
```js
db.data = { posts: [] }
db.write() // file.json will be { posts: [] }
db.data = {}
db.write() // file.json will be {}
```
### Properties
#### `db.data`
Holds your db content. If you're using the adapters coming with lowdb, it can be any type supported by [`JSON.stringify`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify).
For example:
```js
db.data = 'string'
db.data = [1, 2, 3]
db.data = { key: 'value' }
```
## Adapters
### Lowdb adapters
#### `JSONFile` `JSONFileSync`
Adapters for reading and writing JSON files.
```js
new Low(new JSONFile(filename))
new LowSync(new JSONFileSync(filename))
```
#### `Memory` `MemorySync`
In-memory adapters. Useful for speeding up unit tests.
```js
new Low(new Memory())
new LowSync(new MemorySync())
```
#### `LocalStorage`
Synchronous adapter for `window.localStorage`.
```js
new LowSync(new LocalStorage(name))
```
#### `TextFile` `TextFileSync`
Adapters for reading and writing text. Useful for creating custom adapters.
### Third-party adapters
If you've published an adapter for lowdb, feel free to create a PR to add it here.
### Writing your own adapter
You may want to create an adapter to write `db.data` to YAML, XML, encrypt data, a remote storage, ...
An adapter is a simple class that just needs to expose two methods:
```js
class AsyncAdapter {
read() { /* ... */ } // should return Promise
write(data) { /* ... */ } // should return Promise
}
class SyncAdapter {
read() { /* ... */ } // should return data
write(data) { /* ... */ } // should return nothing
}
```
For example, let's say you have some async storage and want to create an adapter for it:
```js
import { api } from './AsyncStorage'
class CustomAsyncAdapter {
// Optional: your adapter can take arguments
constructor(args) {
// ...
}
async read() {
const data = await api.read()
return data
}
async write(data) {
await api.write(data)
}
}
const adapter = new CustomAsyncAdapter()
const db = new Low(adapter)
```
See [`src/adapters/`](src/adapters) for more examples.
#### Custom serialization
To create an adapter for another format than JSON, you can use `TextFile` or `TextFileSync`.
For example:
```js
import { Adapter, Low, TextFile } from 'lowdb'
import YAML from 'yaml'
class YAMLFile {
constructor(filename) {
this.adapter = new TextFile(filename)
}
async read() {
const data = await this.adapter.read()
if (data === null) {
return null
} else {
return YAML.parse(data)
}
}
write(obj) {
return this.adapter.write(YAML.stringify(obj))
}
}
const adapter = new YAMLFile('file.yaml')
const db = new Low(adapter)
```
## Limits
Lowdb doesn't support Node's cluster module.
If you have large JavaScript objects (`~10-100MB`) you may hit some performance issues. This is because whenever you call `db.write`, the whole `db.data` is serialized using `JSON.stringify` and written to storage.
Depending on your use case, this can be fine or not. It can be mitigated by doing batch operations and calling `db.write` only when you need it.
If you plan to scale, it's highly recommended to use databases like PostgreSQL or MongoDB instead.