Encountering [object Object] when trying to map an HTTP response in Angular 2

Question

Encountering [object Object] when trying to map an HTTP response in Angular 2

When utilizing Observable map in angular 2, I encountered an issue where I am receiving an [object Object].

Below is the response object retrieved from the API service:

{
  "isSuccess": true,
  "message": "Connection Successfull",
  "data": [
    {
      "marketId": 1,
      "city": "san",
      "cityF": "san",
      "name": null,
      "nameF": "hello",
      "sortOrder": 1,
      "isActive": true
    },
    {
      "marketId": 2,
      "city": "san",
      "cityF": "san",
      "name": null,
      "nameF": "hello",
      "sortOrder": 1,
      "isActive": true
    },
    {
      "marketId": 3,
      "city": "san",
      "cityF": "san",
      "name": null,
      "nameF": "hello",
      "sortOrder": 1,
      "isActive": true
    },
    {
      "marketId": 4,
      "city": "san",
      "cityF": "san",
      "name": null,
      "nameF": "hello",
      "sortOrder": 1,
      "isActive": true
    }
  ],
  "exceptionErrorMessage": null,
  "errorCode": 0,
  "successMessage": null
}

Displayed below is the model I have constructed to correspond with the response:

export class MarketViewModel 
{
public isSuccess: boolean;
public message : string;
public successMessage : string;
public exceptionErrorMessage : string;
public errorCode: number;
public data: MarketListObject[];

}

export class MarketListObject 
{
    public marketId : number;
    public city: string;
    public cityF : string;
    public name : string;
    public nameF : string;
    public sortOrder : number;
    public isActive : boolean; 
}

The following is a snippet of the service class utilized to make the HTTP call and map the response:

import { Headers, RequestOptions } from '@angular/http';
import { Router, ActivatedRoute, Params } from '@angular/router';
import { MarketViewModel} from "../ViewModel/Market.ViewModel";
import { Injectable }     from '@angular/core';
import { Http, Response } from '@angular/http';
import {Observable} from 'rxjs/Rx';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/catch';

@Injectable()
export class DashBoardService {
    private MarketUrl = "DashBoard/GetMarketList";
    private ResponseData: any;

    constructor(private http: Http, private router: Router, private  marketModel : MarketViewModel) {}

    public GetMarketListCall() :Observable<MarketViewModel> {
         return this.http.get(this.MarketUrl).map(this.extractData)
                    .catch(this.handleError);
    } 

    private extractData(res: Response) {
        let body = res.json();
        console.log("Body Data = "+body.data);
        return body.data || { };
    }

Shown here is the Component.ts file responsible for invoking Service.ts:

import { Component } from '@angular/core';
import { MarketViewModel} from "../ViewModel/Market.ViewModel";
import { DashBoardService} from "../Service/DashBoard.Service";
import { Observable } from 'rxjs/Observable';

 @Component({
     selector: 'Market-app',
    templateUrl: 'DashBoard/MarketListView',
    providers: [DashBoardService, MarketViewModel]
 })

export class MarketComponent {
  constructor(private DashBoardservice: DashBoardService, private  marketModel : MarketViewModel) {
   }

ngOnInit() {
        this.DashBoardservice.GetMarketListCall().subscribe(
                               data => {this.marketModel = data;
                                    console.log("this"+this.marketModel); }, 
                                err => {console.log(err);});
}
}

I am currently facing an issue where the console output displays [object Object]. Can you help me identify what might be causing this error?

angular typescript asp.net-core angular-services

Answer 1

Answer №1

If you're encountering an issue with your extractData function where you require the response to match your MarketViewModel, then consider removing the data from the method. In cases where there is no response, ensure that an empty object is returned:

private extractData(res: Response) {
  let body = res.json();
  return body || {};
}

A few things to keep in mind:

There's no need to inject the MarketViewModel in the constructor of your Service and MarketComponent.
Declare a variable called marketModel within your component to utilize this.marketModel.
In your component, you've defined the method ngOnInit, but implementation is missing.

During testing, if your app functions correctly:

getMarketListCall(): Observable<MarketViewModel>{
    return this.http.get('theUrl')
        .map(res => res.json()) // or utilize 'extractData'
        // .catch(this.handleError);
}

Your component:

marketmodel: MarketViewModel

ngOnInit() {
    this.DashBoarservice.GetMarketListCall()
       .subscribe(data => {
          this.marketModel = data;
        },
        err => { console.log(err); 
    });
}

In your view, remember to wrap your html content within an if-statement due to asynchronous data retrieval:

For example:

<div *ngIf="marketModel"> <!-- Here! -->
  <h2>MarketModel Message: {{marketModel.message}}</h2>
  <div *ngFor="let data of marketModel.data">Id: {{data.marketId}} </div>
</div><br>

While the current code may work effectively, it doesn't explicitly cast the response to instances of your classes. If you wish to perform this casting, I recommend checking out this helpful link with valuable insights: How do I cast a JSON object to a typescript class

Answer 2

If you're encountering an issue with your extractData function where you require the response to match your MarketViewModel, then consider removing the data from the method. In cases where there is no response, ensure that an empty object is returned:

private extractData(res: Response) {
  let body = res.json();
  return body || {};
}

A few things to keep in mind:

There's no need to inject the MarketViewModel in the constructor of your Service and MarketComponent.
Declare a variable called marketModel within your component to utilize this.marketModel.
In your component, you've defined the method ngOnInit, but implementation is missing.

During testing, if your app functions correctly:

getMarketListCall(): Observable<MarketViewModel>{
    return this.http.get('theUrl')
        .map(res => res.json()) // or utilize 'extractData'
        // .catch(this.handleError);
}

Your component:

marketmodel: MarketViewModel

ngOnInit() {
    this.DashBoarservice.GetMarketListCall()
       .subscribe(data => {
          this.marketModel = data;
        },
        err => { console.log(err); 
    });
}

In your view, remember to wrap your html content within an if-statement due to asynchronous data retrieval:

For example:

<div *ngIf="marketModel"> <!-- Here! -->
  <h2>MarketModel Message: {{marketModel.message}}</h2>
  <div *ngFor="let data of marketModel.data">Id: {{data.marketId}} </div>
</div><br>

While the current code may work effectively, it doesn't explicitly cast the response to instances of your classes. If you wish to perform this casting, I recommend checking out this helpful link with valuable insights: How do I cast a JSON object to a typescript class

Answer 3

Answer №2

In order to make the necessary changes, modify your DashBoardService so that it returns an array of MarketListObject as observable instead of MarketViewModel:

@Injectable()
export class DashBoardService {
  private MarketUrl = "DashBoard/GetMarketList";
  private ResponseData: any;

  constructor(private http: Http, private router: Router, private  marketModel : MarketViewModel) {}

  public GetMarketListCall() :Observable<MarketListObject[]> {
     return this.http.get(this.MarketUrl).map(this.extractData)
                .catch(this.handleError);
  } 

  private extractData(res: Response) {
    let body = res.json();
    console.log("Body Data = "+body.data);
    return body.data || [];
  }
}

Furthermore, you no longer need to include MarketViewModel in the providers list of MarketComponent. Remove MarketViewModel from the providers list and update your component as follows:

import { Component } from '@angular/core';
import { DashBoardService} from "../Service/DashBoard.Service";
import { Observable } from 'rxjs/Observable';

@Component({
  selector: 'Market-app',
  templateUrl: 'DashBoard/MarketListView',
  providers: [DashBoardService]
})
export class MarketComponent {

  public marketList: any[];

  constructor(private dashBoardservice: DashBoardService) {
  }

  ngOnInit() {
    this.dashBoardservice.GetMarketListCall().subscribe((data) => { 
      this.marketList = data;
      console.log("this" + this.marketList);
    },(err) => {
      console.log(err);
    });
  }
}

Answer 4

In order to make the necessary changes, modify your DashBoardService so that it returns an array of MarketListObject as observable instead of MarketViewModel:

@Injectable()
export class DashBoardService {
  private MarketUrl = "DashBoard/GetMarketList";
  private ResponseData: any;

  constructor(private http: Http, private router: Router, private  marketModel : MarketViewModel) {}

  public GetMarketListCall() :Observable<MarketListObject[]> {
     return this.http.get(this.MarketUrl).map(this.extractData)
                .catch(this.handleError);
  } 

  private extractData(res: Response) {
    let body = res.json();
    console.log("Body Data = "+body.data);
    return body.data || [];
  }
}

Furthermore, you no longer need to include MarketViewModel in the providers list of MarketComponent. Remove MarketViewModel from the providers list and update your component as follows:

import { Component } from '@angular/core';
import { DashBoardService} from "../Service/DashBoard.Service";
import { Observable } from 'rxjs/Observable';

@Component({
  selector: 'Market-app',
  templateUrl: 'DashBoard/MarketListView',
  providers: [DashBoardService]
})
export class MarketComponent {

  public marketList: any[];

  constructor(private dashBoardservice: DashBoardService) {
  }

  ngOnInit() {
    this.dashBoardservice.GetMarketListCall().subscribe((data) => { 
      this.marketList = data;
      console.log("this" + this.marketList);
    },(err) => {
      console.log(err);
    });
  }
}

Encountering [object Object] when trying to map an HTTP response in Angular 2

Answer №1

Answer №2

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