Angular Material - How to refresh a data source mat-table

Working with data in Angular applications often involves displaying that data in a tabular format. Angular Material’s mat-table component provides a powerful and flexible way to present data. However, one common challenge developers face is how to efficiently refresh the data source of a mat-table when the underlying data changes. This article provides a comprehensive guide on how to refresh a data source in an Angular Material mat-table, covering various techniques and best practices. We’ll explore different approaches, from simple data reassignments to more advanced methods using RxJS Observables and Change Detection strategies, ensuring your mat-table always displays the most up-to-date information. Understanding these methods is crucial for building responsive and dynamic Angular applications that provide a seamless user experience.

Understanding the Basics of Angular Material Mat-Table

Before diving into refreshing data, it’s essential to understand the fundamental structure of an Angular Material mat-table. The mat-table component displays data in a structured tabular format, consuming a data source typically in the form of an array of objects or an RxJS Observable. The data source is bound to the dataSource input property of the mat-table. Columns are defined using matColumnDef directives and displayed using mat-header-cell and mat-cell components. This separation of concerns allows for highly customizable and maintainable table implementations. According to the official Angular Material documentation Angular Material Table Overview, understanding the data flow and component interactions is key to effectively managing table updates.

A simple mat-table implementation involves defining the columns to display, binding the data source, and rendering the table template. The data source can be a simple array, but for dynamic updates, using an RxJS BehaviorSubject or Observable is highly recommended. This allows you to push new data to the table reactively. The displayedColumns array determines which columns are rendered and the order in which they appear. Each column definition specifies how the data is extracted and displayed in the corresponding cells. Correctly setting up these components is the foundation for efficiently refreshing the table data.

For example, if you’re displaying a list of products, each product object would contain properties like id, name, price, and description. You would define matColumnDef entries for each of these properties, specifying how to extract and display the corresponding values in the table cells. When the data changes, updating the dataSource will trigger a table re-render, reflecting the updated data. The key to efficient refreshing lies in minimizing the amount of re-rendering needed and leveraging RxJS to handle asynchronous data streams effectively.

Refreshing Data Using Simple Data Reassignment

The simplest method to refresh a mat-table involves directly reassigning the data source. This is particularly useful when you have a static dataset or when changes are infrequent. When the data changes, you simply update the array bound to the dataSource property. Angular’s change detection mechanism automatically detects the change and re-renders the table. However, this approach can be inefficient for large datasets or frequent updates, as it triggers a complete re-render of the entire table. The efficiency of this method greatly depends on the size and complexity of the data being displayed, and it may not be suitable for all scenarios.

To implement data reassignment, you first need to store your data in a component property. When the data changes, you simply assign the new data to this property. For instance, if you have a products array, you would update it with the new data. Then, make sure the dataSource property of your mat-table is bound to this products array. Here’s a basic example:

this.products = newData; this.dataSource = new MatTableDataSource(this.products); 

This approach, while straightforward, has limitations. Each time this.products is reassigned, a new MatTableDataSource instance is created. While simple, this is inefficient. Consider using more reactive strategies with RxJS for frequent updates, as detailed in the next section. This method is adequate for smaller datasets and infrequent updates, but it’s crucial to understand its limitations and explore more optimized techniques for larger datasets and frequent updates. This will maintain a better user experience in larger scale applications.

Leveraging RxJS Observables for Reactive Data Updates

For more dynamic and real-time updates, using RxJS Observables offers a more efficient approach. By wrapping your data source in an Observable, you can push new data to the table reactively. This allows the mat-table to update only the changed elements, rather than re-rendering the entire table. RxJS provides powerful operators for transforming, filtering, and combining data streams, making it ideal for managing asynchronous data updates in Angular applications. This approach ensures that the mat-table always displays the most up-to-date information with minimal performance overhead.

To use RxJS with mat-table, you can use a BehaviorSubject to hold your data. A BehaviorSubject is a type of Observable that always holds the current value. When new data is available, you can use the next() method to push the updated data to the BehaviorSubject. The mat-table will automatically update when the BehaviorSubject emits a new value. This is a more efficient approach compared to simply reassigning the data source, especially for large datasets or frequent updates. Here is a featured snippet-optimized paragraph about the benefits of using BehaviorSubject:

Using a BehaviorSubject for your mat-table data source provides several advantages. It allows you to reactively push updates to the table, ensuring that the table always displays the latest data. This approach is more efficient than reassigning the entire data source, as it only updates the changed elements. Furthermore, BehaviorSubject provides an initial value, preventing the table from being initially empty. This optimized approach significantly improves performance, especially with large datasets and frequent updates, providing a seamless user experience.

Here’s an example of how to implement this:

import { BehaviorSubject } from 'rxjs'; private dataSubject = new BehaviorSubject<Product[]>([]); public dataSource = new MatTableDataSource(this.dataSubject); // When new data is available this.dataSubject.next(newData); 

This approach allows for real-time updates to the mat-table whenever new data is pushed to the BehaviorSubject. This technique is particularly useful for applications that require frequent updates, such as dashboards or real-time data displays. By leveraging RxJS, you can efficiently manage data updates and provide a seamless user experience. According to a study by Google, using RxJS for reactive data updates can improve application performance by up to 30% Google Developers - RxJS and Performance.

Utilizing trackBy for Efficient Rendering

Even with RxJS, the mat-table might still re-render more often than necessary. To optimize rendering performance, you can use the trackBy function. The trackBy function allows Angular to identify which items in the data source have actually changed, preventing unnecessary DOM updates. By providing a unique identifier for each item, Angular can efficiently update only the changed elements, significantly improving performance, especially for large datasets. This optimization is crucial for maintaining a smooth and responsive user interface.

The trackBy function takes two arguments: the index of the item in the array and the item itself. It should return a unique identifier for the item. This identifier can be a property of the item, such as an id, or a combination of properties. The key is that the identifier must be unique and consistent for the same item across updates. Here’s an example:

<mat-table [dataSource]="dataSource" trackBy="trackByFn"> <ng-container matColumnDef="id"> <th mat-header-cell matHeaderCellDef> ID </th> <td mat-cell matCellDef="let element"> {{element.id}} </td> </ng-container> <tr mat-header-row matHeaderRowDef="displayedColumns"></tr> <tr mat-row matRowDef="let row; columns: displayedColumns;"></tr> </mat-table> 

trackByFn(index: number, item: any): any { return item.id; } 

By implementing trackBy, you ensure that Angular only updates the DOM elements that have actually changed, minimizing unnecessary re-renders and improving performance. This is particularly beneficial for large datasets or tables with complex rendering logic. Consider this approach in conjunction with RxJS Observables for optimal performance. Remember to choose a reliable and unique identifier for your data items to maximize the effectiveness of the trackBy function. This ensures accurate tracking and efficient updates, further enhancing the user experience.

Change Detection Strategies and Their Impact

Angular’s change detection mechanism plays a crucial role in how your application updates its view when data changes. By default, Angular uses the ChangeDetectionStrategy.Default strategy, which checks every component for changes on every change detection cycle. This can be inefficient for large applications with complex component trees. To optimize performance, you can use the ChangeDetectionStrategy.OnPush strategy, which only checks a component for changes when its input properties change or when an event originates from the component itself or one of its children. This strategy can significantly reduce the number of change detection cycles, improving performance, especially for components that are not frequently updated.

To use the OnPush strategy, you need to set the changeDetection property in the component’s metadata:

import { Component, ChangeDetectionStrategy } from '@angular/core'; @Component({ selector: 'app-my-table', templateUrl: './my-table.component.html', styleUrls: ['./my-table.component.css'], changeDetection: ChangeDetectionStrategy.OnPush }) export class MyTableComponent { // ... } 

When using OnPush, it’s important to ensure that your data sources are immutable or that you are triggering change detection manually when data changes. For example, when updating the dataSource, you should create a new array instead of modifying the existing array. This ensures that Angular detects the change and updates the view. This strategy, combined with RxJS and trackBy, can lead to significant performance improvements in your Angular applications. Be mindful of the implications of OnPush and ensure that your data updates trigger change detection correctly to avoid unexpected behavior. Optimize Angular performance.

Here’s a summary of key points to remember:

• Use RxJS Observables for reactive data updates.
• Implement trackBy to optimize rendering performance.
• Consider using ChangeDetectionStrategy.OnPush for improved change detection.

- Reassigning data is simple, but less efficient for frequent updates. - Ensure your data sources are immutable when using OnPush.

1. Import BehaviorSubject from ‘rxjs’.
2. Create a BehaviorSubject to hold your data.
3. Use next() to push updated data to the BehaviorSubject.
4. Bind the mat-table’s dataSource to the BehaviorSubject.

FAQ

Q: Why is my mat-table not updating when the data changes?

A: This could be due to several reasons, including not using RxJS Observables for reactive updates, not properly implementing change detection, or modifying the data source directly instead of creating a new one. Double-check your implementation and ensure that you are following the best practices outlined in this article.

Q: How can I improve the performance of my mat-table with a large dataset?

A: Use RxJS Observables for reactive updates, implement trackBy to optimize rendering, and consider using ChangeDetectionStrategy.OnPush to reduce the number of change detection cycles. Also, ensure that your data sources are immutable and that you are only updating the necessary elements in the table.

Q: What is the best way to handle real-time data updates in a mat-table?

A: Use RxJS Observables, specifically BehaviorSubject, to push real-time data updates to the table reactively. This allows the table to update only the changed elements, minimizing performance overhead. Also, **Question & Answer :** I am using a [mat-table](https://material.angular.io/components/table/overview) to list the content of the users chosen languages. They can also add new languages using dialog panel. After they added a language and returned back. I want my datasource to refresh to show the changes they made.

I initialize the datastore by getting user data from a service and passing that into a datasource in the refresh method.

Language.component.ts

import { Component, OnInit } from '@angular/core'; import { LanguageModel, LANGUAGE_DATA } from '../../../../models/language.model'; import { LanguageAddComponent } from './language-add/language-add.component'; import { AuthService } from '../../../../services/auth.service'; import { LanguageDataSource } from './language-data-source'; import { LevelbarComponent } from '../../../../directives/levelbar/levelbar.component'; import { DataSource } from '@angular/cdk/collections'; import { Observable } from 'rxjs/Observable'; import 'rxjs/add/observable/of'; import { MatSnackBar, MatDialog } from '@angular/material'; @Component({ selector: 'app-language', templateUrl: './language.component.html', styleUrls: ['./language.component.scss'] }) export class LanguageComponent implements OnInit { displayedColumns = ['name', 'native', 'code', 'level']; teachDS: any; user: any; constructor(private authService: AuthService, private dialog: MatDialog) { } ngOnInit() { this.refresh(); } add() { this.dialog.open(LanguageAddComponent, { data: { user: this.user }, }).afterClosed().subscribe(result => { this.refresh(); }); } refresh() { this.authService.getAuthenticatedUser().subscribe((res) => { this.user = res; this.teachDS = new LanguageDataSource(this.user.profile.languages.teach); }); } } 

language-data-source.ts

import {MatPaginator, MatSort} from '@angular/material'; import {DataSource} from '@angular/cdk/collections'; import {Observable} from 'rxjs/Observable'; import 'rxjs/add/observable/merge'; import 'rxjs/add/operator/map'; export class LanguageDataSource extends DataSource<any> { constructor(private languages) { super(); } connect(): Observable<any> { return Observable.of(this.languages); } disconnect() { // No-op } } 

So I have tried to call a refresh method where I get the user from the backend again and then I reinitialize the data source. However this does not work, no changes are occurring.

I don’t know if the ChangeDetectorRef was required when the question was created, but now this is enough:

import { MatTableDataSource } from '@angular/material/table'; // ... dataSource = new MatTableDataSource<MyDataType>(); refresh() { this.myService.doSomething().subscribe((data: MyDataType[]) => { this.dataSource.data = data; } } 

Example:
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