npm install 'firebase-admin'

const admin = require("firebase-admin");
const firestore = require("firebase-admin/firestore");
const serviceAccount = require("./firebaseKey.json");

admin.initializeApp({
  credential: admin.credential.cert(serviceAccount)
});

const db = firestore.getFirestore();

module.exports = db ;

// firestore 에서 비밀키 생성하면 주는 파일 ./firebaseKey.json
{
  "type": "servt",
  "project_id": "osad9",
  "private_key_id": "5895f402ac2ccc05",
  "private_key": "6Jto",
  "client_email": "firebasafd9.com",
  "client_id": "10802113896883",
  "auth_uri": "ht.com",
  "token_uri": "<https://ogl>"
  "auth_provider_x509_cert_url": "https.com/s",
  "client_x509_cert_url": "<https://www.go40osam-2afd9.iam.gserviceaccount.com>"
}

CRUD

const fireDB = require('../db/firestoreCon.js');

//read
const userRef = await fireDB.collection(issueInfo.type).doc(issueInfo.subject).get();
// 없으면 userRef._fieldsProto === undefined

//create
await fireDB.collection("컬렉션이름").doc("문서이름").set("순수 자바스크립트 객체");

//update
const userRef = await db.collection("users").doc(id)
    .update({
      firstName: newFirstName
    });

//delete
db.collection("users").doc(req.params.id).delete();