Angular2 Typescript Convert Firebase JSON to Object

Question

The following Firebase code returns a list of products in json:

firebase.database().ref('/products/').once('value');

In Angular2, what's the best way to convert this json to an array of product objects?

e.g. Array of product objects.

products: Product[];

e.g. Product object.

export class Product {
    public id: string;
    public name: string;
}

I see many references to Angular 2 http.get that use map e.g. https://angular.io/docs/ts/latest/guide/server-communication.html#!#sts=More%20fun%20with%20Observables

getHeroes (): Observable<Hero[]> {
    return this.http.get(this.heroesUrl)
                    .map(this.extractData)
                    .catch(this.handleError);
  }

But I don't understand how to use map or some other typescript convention to do this.

Updated question to clarify what an array/list of product objects might look like. — Matthew
– Matthew, Commented Jul 9, 2016 at 15:18
...Just found an answer here: stackoverflow.com/a/41752653/7467098 — Luciano Liranço
– Luciano Liranço, Commented Jan 25, 2017 at 4:07

Matthew · Accepted Answer · 2016-08-12 16:20:46Z

1

The following code works but feels sub-optimal. The get function returns an Observable array of products that can be bound to ngFor. Note the use of the Firebase once function. This is really a data snapshot and not a data stream.

this.products = get();

template:

<div *ngFor="let product of products">
    <div>{{product?.id}}</div>
</div>

function:

get(): Observable<Wishlist[]> {

    return Observable.fromPromise(
        firebase.database().ref('products').once('value')
    ).flatMap(snapshot => {
        let objects = snapshot.val();
        let products: Array<Product> = new Array();
        for (let key in objects) {
            let object = objects[key];
            let product: Product = new Product(key, object.name);
            products.push(product);
        }
        return Observable.of(products);
    })
}

answered Aug 12, 2016 at 16:20

Matthew

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Comments

Thierry Templier · Accepted Answer · 2016-07-06 19:08:19Z

0

You could get data by registering a callback on once and call the val method on the provided parameter:

ref.once("value", (snap) => {
  var data = snap.val();
});

See this doc for more details:

https://www.firebase.com/docs/web/guide/retrieving-data.html

answered Jul 6, 2016 at 19:08

Thierry Templier

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1 Comment

Matthew Over a year ago

Understood, but how is this json mapped to an object?

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