Is it possible for Angular2 to map a lone JSON object?

Dealing with a JSON response that is a single object, rather than an array, can be tricky. Recently in my project, I encountered a situation where I needed to map and use such a response from an API to fill out a template. It seemed like a simple task at first, but turned out to be more challenging than anticipated.

Example of the JSON response:

{
        "id": 1,
        "name": "Acaeris",
    }
    

profile.service.ts

import { Injectable } from '@angular/core';
    import { Http, Response } from '@angular/http';
    import { Observable } from 'rxjs/Observable';
    import { Profile } from './profile';
    
    @Injectable()
    export class ProfileService {
        constructor(private http: Http) {}
    
        get(): Observable<Profile> {
            return this.http.get('assets/profile.json')
                .map(res => <Profile>res.json())
                .catch(this.handleError);
        }

        private handleError (error: any) {
            let errMsg = (error.message) ? error.message :
                error.status ? `${error.status} - ${error.statusText}` : 'Server error';
            console.error(errMsg);
            return Observable.throw(errMsg);
        }
    }
    

Answer №1

Seems like the expression {{profile.name}} is undefined when the page is rendered. To fix this, you can create a getter function like this:

get profileName(): string { return this.profile ? this.profile.name ? ''; }

You can then use {{profileName}} in your template or use ngIf like this:

<div *ngIf="profile">{{profile.name}}</div>

Another option, as suggested by drewmoore in the comment below, is to use a shorter version:

<div>{{profile?.name}}</div>

When dealing with arrays, the situation is similar - the array is undefined during the initial rendering. However, ngFor takes care of this and renders nothing initially. Once the async operation fetching 'profile items' is completed, the UI is rerendered with the correct values.

Answer №2

When using the map function, you will receive Observables that consist of a collection of elements. This operates in a similar manner to the map function used with arrays.

To address this issue, you can substitute any instances of Profile with Profile[] and utilize {{profile[0].name}}.

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