Angular Material Data Table component is not live streaming

Question

I'm using Angular Material Data Table in my project. The table is rendering with data

My problem is that I can't update automatically the view when I add new data to the database, every time I should refresh my page.

According to Cdk-table and after reading this tutorial I tried to add live data streaming that to table:

Here's my logique :

import { Component, OnInit } from "@angular/core";
import { MatTableDataSource } from "@angular/material";
import { AjoutprojService } from "../ajoutproj.service";
import { NouveauProjet } from "../models/nouveau-projet";
import { Observable } from "rxjs/Observable";
import 'rxjs/add/observable/merge';
import { DataSource } from "@angular/cdk/collections";



@Component({
  selector: "app-liste-projets",
  templateUrl: "./liste-projets.component.html",
  styleUrls: ["./liste-projets.component.css"]
})
export class ListeProjetsComponent implements OnInit {
  constructor( private ajoutProj: AjoutprojService  ) {}
  nouveauProjet: NouveauProjet[];
  nouveauProjet2: NouveauProjet[];

  stateExression: string = "inactive";

  ngOnInit() {}

  displayedColumns = ["Nom projet", "Lead Projet", "effectif"];
  dataSource = new UserDataSource(this.ajoutProj);
  applyFilter(filterValue: string) {
    filterValue = filterValue.trim(); // Remove whitespace
    filterValue = filterValue.toLowerCase(); // MatTableDataSource defaults to lowercase matches
    //this.dataSource.filter = filterValue;
  }

}
export class UserDataSource extends DataSource<any> {
  constructor(private ajoutProj: AjoutprojService) {
    super();
  }


/*returns an observable that emits an array of data. 
Whenever the data source emits data to this stream, the table will render an update.*/

  connect(): Observable<NouveauProjet[]> {
    return this.ajoutProj.getAllProj();
  }
  disconnect() {}
}

Here's my service

getAllProj(): Observable<NouveauProjet[]> {
  return this.http.get<NouveauProjet[]>(
    "http://127.0.0.1:8081/api/proj/projets"
  );
}

ajoutProj.getAllProj() service is getting right data. but view is not live updating.

Answer 1

HttpClient doesn't stream. You're getting your data only once.

Answer 2

First you'd need a realtime database / backend solution, then you need to connect to that via websocket and listen to changes in the database.

Some frameworks / libraries that I like and package both the client- and serverside of the equation, and make the whole thing a lot easier:

Fireloop - built on top of Loopback 3 on nodejs, provides Angular SDK creation, ie. same models and APIs on client as on server. Typescript, Observables all the way. It's just awesome.

Firebase - "backendless", totally different way of thinking about a "server" from any REST scheme you might be used to.

Meteor - a monolithic framework, probably also very far from what you're used to.

Of course there's always another (very inefficient) way: Poll your DB every X seconds for changes.

import {Observable} from 'rxjs/Observable';
import 'rxjs/add/operator/switchMap';
export class UserDataSource extends DataSource<any> {
  constructor(private ajoutProj: AjoutprojService) {
    super();
  }

  connect(): Observable<NouveauProjet[]> {
    const initialDelay = 0; // Time to wait before first poll, after the table has connected to this DataSource
    const period = 10000; // Polling period in milliseconds
    return Observable.timer(initialDelay, period)
        .switchMap(() => this.ajoutProj.getAllProj());
  }
  disconnect() {}
}