Firebase 概述（BaaS）

Firebase谷歌的一款应用后台服务。借助Firebase，应用开发者们可以快速搭建应用后台。

产品

1. Firebase (realtime) database: Manage JSON documents + Real-time syncing data between users and devices
2. Firebase (cloud) storage: Store images, photos, videos
3. Firebase (user) authentication: Support sign in using Google, Facebook

使用

1. Create a Firebase account: first use Google account,then go to Firebase console: https://console.firebase.google.com/
2. Click on “Add project” to create a Firebase project
3. Add Firebase to your web app
4. any other interesting operation …

关于 Realtime database

• Data in JSON(Javascript Object Notation) format JSON-review
• When creating a real-time database, we should open up the access to allow us to read and write the data.
• There are some difference between storing style from JSON file and Firebase real-time database
  1. JSON文件中的array元素在Realtime database下以object的形式存在，object对应的key为数组元素的索引
  2. JSON文件可以保存value为null的键值对，Realtime database则会忽略这一对键值对
     

Firebase REST API

关于RESTful API

REST：Representation State Transfer，表现层状态转移
一句话解释的话就是:通过URL定位资源，用HTTP动词（GET, POST, PUT, DELETE)描述操作从而用来实现前后端数据传输的协议。

命令行进行http数据传输：curl

For command operation, it’s convenient to use curl (Command line tool for data transfer)
curl详细使用：https://itbilu.com/linux/man/4yZ9qH_7X.html
注意，curl大小写敏感，请求的命令参数均为大写字符

curl例子 - CRUD

PUT & POST (C), GET (R), PATCH (U) ,DELETE (D)

JSON tree:
{
  "firstName": "John",
  "lastName": "Smith",
  "isMarried": false,
  "age": 25,
  "height_cm": 167.6,
  "address": {
    "streetAddress": "22nd Street",
    "city": "New York",
    "state": "NY",
    "postalCode": "10021-3100"
  },
  "phoneNumbers": [
    {
      "type": "home",
      "number": "212 555-1234"
    },
    {
      "type": "office",
      "number": "646 555-4567",
      "xyz": null
    }
  ],
  "children": [],
  "spouse": null,
  "scores": [8.5, 9, 7, 10]
}

GET: get the specific resource

$ curl -X GET 'https://rest-apidemo.firebaseio.com/address/city.json'   return: "New York"%  
-X   可以省略 直接 curl GET url; GET  可以省略 直接 curl url

$ curl 'https://rest-apidemo.firebaseio.com/phoneNumbers/0.json' #refer to arr element by index
return:{"number":"212 555-1234","type":"home"}%  

PUT: write a given value (e.g., “Mary”) to a specify node (e.g., “spouse”)

Add if node not exists (could add embedded nodes) - 添加数据
Overwrite if node already has value               - 重写数据

$ curl -X PUT 'https://rest-apidemo.firebaseio.com/spouse.json' -d '"Mary"'  # 注意引号

#This will add a new node "country" (assuming it does not exist yet) 
#and a child of this node with key "province" and content: {"name": "Anhui"}
$ curl -X PUT 'https://rest-apidemo.firebaseio.com/country/province.json' -d '{"name": "Anhui"}' 
$ curl -X PUT 'https://rest-apidemo.firebaseio.com/country.json' -d '{"province": {"name": "Anhui"}}'

POST: add new value to a given node

Automatically generates a new key & then stores the value for the new key
由于对于添加的数据，其自动生成一个key，所以保证不会重写数据(In contrast, PUT will simply overwrite the key)
 
$ curl -X POST 'https://rest-apidemo.firebaseio.com/country.json' -d '{"province": {"name": "Anhui"}}'
$ curl -X POST 'https://rest-apidemo.firebaseio.com/country.json' -d  '"Anhui"'

PATCH: upsert a value to a given node

Performs the update if value already exists  -更新节点
Otherwise, it inserts the new value          -插入新节点
PATCH本质上是一个深度搜索符合节点的条件进行更新或者添加)

curl -X PATCH 'https://rest-apidemo.firebaseio.com/country.json' -d '{"province": {"name": "Hubei"}}'


好处:相比于PUT（对于已经存在的节点进行全局的修改），本质上来说PATCH实现的是对该节点的局部更新
注意:当需要更新的节点没有子节点（仅仅是一个key-value格式），无法使用PATCH，因为 -d 参数后需要传入键值对的格式
curl -X PATCH 'https://rest-apidemo.firebaseio.com/spouse.json' -d '"Sam"' # fail
{
  "error" : "Invalid data; couldn't parse JSON object. Are you sending a JSON object with valid key names?"
}
curl -X PUT 'https://rest-apidemo.firebaseio.com/spouse.json' -d '"Sam"' # success

DELETE: delete a node

curl -X DELETE 'https://rest-apidemo.firebaseio.com/spouse.json'

从数据增加、减少上对PUT、PATCH和POST进行比较

PUT可能造成数据的增加（添加新节点下的value）和减少（overwrite整个节点导致其内嵌的节点被删除）；
PATCH可能造成数据的增加（添加新节点下的value)和减少（update节点的用更少的数据去取代原先的数据）
POST一定会造成数据的增加（因为会自动加上key）；

data querying by RESful API

• orderBy=”$key”
• orderBy=”“
• orderBy=”$value” 需要在Realtime database的Rules先声明
• startAt/endAt
• equalTo
• limitToFirst/limitToLast

Specified in database rules:
https://firebase.google.com/docs/database/security/indexing-data

curl -X GET 'https://rest-apidemo.firebaseio.com/scores.json?orderBy="$key"&equalTo="1"'
curl -X GET 'https://rest-apidemo.firebaseio.com/scores.json?orderBy="$key"&startAt="1"'
curl -X GET 'https://rest-apidemo.firebaseio.com/scores.json?orderBy="$value"'

Orders ascendingly:
null -> false ->true -> number -> string -> object

REST API in Python

import requests

url = 'xxxx'
data = 'xxx'

requests.get(url) 
requests.put(url, data)
requests.patch(url, data)
requests.delete(url)
requests.post(url, data)