title: How to trigger again HttpGet request in Angular 6?
body: <p>I'm using <code>combineLatest</code> to merge data from <code>websocket</code> and <code>database</code> into one object. Each time the <code>websocket</code> sends data my data are refreshing. Although I'd like to refresh data at page manually also by pressing the button. Unfortunately <code>combineLatest</code> isn't detect that I made <code>HttpGet</code> request to get newest data.</p>
  
  <pre><code>export class ShowTestDataComponent implements OnInit {
    stockData: RootObject;
  
    private stocksData$: WebSocketSubject&lt;MessageEvent&gt;;
    private stocksResources$: Observable&lt;DbObject[]&gt;;
  
    constructor(private stockService: StockService, private webSocketService: WebSocketServiceService) {
      this.stocksData$ = this.webSocketService.connect();
      this.stocksResources$ = this.stockService.getStocksResources();
    }
  
    buyStock(code, quantityToBuy): void {
      const dto: DbObject = {
        code: code,
        quantity: quantityToBuy
      };
  
      this.stockService.buyStock(dto).pipe(
        mergeMap(() =&gt; this.stockService.getStocksResources())
      ).subscribe((res) =&gt; this.stocksResources$ = of(res));    
    }
  
    prepareStockData(): void {
      combineLatest(
        this.stocksData$,
        this.stocksResources$,
        (stockData: RootObject, stockResources: DbObject[]) =&gt; ({
          stockData,
          stockResources
        })
      ).subscribe((pair) =&gt; {
        this.stockData = JSON.parse(pair.stockData.data);
  
        this.stockData.Items.forEach(item =&gt; {
          item.Quantity = pair.stockResources.find(d =&gt; d.code === item.Code).quantity;
        });
      });
    }
  
    ngOnInit() {
      this.prepareStockData();
    }
  }
  </code></pre>
  
  <p>So as you can see If I'll press <code>BUY</code> on UI then method <code>buyStock</code> will be executed and there are executing <code>this.stockService.buyStock(dto)</code> to change data in DB, and then <code>this.stockService.getStocksResources()</code> to refresh data from DB. Everything works, data are changed but data isn't refreshing (comibneLatest isn't detect any message from <code>stocksResources$</code></p>
  
  <p>Here is my service, I think that problem is in componenet though.</p>
  
  <pre><code>export class StockService {
    apiUrl = "http://localhost:5001/api/values";
    constructor(private http: HttpClient) { }
  
    getStocksResources(): Observable&lt;DbObject[]&gt; {
      return this.http.get&lt;DbObject[]&gt;(this.apiUrl + "/stocks");
    }
  
    buyStock(data: DbObject){
      return this.http.post&lt;DbObject&gt;(this.apiUrl + "/quantity", data);
    }
  }
  </code></pre>