Display Data in Angular Material Table

Question

I'm struggling with the Angular mat-table library. I got an app with a Node.js backend and an Angular frontend. The node app provides data from a MySQL database in JSON.

Now I want to display this data in a mat-table. I have logged the data in the console, which allows me to see that the data is actually retrieved but just not displayed.

However, the HTML table is empty:

This is my Angular component:

component.html

<table mat-table [dataSource]="dataSource" class="mat-elevation-z8 demo-table">
  <ng-container matColumnDef="id">
    <th mat-header-cell *matHeaderCellDef>ID</th>
    <td mat-cell *matCellDef="let element">{{element.id}}</td>
  </ng-container>
  <ng-container matColumnDef="name">
    <th mat-header-cell *matHeaderCellDef>Name</th>
    <td mat-cell *matCellDef="let element">{{element.name}}</td>
  </ng-container>
  <ng-container matColumnDef="pop">
    <th mat-header-cell *matHeaderCellDef>Population</th>
    <td mat-cell *matCellDef="let element">{{element.population}}</td>
  </ng-container>


  <tr mat-header-row *matHeaderRowDef="displayedColumns"></tr>
  <tr
      mat-row
      (click)="clickedRows.add(row)"
      [class.demo-row-is-clicked]="clickedRows.has(row)"
      *matRowDef="let row; columns: displayedColumns;"
  ></tr>
</table>

component.ts

import {Component, OnInit,ViewChild} from '@angular/core';
import { Player } from '../player';
import { PlayerService } from '../player.service';
import { MatTableDataSource } from '@angular/material/table';
import {MatPaginator} from '@angular/material/paginator';
import {MatSort, SortDirection} from '@angular/material/sort';

/**
 * @title Binding event handlers and properties to the table rows.
 */
@Component({
  selector: 'app-players',
  styleUrls: ['players.component.css'],
  templateUrl: 'players.component.html',
})
export class PlayersComponent implements OnInit {
  displayedColumns: string[] = ['id', 'name', 'pop'];
  dataSource = new MatTableDataSource<Player>();

  @ViewChild(MatPaginator, { static: true }) paginator!: MatPaginator;
  @ViewChild(MatSort, { static: true }) sort!: MatSort;

  constructor(private playerService:PlayerService) { }

  ngOnInit(): void {
    this.getPlayers();
  }

  getPlayers() {
    this.playerService.getPlayers().subscribe(players => {
      console.log(players);
      this.dataSource.data = players;
      this.dataSource.paginator = this.paginator;
      this.dataSource.sort = this.sort;
    });
  }
  clickedRows = new Set<Player>();
}

player.service.ts

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable, of } from 'rxjs';
import { Player } from './player';

@Injectable({
  providedIn: 'root'
})
export class PlayerService {

  constructor(private http: HttpClient) { }
  rootURL = '/api';
  getPlayers(): Observable<Player[]> {
    return this.http.get<Player[]>(this.rootURL+ '/players');
  }
}

Any ideas on this?

EDIT: Could it have something to do with how the array comes back from the API? In Node.js it is retrieved with sequelize and maybe it is the response?

// Get all Players
exports.findAll = (req, res) => {
    Player.findAll().then((players) => {
    // Send all players as response
    res.status(200).json({
      status: true,
      data: players,
    });
  });
};

Answer 1

Issue

The data returned based on the screenshot and Node.js API is not Player array, but it is an object with status and data properties.

{
  "status": 200,
  "data": [...]
}

This line expected that HTTP GET to receive Player array which is conflict with your data.

this.http.get<Player[]>(this.rootURL+ '/players');

Hence, it returns Observable with an empty array and your <mat-table> will not show the data.

---

Solution

Transform the data to Player array with map rxjs operator.

import { map } from 'rxjs';

getPlayers(): Observable<Player[]> {
  return this.http
    .get(this.rootURL+ '/players')
    .pipe(map((response: any) => response.data as Player[]));
}

Sample Solution on StackBlitz