Parsing Dynamic Json into a Map in Angular

Question

I use the http client of Angular to retrieve data from an API. I define DTOs using typescript interfaces. One of the endpoints returns a json object which has dynamic keys which I would like to have mapped into a Map. I tried various things.

v1

export interface ItemDistribution {
  id: number;
  distribution: Map<string, number>; // I don't know the keys beforehand
}

v2

interface Distribution {
   [key: string]: number;
}

export interface ItemDistribution {
  id: number;
  distribution: Distribution; // I don't know the keys beforehand
}

But, if I call the backend with http.get<ItemDistribution>(myUrl) the result gets parsed into a JavaScript object instead. I know that I could use Object.entries(...) on an object, but is it possible to get a Map directly?

GreyBeardedGeek · Accepted Answer · 2020-04-09 00:20:44Z

The key thing to understand is that when you add a type to an Angular HttpClient call, such as http.get<SomeObject>('http://api/some-end-point'), there's no mapping going on at all.

What you get back is an Object that is parsed from the JSON. That type that you specify is simply a cast, nothing actually gets converted. If the data in the JSON object doesn't match the type, there is no error or warning, it just doesn't conform to the type that your code expects, and you probably get a runtime error.

This is useful for simple objects, where the properties are limited to strings and numbers and arrays of strings, numbers, and arrays. If you have something more complex, like a Map, you need to convert that yourself from the JSON object.

So, no, you can't get a Map from the JSON object returned by your HttpClient call - you'll need to do that with Object.keys() or Object.entries() or something of the sort.

Collectives™ on Stack Overflow

Parsing Dynamic Json into a Map in Angular

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related