Display a nested object in a dynamic material table template

Question

I want to display weight.name in the table. I was able to do it with transforming the data. However, I do not want to manipulate the data in any shape. I tried changing weightto weight.name in the row template ( displayedColumns ) but got back no data at all.

App.component.html

<table mat-table [dataSource]="dataSource">
  <ng-container *ngFor="let col of displayedColumns" [matColumnDef]="col">
    <th mat-header-cell *matHeaderCellDef> {{col}} </th>
    <td mat-cell *matCellDef="let element"> {{element[col]}} </td>
  </ng-container>

  <tr mat-header-row *matHeaderRowDef="displayedColumns"></tr>
  <tr mat-row *matRowDef="let row; columns: displayedColumns;"></tr>
</table>

App.component.ts

import { Component } from '@angular/core';

export interface PeriodicElement {
  name: string;
  position: number;
  weight: any;
  symbol: string;
}

const ELEMENT_DATA: PeriodicElement[] = [
  {position: 1, name: 'Hydrogen', weight: {name: 5.55}, symbol: 'H'},
  {position: 2, name: 'Helium', weight: {name: 5.55}, symbol: 'He'},
  {position: 3, name: 'Lithium', weight: {name: 5.55}, symbol: 'Li'},
  {position: 4, name: 'Beryllium', weight: {name: 5.55}, symbol: 'Be'},
  {position: 5, name: 'Boron', weight: {name: 5.55}, symbol: 'B'},
  {position: 6, name: 'Carbon', weight: {name: 5.55}, symbol: 'C'},
  {position: 7, name: 'Nitrogen', weight: {name: 5.55}, symbol: 'N'},
  {position: 8, name: 'Oxygen', weight: {name: 5.55}, symbol: 'O'},
  {position: 9, name: 'Fluorine', weight: {name: 5.55}, symbol: 'F'},
  {position: 10, name: 'Neon', weight: {name: 5.55}, symbol: 'Ne'},
];

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: [ './app.component.css' ]
})
export class AppComponent  {
  displayedColumns: string[] = ['position', 'name', 'weight', 'symbol'];
  dataSource = ELEMENT_DATA;
}

This is the stackblitz link for reference. https://stackblitz.com/edit/angular-mat-table-dynamic-columns-x36dvr?file=src%2Fapp%2Fapp.component.ts

Answer 1

Your issue is that you are displaying the weight column as row[col] or rowInstance['weight'] which displays the toString() of the weight object resulting in [object object].

1. modify your table template to something like:

   <table mat-table [dataSource]="dataSource">
        <ng-container matColumnDef="position"> 
            <mat-header-cell *matHeaderCellDef> Position </mat-header-cell>
            <mat-cell *matCellDef="let row">{{row.position}}</mat-cell>
        </ng-container> 
        <ng-container matColumnDef="name"> 
            <mat-header-cell *matHeaderCellDef> Name </mat-header-cell>
            <mat-cell *matCellDef="let row">{{row.name}}</mat-cell>
        </ng-container>
        <ng-container matColumnDef="weightName"> 
            <mat-header-cell *matHeaderCellDef> Weight </mat-header-cell>
            <mat-cell *matCellDef="let row">{{row.weight.name}}</mat-cell>
        </ng-container>
        <ng-container matColumnDef="symbol"> 
            <mat-header-cell *matHeaderCellDef> Symbol </mat-header-cell>
            <mat-cell *matCellDef="let row">{{row.symbol}}</mat-cell>
        </ng-container>
   
        <mat-header-row *matHeaderRowDef="displayedColumns">
        </mat-header-row>
        <mat-row *matRowDef="let row; columns: displayedColumns;">
        </mat-row>
    </table>
   

and in your ts file, modify the display columns to:

  `displayedColumns: string[] = ['position', 'name', 'weightName', 'symbol'];`

https://stackblitz.com/edit/angular-mat-table-dynamic-columns-w7do4c?file=src/app/app.component.html

2. transform/flatten your data model upstream to be something like the following and leave your template unchanged.

   [{position: 1, name: 'Hydrogen', weightName: 5.55, symbol: 'H'},...]