angularwakanda

Calling a service in a service and returning async result?


Using Angular 5. A component calls a service. This service must call another service before making a server call. I am not able to get the result asynchronously in the component. I use ellipses for brevity below.

Component:

...
import { SystemOnlineService } from '../services/system-online.service';
...
constructor(private sys: SystemOnlineService) {
    sys.getStatus()
    .then(result => {
        console.log(result);
    });
}

SystemOnlineService:

import { Injectable } from '@angular/core';
import { Wakanda } from './wakanda.service';
import 'rxjs/add/operator/toPromise';
...
getStatus() {

    this.wakanda.getCatalog()
    .then((ds) => {
        this.ds = ds;
        this.ds.Rpc_reportObjectHelper.isMySystemUp()
        .then(statusArr => {
            return statusArr;
        });
    });
}

The component throws this error about the sys.getStatus() call:

Uncaught (in promise): TypeError: Cannot read property 'then' of undefined

If I console.log(sys.getStatus());, it logs undefined.

I think I am just missing something about how to properly make async calls.


Solution

  • the 'getStatus()' should return a promise. Now, it is returning nothing. You can rewrite this way:

    getStatus() {
    
      return new Promise( resolve => {
        this.wakanda.getCatalog()
        .then((ds) => {
            this.ds = ds;
            return this.ds.Rpc_reportObjectHelper.isMySystemUp()
            .then(statusArr => {
                resolve(statusArr);
            });
        });
      })
    }
    

    Or, event better, if this block of code does not have any toher logic, you can remove unecessary code (using arrow functions):

    getStatus() {
      return new Promise( resolve => {
        this.wakanda.getCatalog()
        .then( ds => ds.Rpc_reportObjectHelper.isMySystemUp().then( data => resolve(data)) )
      })
    }