Angular2 : Type 'Subscription' is not assignable to type

Question

I have created a very small application to fetch countries from a json file and bind it to dropdown.

countries.json

export class Country {
    id: number;
    name: string;
}

factory.service.ts

import { Injectable } from '@angular/core';
import { Http, Response} from '@angular/http';
import { Observable } from 'rxjs/Observable';

import { Country } from './shared/country';

@Injectable()
export class FactoryService {
    private countryUrl = "app/data/countries.json";

    constructor(private http: Http) {

    }

    getCountry(): Observable<any> {
        return this.http.get(this.countryUrl)
            .map(this.extractData)
            .do(data => console.log("get Countries from json: " + JSON.stringify(data)))
            .catch(this.handleError);
    }

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

    private handleError(error: Response) {
        console.log(error);
        return Observable.throw(error.json().error || "500 internal server error");
    }
}

factory-form.component.ts

import { Component, OnInit } from '@angular/core';
import { NgForm } from '@angular/forms';

import { Factory } from './factory';
import { Country } from './shared/country';
import { FactoryService } from './factory.service';

@Component({
    moduleId: module.id,
    selector: 'factory-form',
    templateUrl: './factory-form.component.html',
    styleUrls: ['./factory-form.component.css'],
    providers: [FactoryService]
})
export class FactoryFormComponent implements OnInit{

    private model: Factory;
    countries: Country[];
    factoryStatuses;
    productTypes;
    risks;
    private errorMessage: string;
    private submitted = false;

    constructor(private factoryService: FactoryService) {

    }

    ngOnInit(): void {
        this.countries = this.factoryService.getCountry()
            .subscribe(countries => this.countries = countries,
            error => this.errorMessage = error);
    }

    onSubmit(): void {
        this.submitted = true;
    }}

factory-form.component.html snippet

<div class="col-lg-3">
            <select class="form-control" name="Country">
                <option *ngFor="let country of countries" [value]="country.id">{{country.name}}</option>
            </select>
        </div>

I am getting runtime error as below:

Error: Typescript found the following errors:
C:/Projects/ethical_resourcing/src/Ethos.Client/tmp/broccoli_type_script_compiler-input_base_path-kviWq7F3.tmp/0/src/app/factory/factory-form.component.ts (30, 9): Type 'Subscription' is not assignable to type 'Country[]'.
Property 'length' is missing in type 'Subscription'.
C:/Projects/ethical_resourcing/src/Ethos.Client/tmp/broccoli_type_script_compiler-input_base_path-kviWq7F3.tmp/0/src/app/factory/shared/country.ts (2, 15): ';' expected. at BroccoliTypeScriptCompiler._doIncrementalBuild (C:\Projects\ethical_resourcing\src\Ethos.Client\node_modules\angular-cli\lib\broccoli\broccoli-typescript.js:120:19) at BroccoliTypeScriptCompiler.build (C:\Projects\ethical_resourcing\src\Ethos.Client\node_modules\angular-cli\lib\broccoli\broccoli-typescript.js:43:10) at C:\Projects\ethical_resourcing\src\Ethos.Client\node_modules\angular-cli\node_modules\broccoli-caching-writer\index.js:152:21 at lib$rsvp$$internal$$tryCatch (C:\Projects\ethical_resourcing\src\Ethos.Client\node_modules\angular-cli\node_modules\rsvp\dist\rsvp.js:1036:16) at lib$rsvp$$internal$$invokeCallback (C:\Projects\ethical_resourcing\src\Ethos.Client\node_modules\angular-cli\node_modules\rsvp\dist\rsvp.js:1048:17) at lib$rsvp$$internal$$publish (C:\Projects\ethical_resourcing\src\Ethos.Client\node_modules\angular-cli\node_modules\rsvp\dist\rsvp.js:1019:11) at lib$rsvp$asap$$flush (C:\Projects\ethical_resourcing\src\Ethos.Client\node_modules\angular-cli\node_modules\rsvp\dist\rsvp.js:1198:9) at nextTickCallbackWith0Args (node.js:420:9) at process._tickCallback (node.js:349:13)

Now If I change the Type of Observable and countries to any then i get below error

ORIGINAL EXCEPTION: Cannot find a differ supporting object '[object Object]' of type 'object'. NgFor only supports binding to Iterables such as Arrays.

dfsq · Accepted Answer · 2016-07-09 18:42:16Z

17

Yes, the type must be an Observable and the you need to use async pipe to make ngFor happy:

*ngFor="let country of countries | async"

Or another option is to keep Country[] type but then subscribe and assign countries to array:

this.factoryService.getCountry() // note, removed this.countries = 
    .subscribe(
        countries => this.countries = countries,
        error => this.errorMessage = error
    );

answered Jul 9, 2016 at 18:42

dfsq

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3 Comments

Kamran Pervaiz Over a year ago

got this exception: Invalid argument '[object Object]' for pipe 'AsyncPipe'

Kamran Pervaiz Over a year ago

I removed the async pipe and tried your suggestion. voila it fixed the error. why this.countries was giving error? basically i was just following Pluralsight video and it was working for her. she was using beta but i am using rc.4. I wasted 3 hours :(

dfsq Over a year ago

I forgot to mention that is you use pipe then remove .subscribe(...) part: this.countries = this.factoryService.getCountry().error(...).

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