存在使用子级的Angularfire2过滤器数据

Question

I have my data like this .When I need to get data from question list I need to check if the current userid (loggedin user) exists in answeredStudents .If exists then that question need to hide from the user. Otherwise question will be shown in the list.

Here how i get questions:

getQuizesSeries()
  {
    let ref = this.afDB.list('questions').snapshotChanges()
    .map(changes =>{
      console.log(changes);
      return changes.map(c=> ({key:c.payload.key,...c.payload.val()}));
    });

    return ref;

  }

In my constructor I called that function like this:

  questions:Observable<any[]>;
  quizes:any;

  constructor(public navCtrl: NavController, public afDb:AngularFireDatabase ,public navParams: NavParams,public dataProvider:DataProvider) {
    this.quizes = this.dataProvider.getQuizesSeries();       
  }

and here is my html where its shows data:

<ion-list *ngFor="let quiz of quizes |async;let i = index;" >
    <ion-item (click)="passkey(quiz.key)">
        <p>{{quiz.name}}</p>
    </ion-item>
</ion-list>

Answer 1

You are going to have to grab the UID of the current student logged in.

eg

stduentID = //the id of the logged in user here

Then when you are creating the questions in the ion-list, you will have an ngIf checking the answeredStudents uid with the loggedIn user uid

<ion-list *ngFor="let quiz of quizes |async;let i = index;" >
    <ion-item (click)="passkey(quiz.key)" *ngIf="your logic here">
        <p>{{quiz.name}}</p>
    </ion-item>
</ion-list>

Answer 2

I tried to add a simple example with dummy data to solve this task. You need to use filter operator to filter out the questions that are already answered by the logged user.

In the below code I am checking whether the logged in user has already answered this question or not. If YES then skip this question else add this question to question list.

let questions = [
  {id: 1, desc: "desc1"},
  {id: 2, desc: "desc2"},
  {id: 3, desc: "desc3"}
];

let answeredStudents = [
  {id: 1, answered: [1]},
  {id: 2, answered: [1, 2]}
];

let loggedUserId = 1;

let questionsObs = Rx.Observable.from(questions);

function hasNotAnswered(id, question) {
  let user;
  answeredStudents.forEach(student => {
    if (student.id === id) {
      user = student;
    }
  });
  return !(user.answered.indexOf(question.id) > -1);
}

questionsObs.filter(question => hasNotAnswered(loggedUserId, question))
  .map(question => questionList.push(question));