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

Question

I looked at similar questions, but none of them helped me. I am going to receive an object like the following:

[
  {
    "id": 1,
    "name": "Safa",
    "email": "[email protected]",
    "purpose": "thesis",
    "programme": "Software Engineering",
    "year": 2016,
    "language": "Estonian",
    "comments": "In need of correcting a dangling participle.",
    "status": "RECEIVED"
  },
  {
    "id": 2,
    "name": "Safa",
    "email": "[email protected]",
    "purpose": "thesis",
    "programme": "Software Engineering",
    "year": 2016,
    "language": "Estonian",
    "comments": "In need of correcting a dangling participle.",
    "status": "RECEIVED"
  },
  {
    "id": 3,
    "name": "Salman",
    "email": "[email protected]",
    "purpose": "thesis",
    "programme": "Software Engineering",
    "year": 2016,
    "language": "Estonian",
    "comments": "In need of correcting a dangling participle.",
    "status": "RECEIVED"
  }
]

and here is my http service to receive it:

getRequest(){
        return this._http.get("http://consultationwebserver.herokuapp.com/requests").map(res => res.json());
    }

and finally, in the i called the service in this way:

requests;
    constructor(private _http:requestService){}
    ngOnInit(){
        this.requests=this._http.getRequest().subscribe(res=>this.requests=res);
    }

Unfortunately, when the page loads it complains with:

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

So, what is going wrong with this code?

Answer 1

There you don't need to use this.requests= when you are making get call(then requests will have observable subscription). You will get a response in observable success so setting requests value in success make sense(which you are already doing).

this._http.getRequest().subscribe(res=>this.requests=res);

If it still shows an error related to type, add any/RelevantModel type on subscribe parameter object.

this._http.getRequest().subscribe(
  (res: any[]) => this.requests =res
);

Basically, *ngFor works for only iterable items like arrays. If you assign this.requests to have an object value, and you're trying to use *ngfor it will return this error.

For example, when you declare array like this.myArray = {} this problem will occur. It should be this.myArray = [].

Answer 2

Remove this.requests from

ngOnInit(){
  this.requests=this._http.getRequest().subscribe(res=>this.requests=res);
}

to

ngOnInit(){
  this._http.getRequest().subscribe(res=>this.requests=res);
}

this._http.getRequest() returns a subscription, not the response value. The response value is assigned by the callback passed to subscribe(...)

Answer 3

You can declare the books (on line 2) as an array:

title: any = 'List of books are represted in the bookstore';
books: any = []; 
constructor(private service:  AppService){
}

ngOnInit(){
  this.getBookDetails();
}

getBookDetails() {
    this.service.getBooks().subscribe(books => {
        this.books = books.json();
        console.log(this.books);
    });
}

Answer 4

My solution is create a Pipe for return the values array or propierties object

import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
  name: 'valueArray',
})
export class ValueArrayPipe implements PipeTransform {

  // El parametro object representa, los valores de las propiedades o indice
  transform(objects : any = []) {
    return Object.values(objects);
  }
}

The template Implement

<button ion-item *ngFor="let element of element_list | valueArray" >
    {{ element.any_property }}
</button>