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A guide on selecting multiple defaults in Angular Material's mat-select using complex objects with FormControl.
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How to Select All Options in Angular Material's mat-select with FormControl

When working with Angular Material's mat-select, you might encounter a scenario where you want to pre-select multiple options, especially when dealing with complex objects. In this post, we’ll tackle a common problem: how to select all the options, including a special "All" option, by default in a mat-select component.

Understanding the Problem

Suppose you have a dropdown that displays various cars, and you wish to allow users to either select individual cars or opt to select all vehicles at once. Here’s a challenge you might face:

You want to set default values in a FormControl for a mat-select that comprises complex objects—and possibly a special "All" option.

Default selection isn't working as expected, and debugging this can be confusing.

In our case, we have a Car model and a form group which should bind to the selection of car options, including the "All" option.

Setting Up the FormGroup

Initially, you need to structure your form correctly and define the data model. Below is an example of a Car type and how you can set up the FormGroup.

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

Creating the All Option

You should be able to create a separate Car object for the "All" option:

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

This helps to manage the selection of the "All" option effectively. This step is crucial—rather than trying to instantiate it on the fly, having a dedicated object allows you to reference it easily.

Updating the HTML

Next, update your HTML to bind these values properly in the mat-select component:

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

Key Changes Explained

Setting the value: Ensure that you bind the entire Car object to the value attribute for each mat-option, including the "All" option. This allows Angular to manage the selection correctly.

Using multiple: The multiple attribute allows users to select multiple options, which is essential for our use case.

Conclusion

With the steps above, you can configure your Angular Material mat-select to select multiple default options, including an "All" option, using complex objects.

This method adheres to best practices while maintaining readability and functionality in your forms. By creating a dedicated Car object for the "All" option and ensuring the values are correctly managed in FormControls, you can easily enhance user experience on your application.

Now you’ve got a reliable approach to tackle this issue in your Angular Material project!