How to Fix Undefined API Call Parameters on Initial Login in Angular Apps

Discover how to effectively resolve the issue of undefined API call parameters during initial login in Angular applications using .NET and Power BI.
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Resolving Undefined API Call Parameters During Initial Login in Angular Applications

Working with full-stack applications can be challenging, especially when integrating various technologies like Angular, .NET, and Power BI. One common issue developers face is undefined API call parameters during the initial login phase. This post delves into a specific case where a developer encounters this very issue and how to resolve it effectively.

The Problem

In this scenario, a developer is building an Angular application that allows users to save bookmarks for specific Power BI reports. While retrieving user bookmarks through an API

call, they noticed that the parameters required were undefined during the initial login. This results in a failed API call, while subsequent reloads worked without issue. The code snippets provided below outline how the service retrieves user bookmarks and the context in which the API call is made.

API Call Code Snippet

The method for getting user bookmarks is structured as follows:

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

The Component Constructor

The constructor of the component shows how various services are subscribed to, and the order in which they are called:

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

Investigation Steps

After experiencing this issue, the developer attempted several debugging measures to pinpoint the problem:

Checked the order of service calls before API requests were made.

Verified whether the issue resided in the ngOnInit() lifecycle hook.

Utilized RxJS's combineLatest to manage multiple observables.

Despite these efforts, the initial login issue remained unresolved.

The Solution: Switching to BehaviorSubject

Through further investigation, it was discovered that the SelectedReportStore was a regular Subject. Regular subjects don’t emit values until next() is explicitly called, which meant it wasn’t providing the required parameters during the initial API call. The solution was to change the subject to a BehaviorSubject. The BehaviorSubject has a built-in capability to retain the last emitted value, allowing it to emit a value immediately upon subscription.

Why BehaviorSubject?

Immediate Value Emission: As soon as a component subscribes, it will receive the last emitted value.

Retains State: It effectively retains the last state, which is crucial for scenarios like login where values need to be established before an API call.

Code Example

The adjustment to utilize BehaviorSubject in the application would look like this:

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

Conclusion

By switching from a regular Subject to BehaviorSubject, the developer was able to resolve the issue of undefined API parameters during the initial login. Such cases highlight the importance of understanding RxJS and choosing the right type of subject based on the application’s requirements.

If you encounter similar issues in your full-stack applications, consider the flow of your data observables and the implications of using different types of subjects. It can make all the difference in ensuring seamless user experiences.

Feel free to share your experiences or further questions below!