ngFor not displaying arrays

Question

I have a search service:

getErros(start, end): FirebaseListObservable<any>{

this.hey = Rx.Observable.combineLatest(
  this.db.list('/erros/geral',{
          query: {
                  orderByChild: 'titulo',
                  limitToFirst:10,
                  startAt: start,
                  endAt: end
          }
      }),
  this.db.list('/erros/utilsst',{
          query: {
                  orderByChild: 'titulo',
                  limitToFirst:10,
                  startAt: start,
                  endAt: end
          }
      }),
  this.db.list('/erros/utilfac',{
          query: {
                  orderByChild: 'titulo',
                  limitToFirst:10,
                  startAt: start,
                  endAt: end
          }
      }),
      this.db.list('/erros/utilatas',{
          query: {
                  orderByChild: 'titulo',
                  limitToFirst:10,
                  startAt: start,
                  endAt: end
          }
      })

)

const errox = this.hey.flatMap(
    (([geral, utilsst, utilfac, utilatas]: [string, string, string, string]) => {
        let erros = [geral, utilsst,utilfac,utilatas];
        console.log(erros);
        return erros;
    } ))


return errox;

  }

And this is where it's called:

ngOnInit() {
    
    const errox = this.errosSvc.getErros(this.startAt, this.endAt)
            .subscribe(erros => this.erros = erros)
  }   

And it's only displaying one Array in the ngFor:

<tbody>
    <tr *ngFor="let erro of erros">
      <th id="butaoxx" class="col-md-1" style="text-align:center;" scope="row">
        <button id="butaox"  data-toggle="modal" attr.data-target="#{{erro.$key}}"
            class="panel panel-default" type="button" class="btn btn-primary btn-xs ">
            Abrir
        </button>
      </th>
      <td style="text-align:center;">{{erro?.titulo}}</td>
      <td style="text-align:center;">{{erro?.tema}}</td>
      <td  style="text-align:center;">{{erro?.subtema}}</td>
    </tr>
  </tbody>

I know the others Arrays and the search service is working because I implemented a console.log and the data appears right and the search works. The only problem is that the ngFor only displays data from the last Array which in this case is "utilatas".

Answer 1

you need flatten your array of array into array

    const errox = this.errosSvc.getErros(this.startAt, this.endAt) .subscribe(erros => {
 let flatten= [].concat.apply([], erros); 
console.log('flatten',flatten);
 this.erros = flatten})