FirebaseObjectObservable 的更新方法交替更新 DOM 和 Firebase 数据库

Question

FirebbaseObjectObservable 的更新方法交替更新 DOM 和 Firebase 数据库。

 ngOnInit() {
    //Get Posts from posts service
    this.subscription = this.service.getCandidates()
      .subscribe(response => {
        this.candidates = response;
      })
  }

  vote(candidate){
    this.service.vote(candidate)
      .update({votes: candidate.votes++});
  }

  ngOnDestroy(){
    this.subscription.unsubscribe();
  }

服务来源

   export class PollService {

  constructor(private http: Http, private db: AngularFireDatabase) {

   }

  getCandidates(){
    //Get Candidates from Firebase and Return an observable
    return this.db.list('/candidates');
  }

  vote(candidate) {
    //Update the no. of votes corresponding to the candidate id
    return this.db.object('/candidates/' + candidate.$key)
  }
}

每当我第一次调用投票函数时，它会更新 DOM 但实际上不会更新数据库，下次我调用此函数时，它会更新数据库但不会更新 DOM。

我正在使用 Angular 5.2.0、Firebase 4.2.0。这是我的 package.json 文件

    {
  "name": "random-proj",
  "version": "0.0.0",
  "license": "MIT",
  "scripts": {
    "ng": "ng",
    "start": "ng serve",
    "build": "ng build --prod",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e"
  },
  "private": true,
  "dependencies": {
    "@angular/animations": "^5.2.0",
    "@angular/common": "^5.2.0",
    "@angular/compiler": "^5.2.0",
    "@angular/core": "^5.2.0",
    "@angular/forms": "^5.2.0",
    "@angular/http": "^5.2.0",
    "@angular/platform-browser": "^5.2.0",
    "@angular/platform-browser-dynamic": "^5.2.0",
    "@angular/router": "^5.2.0",
    "angular-crypto-js": "^1.0.7",
    "angularfire2": "^4.0.0-rc.1",
    "bootstrap": "^4.1.1",
    "core-js": "^2.4.1",
    "firebase": "^4.2.0",
    "rxjs": "^5.5.6",
    "sha.js": "^2.4.11",
    "zone.js": "^0.8.19"
  },
  "devDependencies": {
    "@angular/cli": "1.6.6",
    "@angular/compiler-cli": "^5.2.0",
    "@angular/language-service": "^5.2.0",
    "@types/jasmine": "~2.8.3",
    "@types/jasminewd2": "~2.0.2",
    "@types/node": "~6.0.60",
    "codelyzer": "^4.0.1",
    "jasmine-core": "~2.8.0",
    "jasmine-spec-reporter": "~4.2.1",
    "karma": "~2.0.0",
    "karma-chrome-launcher": "~2.2.0",
    "karma-coverage-istanbul-reporter": "^1.2.1",
    "karma-jasmine": "~1.1.0",
    "karma-jasmine-html-reporter": "^0.2.2",
    "protractor": "~5.1.2",
    "ts-node": "~4.1.0",
    "tslint": "~5.9.1",
    "typescript": "~2.5.3"
  }
}

Answer 1

（发现问题，想把它放在这里以防其他人将来遇到类似的问题）

将 candidate.votes++ 替换为 ++candidate.votes 使其按预期工作。在变量后面加上++，先把相同的数存入数据库，然后增加candidate.votes

的本地值

FirebaseObjectObservable 的更新方法交替更新 DOM 和 Firebase 数据库

Update method for the FirebaseObjectObservable alternatively updates DOM and the Firebase Database

firebase

typescript

firebase-realtime-database

angularfire2

angular