Cannot convert http request to observable array Angular 2

Question

I've been following the Tour of Heroes chapter on http calls and am trying to implement something similar with a different API. However, I get the following error:

Cannot find a differ supporting object '[object Object]' of type 'Bond Street 1'. NgFor only supports binding to Iterables such as Arrays.

Any clues on why this is?

My service looks as follows and works when I console.log the result

  search(stationNumber: number): Observable<BikeStand[]> {
    return this.http.get(`APIURL${stationNumber}`)
      .map((b: Response) => {
        console.log(b.json() as BikeStand[])
        return b.json() as BikeStand[];
      });
  }

My component looks as follows

export class BikestandSearchComponent implements OnInit {

  bikestands: Observable<BikeStand[]>;
  private searchTerms = new Subject<number>();

  constructor(private bikestandSearchService: BikestandSearchService) { }

  search(term: number): void {
    this.searchTerms.next(term);
  }

  ngOnInit(): void {
    this.bikestands = this.searchTerms
      .debounceTime(300)
      .distinctUntilChanged()
      .switchMap(term => term ? this.bikestandSearchService.search(term) : Observable.of<BikeStand[]>([]))
      .catch(error => {
        console.log(error);
        return Observable.of<BikeStand[]>([])
      })
  }

And my view likes this

<div id="search-component">
  <h4>Bikestand search</h4>
  <input #searchBox id="search-box" (keyup)="search(searchBox.value)" />
  <div *ngFor="let bikestand of bikestands | async">{{bikestand.name}}</div>
</div>

My api for a given key looks as follow FYI

{
number: 1,
name: "Bond Street 1",
address: "Street",
position: {
lat: 55.340962,
lng: -6.3
},
banking: false,
bonus: false,
status: "OPEN",
contract_name: "City",
bike_stands: 29,
available_bike_stands: 19,
available_bikes: 10,
last_update: 1473356300000
}

Steven Luke · Accepted Answer · 2016-09-08 18:37:45Z

1

It looks like your service or HTTP request isn't actually sending an array, it is sending a single Object. For example, I ran this code:

import {Component, NgModule} from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'

@Component({
  selector: 'my-app',
  template: `
    <div>
      <h2>Hello {{name}}</h2>
      <p *ngFor="let bike of bikestand">{{bike.name}}</p>
    </div>
  `,
})
export class App {

  bikestand:any = {
    number: 1,
    name: "Bond Street 1",
    address: "Street",
    position: {
      lat: 55.340962,
      lng: -6.3
    },
    banking: false,
    bonus: false,
    status: "OPEN",
    contract_name: "City",
    bike_stands: 29,
    available_bike_stands: 19,
    available_bikes: 10,
    last_update: 1473356300000
  };

  constructor() {
    this.name = 'Angular2'
  }
}

@NgModule({
  imports: [ BrowserModule ],
  declarations: [ App ],
  bootstrap: [ App ]
})
export class AppModule {}`

And got the same error. But change bikestand to an actual array (by putting square brackets around it) and I get correct result.

answered Sep 8, 2016 at 18:37

Steven Luke

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2 Comments

user3642173 Over a year ago

Thanks both. As you mentioned changing return b.json() as BikeStand[]; to return [b.json()] as BikeStand[]; in my service fixes the problem. I'm surprised though that casting it as BikeStand[] doesn't automatically transform the output into an array

Steven Luke Over a year ago

Casting doesn't do a conversion, you are just telling TypeScript 'trust me, this method returns any but I know what is inside is Bikestand[], so please treat it like that.'

candidJ · Accepted Answer · 2016-09-08 18:30:08Z

1

as the error states, you are trying to iterate over an object using *ngFor rather than an array. the api you are using/returned is an object.

Check if console.log(b.json() as BikeStand[]) returns an objects which has some data property. if true then

return b.json().data instead .

we want to extract array out of the object to iterate over.

answered Sep 8, 2016 at 18:30

candidJ

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