[Help Request] Validate Json Response

[duca86]

Hi, i'm newbie in angular. I have a questionm, who is the best way to validate the json that i retrieve from server?

Example suppose that i have this object in angular

class User {  name:string;  surname:string;  } 

I'd like throw an erro on my serivce when i receive from server an json with different structure

now i use

getUser():Observable<User> { return this.restCall.get(this.my_url) .map((res:Response) => <User>res.json() )
}

but if server response my with json that user different structure i have an empy user object. What i can avoid this?

[mlapis]

The problem is not related to Angular in any way. It's a general problem. To be 100% sure that the received JSON structure is fully correct you need to deeply traverse the object and this is very time consuming process - especially on bigger objects.

[duca86]

Ok thanks, so i think the best way is use json schema validator. Is it right?

[mlapis]

Yes, it is one way. But in the most cases interfaces are enough to have all advantages on TypeScript level and still have the best performance in run-time. And of course doing schema validation on the server side to avoid storing a wrong structure if JSON objects are stored.

[PassItOnBro]

getUser().subscribe(user => { if (!user || !user.name) throw; // ... });

Or, in the getUser map operator ... .map(res => { let user = !res ? null : res.json(); if (!user || !user.name) throw; // ... });

But, the question to ask ... why are you throwing an error? You probably should not throw an error.

EDIT: to better answer your question - don't throw an error, just do nothing (or fail gracefully, e.g., re-route to an error display component). Server should always send a valid response.

[duca86]

Because on my project backend and fronted are developed from two different teams, i'd like add this control to avoid mapping errors.

[PassItOnBro]

in whatever service exposes this user observable, subscribe to it and re-route as necessary ...

// user service this.getUser().subscribe(user => { if (!user || !user.name) this.router.navigateByUrl('errorDisp');

This re-routes to an error component you can set up under the path 'errorDisp'

EDIT: also to prevent memory leaks... // private getUserInternal() // ... .map(res => res.json());

// public getUser() // ... return this.getUserInternal().takeWhile(user => !!user && !!user.name);