javascript – How to create a nested mat-table in a table with expandable rows using angular material-ThrowExceptions

Exception or error:

I have the below data

[
    {
        "_id": "c9d5ab1a",
        "subdomain": "wing",
        "domain": "aircraft",
        "part_id": "c9d5ab1a",
        "info.mimetype": "application/json",
        "info.dependent": "parent",
        "nested": [
            {
                "domain": "aircraft",
                "_id": "c1859902",
                "info.mimetype": "image/jpeg",
                "info.dependent": "c9d5ab1a",
                "part_id": "c1859902",
                "subdomain": "tail"
            }
        ]
    },
    {
        "_id": "1b0b0a26",
        "subdomain": "fuel",
        "domain": "aircraft",
        "part_id": "1b0b0a26",
        "info.mimetype": "image/jpeg",
        "info.dependent": "no_parent"
    }
]

Here if "info.dependent": "parent" then it is nested and if "info.dependent": "no_parent" then it does not have a child. I tried to create a dynamic table but I am stuck on how to make it collapsible/expandable with a nested table.
Here is my code on stackblitz.

<mat-table class=" mat-elevation-z8" [dataSource]="dataSource">

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

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

</mat-table>

.ts

public data = [
    {
        "_id": "c9d5ab1a",
        "subdomain": "wing",
        "domain": "aircraft",
        "part_id": "c9d5ab1a",
        "info.mimetype": "application/json",
        "info.dependent": "parent",
        "nested": [
            {
                "domain": "aircraft",
                "_id": "c1859902",
                "info.mimetype": "image/jpeg",
                "info.dependent": "c9d5ab1a",
                "part_id": "c1859902",
                "subdomain": "tail"
            }
        ]
    },
    {
        "_id": "1b0b0a26",
        "subdomain": "fuel",
        "domain": "aircraft",
        "part_id": "1b0b0a26",
        "info.mimetype": "image/jpeg",
        "info.dependent": "no_parent"
    }
];

dataSource = new MatTableDataSource([]);
displayedColumns = ['_id', 'subdomain', 'domain', 'part_id', 'info.mimetype', 'info.dependent'];

constructor(){
    this.displayedColumns = this.displayedColumns;
    this.dataSource = new MatTableDataSource(this.data);
}

Required format :–>
nested table

The nested format is like below

row 1 –> _id ,subdomain,domain,info.dependent

When we click on that particular row, then it has to expand and display the nested data in a table with the column names and row data.

"nested": [
    {
        "domain": "aircraft",
        "_id": "c1859902",
        "info.mimetype": "image/jpeg",
        "info.dependent": "c9d5ab1a",
        "part_id": "c1859902",
        "subdomain": "tail"
    }
]
How to solve:

Note: For those who want to skip the lengthy explanation, here is the StackBlitz example.

What you actually want is to create a nested mat-table where all the nested tables are sortable and can be filtered through as well.

Firstly, since you need to use filtering and sorting in your nested table, you need to create a new MatTableDataSource for it. This can be done initially when you create the main dataSource in the ngOnInit like below.

usersData: User[] = [];

USERS.forEach(user => {
    if (user.addresses && Array.isArray(user.addresses) && user.addresses.length) {
        this.usersData = [...this.usersData, { ...user, addresses: new MatTableDataSource(user.addresses) }];
    } else {
        this.usersData = [...this.usersData, user];
    }
});
this.dataSource = new MatTableDataSource(this.usersData);

From the expandable rows example in the docs, we can see how to create an expandable row. In the expandable row, we will now have a table along with the Filter input. We will add some conditions so that the row is expandable only if there are addresses present.

<div class="example-element-detail" *ngIf="element.addresses?.data.length"
    [@detailExpand]="element == expandedElement ? 'expanded' : 'collapsed'">
    <div class="inner-table mat-elevation-z8" *ngIf="expandedElement">
        <mat-form-field>
            <input matInput (keyup)="applyFilter($event.target.value)" placeholder="Filter">
        </mat-form-field>
        <table #innerTables mat-table #innerSort="matSort" [dataSource]="element.addresses" matSort>
            <ng-container matColumnDef="{{innerColumn}}" *ngFor="let innerColumn of innerDisplayedColumns">
                <th mat-header-cell *matHeaderCellDef mat-sort-header> {{innerColumn}} </th>
                <td mat-cell *matCellDef="let element"> {{element[innerColumn]}} </td>
            </ng-container>
            <tr mat-header-row *matHeaderRowDef="innerDisplayedColumns"></tr>
            <tr mat-row *matRowDef="let row; columns: innerDisplayedColumns;"></tr>
        </table>
    </div>
</div>

Now that the row expands only if there are nested elements, we need to get rid of the hover for the users which have no addresses

Here is the CSS responsible for adding a background-color on hover

tr.example-element-row:not(.example-expanded-row):hover {
    background: #777;
}

So we just need to add the example-element-row class to our row if the row has an address. If it has no address, the row should not be clickable and there should not be a hover which indicates to the user that the row is in fact not clickable.

<tr mat-row *matRowDef="let element; columns: columnsToDisplay;" 
    [class.example-element-row]="element.addresses?.data.length"
    [class.example-expanded-row]="expandedElement === element"
    (click)="toggleRow(element)">
</tr>

In toggleRow, we will define the logic for what happens when you click a row in the template. We will also implement sort when the user clicks on the row in this function.

@ViewChildren('innerSort') innerSort: QueryList<MatSort>;

toggleRow(element: User) {
    element.addresses && (element.addresses as MatTableDataSource<Address>).data.length ? (this.expandedElement = this.expandedElement === element ? null : element) : null;
    this.cd.detectChanges();
    this.innerTables.forEach((table, index) => (table.dataSource as MatTableDataSource<Address>).sort = this.innerSort.toArray()[index]);
}

Finally, we need to define the applyFilter function so the nested tables can be filtered.

@ViewChildren('innerTables') innerTables: QueryList<MatTable<Address>>;

applyFilter(filterValue: string) {
    this.innerTables.forEach((table, index) => (table.dataSource as MatTableDataSource<Address>).filter = filterValue.trim().toLowerCase());
}

Here is a working example on StackBlitz.

###

Looking at the examples from the docs especially the one with the expandable row:

  • You are missing the multiTemplateDataRows directive in the <mat-table>
  • The @detailExpand trigger is missing

Here is the example from the docs with your data

Edit (regarding the comment)

Here is how you can get the dynamic columns:

Add this to your component

  getKeys(object): string[] {
    return Object.keys(object);
  }

use the method in the template (template updated according to the attached details screen and the note about the multiple elements under the nested key):

<div class="example-element-descriptions">
    <div *ngFor="let nested of element['nested']"
         class="example-element-description">
        <div *ngIf="element['info.dependent'] === 'parent'">
            <div class="example-element-description__header">
                <div class="example-element-description__cell"
                     *ngFor="let key of getKeys(nested)">{{key}}</div>
            </div>
            <div class="example-element-description__content">
                <div class="example-element-description__cell"
                     *ngFor="let key of getKeys(nested)">{{element[key]}}
                </div>
            </div>
        </div>
        <div *ngIf="element['info.dependent'] === 'no_parent'">no parent</div>
    </div>
</div>

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