Casting Response from HTTP Post to List of Typescript Objects

Question

I have a call to my web API already written. The API returns a list of objects serialized in JSON. I know that there are fairly reasonable ways to cast individual items from JSON to typescript objects, but I cant figure out a way to do this casting to make it return a list of a typescript object.

I need to cast to a typescript object as there is a function in the object I want to be able to run, but without casting the function does not exist.

Here is the code used to retrieve the JSON:

  findTrainPage(filter = '', sortOrder = 'desc', pageNumber = 0, pageSize = 15, departStart=null, departEnd=null, origStatusWhitelist=null): Observable<Train[]>
  {
    //retrieves a page of trains to display in the train list
    let url = AppUtils.backendApiUrl() + '/trainList/getPage';
    let requestBody = { 'filter': filter, 'sortOrder': sortOrder, 'pageNum': pageNumber, 'pageSize': pageSize, 'departStart': departStart, 'departEnd': departEnd, 'origStatusWhitelist': origStatusWhitelist };
    let options = new RequestOptions({ headers: AppUtils.commonHttpHeaders() });
    let headers = { headers: AppUtils.commonHttpHeaders() };
    return this.http.post(url, requestBody, headers).map(res => res.json()).catch(error => Observable.throw(error.json()));
  }

And here is the Train object I am trying to cast to:

export class Train implements TrainInterface
{
  trainGUID: string;
  trainSymbol: string;
  createTime: string; //Should be formatted as a date, SQL table uses smalldatetime
  departTime: string;
  origStatus: OriginalStatuses;
  badGUIDFlag: boolean;
  trips: Trip[];

  private _evalStatus: EvalStatuses;
  get evalStatus(): EvalStatuses
  {
    return this.trips.reduce((min, p) => p.evalStatus < min ? p.evalStatus : min, this.trips[0].evalStatus);
  }
}

I have looked at the following SO posts:

JSON to TypeScript class instance?

Angular2 HTTP GET - Cast response into full object

Supun Dharmarathne · Accepted Answer · 2018-06-07 06:34:41Z

0

Create a response wrapper class. This should match with the API response structure.

export declare class ResponseWrapper<T> {
    static SUCCESS: number;
     data: Array<T>;
}

Then map the response as follows.

 findTrainPage(filter = '', sortOrder = 'desc', pageNumber = 0, pageSize = 15, departStart = null, departEnd = null, origStatusWhitelist = null): Observable<any> {
//retrieves a page of trains to display in the train list
// let url = AppUtils.backendApiUrl() + '/trainList/getPage';
const url = 'assets/mockdata.json';
let requestBody = {
  'filter': filter,
  'sortOrder': sortOrder,
  'pageNum': pageNumber,
  'pageSize': pageSize,
  'departStart': departStart,
  'departEnd': departEnd,
  'origStatusWhitelist': origStatusWhitelist
};
let options = new RequestOptions();
return this.http.get(url)
           .map(res => res.json())
           .catch(error => Observable.throw(error.json()));

}

Usage :

trainList : Train[];

  constructor(private trainService: TrainService) {
    this.trainService.findTrainPage()
        .subscribe(data =>{
        const  resultsWrapper:ResponseWrapper<Train> = data;
        this.trainList = resultsWrapper.data;
        });
       //   error => this.errorMessage = error);
  }

Here is the tested source https://gitlab.com/supun/angular-stack-overflow-ref

edited Jun 7, 2018 at 6:34

answered Jun 6, 2018 at 9:05

Supun Dharmarathne

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2 Comments

DeceitfulEcho Over a year ago

I get the following error when trying to assign resultsWrapper in the usage case: "type any[] is not assignable to type ResponseWrapper<Train[]>. Property data is missing in type any[]."

Supun Dharmarathne Over a year ago

Please check my modified answer

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