Firebase Realtime DatabaseFirebase Realtime Database

// Firebase RTDB는 하나의 거대한 JSON 트리
{
  "users": {
    "uid123": {
      "name": "홍길동",
      "email": "hong@example.com",
      "lastSeen": 1704067200000
    }
  },
  "messages": {
    "chatRoom1": {
      "msg001": {
        "sender": "uid123",
        "text": "안녕하세요",
        "timestamp": 1704067200000
      }
    }
  }
}

import { initializeApp } from 'firebase/app';
import { getDatabase, ref, onValue, push, set, query, orderByChild, limitToLast } from 'firebase/database';

const app = initializeApp({ databaseURL: 'https://my-app.firebaseio.com' });
const db = getDatabase(app);

// 실시간 데이터 수신 (변경 시 자동 호출)
const messagesRef = ref(db, 'messages/chatRoom1');
const recentQuery = query(messagesRef, orderByChild('timestamp'), limitToLast(50));

onValue(recentQuery, (snapshot) => {
  const messages = [];
  snapshot.forEach((child) => {
    messages.push({ id: child.key, ...child.val() });
  });
  renderMessages(messages);
});

// 메시지 전송
async function sendMessage(text) {
  const newMsgRef = push(ref(db, 'messages/chatRoom1'));
  await set(newMsgRef, {
    sender: 'uid123',
    text,
    timestamp: Date.now()
  });
}

{
  "rules": {
    "users": {
      "$uid": {
        ".read": "$uid === auth.uid",
        ".write": "$uid === auth.uid"
      }
    },
    "messages": {
      "$roomId": {
        ".read": "auth != null",
        ".write": "auth != null",
        "$messageId": {
          ".validate": "newData.hasChildren(['sender','text','timestamp']) && newData.child('sender').val() === auth.uid"
        }
      }
    }
  }
}