How to Populate Array Attributes in Angular Models from API Data

Learn how to set and populate specific array attributes in an Angular model interface with data from REST API in this guide.
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How to Populate Array Attributes in Angular Models from API Data

When working with Angular, you often need to fetch data from APIs to populate your models. A common requirement is to enrich data objects with additional attributes fetched from another resource. In this guide, we’ll delve into a practical scenario where you want to populate the roles attribute of user objects with complete role data from your API.

The Problem

Suppose you have an API endpoint that returns a list of users and another that returns the roles associated with each user. Here’s a basic outline of the data structure you’re dealing with:

Users Endpoint:

Response:

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

User Roles Endpoint:

Response for userId 1:

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

The goal is to create an observable that fetches data from the first endpoint and fills the roles attribute for each user with the additional fields (like roleName) by fetching data from the second endpoint.

Solution Overview

To solve this, we can use the forkJoin operator from RxJS. This operator allows you to listen for multiple observables and gather their results once all of them are complete. Here’s how to implement it in your Angular service:

1. Update Your UserService

Here’s the updated UserService that includes the logic to fetch and populate user roles correctly:

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

2. Explanation of the Code

Step-by-Step Breakdown:

Getting Users: The method getUsers() fetches the users from the API.

Using switchMap: This operator is applied to switch from the user observable to a new observable that handles user roles fetching.

Mapping User Roles Requests: For each user, we create a request using the getUserRoles() method.

Combining Requests with forkJoin: This operator waits for all user role requests to complete and returns an array of results.

Populating Roles: Finally, we map over the users to assign the fetched roles to each user based on their index in the array.

Conclusion

By following this guide, you have learned to effectively populate specific array attributes within an Angular model interface using data fetched from a REST API. This method allows for cleaner and more organized data handling within your application.

Happy coding!