Angular 6 - Common Mistakes in Retrieving Data from Observables

I initially used the example from Heroes as a guide, but with a different API method - mine is post instead of get.

This is the Interface I have:

export interface IContasMae {
codEstab: string;
codProduto: string;
desContaMae: string;
codRep: number;
numQuantidade: number;
numValVenda: number;
numValMedio: number;}

In the service, I've implemented the following method:

  getContasMae() : Observable<IContasMae[]> {
    if (this.getUser()) {   
      return this.http.post<IContasMae[]>(`${environment.api_url}/getContasMae`,''); 
    }
  }

The property 'contasMae' in the component is defined as:

export class PanelDashboardComponent implements OnInit {
  public contasMae: IContasMae[];

(Referencing the above interface)

To call the method in the component, it's done like this:

this.service.getContasMae().subscribe(contasMae => 
  {
    console.log('Observable:',contasMae);
    this.contasMae = contasMae;
  });
console.log('Result:',this.contasMae);
} 

The console log for the Observable shows the data retrieved, but when checking 'this.contasMae', it returns undefined.

What could be causing this issue? How can I store the result in 'this.contasMae' successfully?

If anyone has any ideas or solutions, your help would be greatly appreciated!

Thank you in advance.

Answer №1

When working with this.contasMae, the approach you take will depend on your specific needs.

If you intend to display this data in a template within a component, you can achieve this simply by doing the following:

<div>{{ contasMae | async }}</div>

async is an Angular pipe designed to handle asynchronous data within your views.

To iterate through the list in your view, you can use the following code snippet:

<li *ngFor="let item of contasMae | async" [value]="item">{{item}}</li>

Keep in mind that Observables operate asynchronously. Therefore, in your example, the console.log() function may execute before the Observable has resolved and emitted a value.

You can find additional examples and information about the async pipe here: https://angular.io/api/common/AsyncPipe

If you plan to utilize the value of this.contasMae within your component class, one method is to encapsulate any logic involving this instance variable inside a method in your component class.

For instance:

public ngOnInit() {
    this.service.getContasMae().subscribe(contasMae => 
    {
        console.log('Observable:',contasMae);
        this.contasMae = contasMae;
        doSomething();
    });
}

public doSomething() {
    console.log('Resultado:',this.contasMae);
}

In the above example, access to this.contasMae will only occur once a value has been emitted from your observable, resolving and assigning the result to this.contasMae.

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