angular4 error handling in service and controller

Question

I have the following question:

I have a http post request in a service. The request returns a object:

export interface IResponse<T> {
    Error:boolean
    ErrorMessage:string
    Data:T
}

If an error is generated in either php or mysql the boolean is set to true with a message. The request from the service:

searchPersons(personSearchObject:PersonSearchObject){
    //generate request here
    return this.http.post(Config.ServerUrl, "data="+ request, options)
    .map( (responseData) => {
        this.personResponse = responseData.json()
        if (!this.personResponse.Error){
            this.persons.next(this.personResponse.Data)
            return;
        } else {
            console.log(this.personResponse.ErrorMessage)
            return Observable.throw(new Error(this.personResponse.ErrorMessage))
        }
    })
}

The request is called from the controller:

 this.personSearchService.searchPersons(personSearchObject).subscribe(
                result => {},
                error => { 
                    console.log("There was an error");
            })
        }

Now the problem is that the error=> in the controller is only hit when for example the php backend is down, not when I throw the error from the service.

How can I notify the controller that there was an error in the response from the request?

Other question is can I simply leave out the result in the controller, and only catch the error?

Thanks,

Everything would be so much easier if your backend, instead of returning a response with status 200 success, but a body indicating that there was in fact an error, respected the HTTP standard and returned an actual error response, with status 500 internal error. Why don't you do that? — JB Nizet
– JB Nizet, Commented Nov 3, 2017 at 8:01

JB Nizet · Accepted Answer · 2017-11-03 08:17:58Z

1

You should definitely fix your backend, so that it returns actual error responses. But anyway, your code should rather be:

searchPersons(personSearchObject:PersonSearchObject) {
  return this.http.post(Config.ServerUrl, "data="+ request, options)
    .switchMap(response => {
      const personResponse = response.json()
      if (!personResponse.Error) {
        return Observable.of(personResponse.Data);
      } 
      else {
        return Observable.throw(new Error(personResponse.ErrorMessage));
      }
    });
}

Note that the Http service is deprecated. You should switch to HttpClient.

answered Nov 3, 2017 at 8:17

JB Nizet

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1 Comment

Maniac_1979 Over a year ago

Thank you for this. Exploring HTTPClient now, which raises another bunch of questions, but will continue to explore.

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