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Learn how to resolve the issue with the Angular `dataSource` filter not functioning after updating it. Follow easy steps to ensure filters work as expected in your Angular MatTable.
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Fixing the Angular dataSource filter Issue After Updating dataSource

When working with Angular applications, particularly when using a MatTable, developers may encounter a frustrating issue where the search filter stops functioning properly after updating the dataSource. This can lead to confusion and wasted time trying to understand the root cause of the problem. In this guide, we will explore the issue in detail and provide a clear, step-by-step solution to ensure your filtering works as intended.

The Problem: Search Filter Malfunctioning

In a typical setup with Angular's MatTable, you might implement a search feature like below:

[[See Video to Reveal this Text or Code Snippet]]

This function is designed to update the filter of the dataSource based on user input. However, after updating the dataSource in a separate function, the filtering appears to stop working. The main symptoms include:

Searching yields no results unless the filter is empty.

A previously entered filter value might still allow all data to be displayed if re-entered.

This unexpected behavior can severely impact the usability of your application.

The Solution: Maintain a Consistent dataSource Instance

The root of the issue lies in the way the dataSource is updated. Each time a new instance of TableVirtualScrollDataSource is created, it becomes disconnected from the existing filter settings. Instead of creating a new instance upon every data update, you should modify the existing instance. Here’s how you can achieve this.

Steps to Fix the Filtering Issue

Initialize the Data Source Once: Only create a new instance of TableVirtualScrollDataSource during the initialization phase.

Update Data Without Re-instantiating: Modify the existing data within the initialized dataSource instance.

Here’s how to implement these steps in code:

Step 1: Initialize the dataSource

Instead of redefining the dataSource in your initData() method, simply update its data property:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Update Your OnChange Method

When the onChange() function is called to modify the data, use the data property to reflect the changes:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of Changes

By keeping the same instance of dataSource, the filter retains its configuration and functionality.

Modifying the data property allows you to manage the data more dynamically, preserving the relationship with the filter.

Conclusion

By following the steps outlined above, you can resolve issues surrounding the dataSource filter in your Angular MatTable. The key takeaway is to maintain a consistent dataSource instance throughout your application's lifecycle—updating its properties rather than creating new instances will ensure your filters function as expected. If you encounter similar issues in the future, remember this approach as a reliable solution.

Now your Angular table filters will be working smoothly, enhancing the user experience of your application!