angular - 仅运行一次订阅

我只需要运行一次。但它的作用是无限的。你能告诉我怎么避免吗？
这是video of that issue：
TS

async loginWithGoogle(): Promise<void> {
    try {
      const result = await this.afAuth.auth.signInWithPopup(new firebase.auth.GoogleAuthProvider());
      const userId: string = result.additionalUserInfo.profile.id;
      const userProfile: AngularFirestoreDocument<UserProfile> = this.fireStore.doc(`userProfile/${userId}`);
      const userProfiles: AngularFirestoreCollection<UserProfile> = this.fireStore.collection('userProfile/', ref => ref.where('email', '==', result.additionalUserInfo.profile.email));
      const userProfiles$: Observable<UserProfile[]> = userProfiles.valueChanges();

      userProfiles$.subscribe(async res => { //problem is here
        if (res.length == 0) {
          await userProfile.set({
            id: userId,
            email: result.additionalUserInfo.profile.email,
            creationTime: moment().format(),
            lastSignInTime: moment().format()
          });
        } else {
          await userProfile.update({
            lastSignInTime: moment().format()
          });
        }
      });
    }
    catch (err) {
      console.log(err);
    }
  }

我试图将其转换为下面这样的userProfiles$.subscribe(async res => {。但没有区别。也许我做错了？

 userProfiles$.map(async res => {
        if (res.length == 0) {
          await userProfile.set({
            id: userId, email: result.additionalUserInfo.profile.email,
            creationTime: moment().format(),
            lastSignInTime: moment().format()
          });
        }
      }).toPromise();

版本：

 "typescript": "2.4.2"
 "rxjs": "5.5.2",

最佳答案

承诺方式：

userProfiles$.toPromise().then((res) => {
   if (res.length == 0) {
      await userProfile.set({
         id: userId, email: result.additionalUserInfo.profile.email,
         creationTime: moment().format(),
         lastSignInTime: moment().format()
      });
   }
}).catch(err => {
   // handle error
});

首先将其转换为promise，然后通过.then()方法收听它，等待解决的promise。
可观察。采取（1）

userProfiles$.take(1).subscribe(async res => { //problem is here
        if (res.length == 0) {
          await userProfile.set({
            id: userId,
            email: result.additionalUserInfo.profile.email,
            creationTime: moment().format(),
            lastSignInTime: moment().format()
          });
        } else {
          await userProfile.update({
            lastSignInTime: moment().format()
          });
        }
      });

注意不要忘记从rxjs操作符导入toPromise方法，对于toPromise您还应该从rxjs导入take方法

关于angular - 仅运行一次订阅，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/47718919/