Firebase Databaseでパスにuidを含めたユーザ権限周りをFirestoreでやるには

// BaseModel.ts

export default abstract class BaseModel {
    // ドキュメントオーナーのID
    readonly userID: string;

    // ドキュメントのID
    id: string | null;

    // ドキュメントの作成･更新日時
    timestamp: Date;

    constructor(userID: string, timestamp: Date) {
        this.userID = userID;
        this.timestamp = timestamp;
    }

    // Firestoreに保存するとき用
    abstract toJSON(): Object;
}

// ToDoModel.ts

import BaseModel from './BaseModel';

export default class ToDoModel extends BaseModel {
    // タイトル
    title: string;
    
    // ToDoが完了したかどうか
    completed: boolean = false;

    constructor(userID: string, title: string, timestamp: Date) {
        super(userID, timestamp);

        this.title = title;
    }

    toJSON(): Object {
        // NOTICE: idはfirestore上で自動で割り振られるのでわざわざデータとして格納しなくてよい
        return {
            userID: this.userID,
            title: this.title,
            completed: this.completed,
            timestamp: this.timestamp,
        };
    }
}

// database.rules.json

{
    "rules": {
        "todos": {
            "$uid": {
                ".read": "$uid === auth.uid",
                ".write": "$uid === auth.uid"
            }
        }
    }
}

// firestore.rules

service cloud.firestore {
    match /databases/{database}/documents {
        match /todos/{todoID} {
            allow read, write: if get(/databases/$(database)/documents/todos/$(todoID)).userID == request.auth.uid;
        }
    }
}

// index.ts

import * as firebase from "firebase";
import 'firebase/firestore';

import ToDoModel from './ToDoModel';

const frConfig = {
    apiKey: "<API_KEY>",
    authDomain: "<PROJECT_ID>.firebaseapp.com",
    databaseURL: "https://<DATABASE_NAME>.firebaseio.com",
    storageBucket: "<BUCKET>.appspot.com",
};

const firebaseApp = firebase.initializeApp(frConfig);

let rtdb: firebase.database.Database;
let frStore: firebase.firestore.Firestore;
let uid: string;

async function setup():Promise<void> {
    try {
        const user = await firebaseApp.auth().signInAnonymously();
        uid = user.uid;
        rtdb = firebaseApp.database();
        frStore = firebase.firestore(firebaseApp);
        return Promise.resolve();
    } catch (e) {
        return Promise.reject(e);
    }
}

async function rtdbCreate(): Promise<ToDoModel> {
    const key = rtdb.ref(`todos/${uid}`).push().key;

    const todoDoc = new ToDoModel(uid, '🍣をたくさんたべる (๑•̀ㅂ•́)و✧', new Date());
    todoDoc.id = key;

    const updates: { [key: string]: any } = {};
    updates[`todos/${uid}/${key}`] = todoDoc.toJSON();

    try {
        await rtdb.ref().update(updates);
    } catch (e) {
        return Promise.reject(e);
    }
    
    return Promise.resolve(todoDoc);
}

async function firestoreCreate(): Promise<ToDoModel> {
    const todoDoc = new ToDoModel(uid, '🍣をたくさんたべる (๑•̀ㅂ•́)و✧', new Date());

    try {
        const todoDocRef = await frStore.collection('todos').add(todoDoc.toJSON());
        todoDoc.id = todoDocRef.id;
    } catch (e) {
        return Promise.reject(e);
    }

    return Promise.resolve(todoDoc);
}

async function main() {
    await setup();
    
    console.log('uid: ', uid);

    const result1 = await rtdbCreate();
    console.log(result1);

    const result2 = await firestoreCreate();
    console.log(result2);
}

main();