Скачать или смотреть How to Implement an Asynchronous API Method for File Uploads in Your Angular App

Discover how to make your web API calls asynchronous so that users can navigate your Angular app while waiting for file upload results.
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This video is based on the question https://stackoverflow.com/q/69131999/ asked by the user '5ra' ( https://stackoverflow.com/u/11546833/ ) and on the answer https://stackoverflow.com/a/69132462/ provided by the user 'OlegI' ( https://stackoverflow.com/u/7085070/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

When building a web application that involves file uploads, it is common to encounter situations where your users must wait for the file to be processed, especially if the process takes a significant amount of time (1-2 minutes in this case). This wait time can lead to frustration, as users are often left staring at a loading screen.

In this guide, we will explore how to transform a synchronous API method into an asynchronous one, allowing your users to continue navigating your application while their files are processed. We will breakdown several solutions to achieve this functionality, ensuring a better user experience.

Understanding the Problem

The original API method, as provided, is synchronous:

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In its current state, this method requires users to wait for the entire file-checking process to complete before receiving any feedback about their upload status. The goal is to enable users to remain active within the application during this process.

Solutions Overview

To change the synchronous behavior of your API and allow for background processing, you can either:

Polling: Regularly check the server to see if the process is complete.

WebSockets: Establish a two-way communication channel that lets the server notify the client when processing is done.

Let’s dive deeper into both options.

1. Polling

What is Polling?

Polling involves sending periodic requests from the client (i.e., your Angular app) to the server asking if the upload processing is complete. Here's a step-by-step breakdown of how to implement it:

Step 1: Update your API to return a unique identifier for the file upload when the files are received.

Step 2: Implement an endpoint on your API that checks the status of the file validation using this identifier.

Step 3: In your Angular app, set up an interval to make requests to the status-checking endpoint every few seconds.

Pros and Cons

Pros:

Simple to implement.

Cons:

Can be inefficient due to periodic requests.

May involve unnecessary server load.

2. WebSockets

What are WebSockets?

WebSockets provide a more efficient way to handle this by creating a persistent, two-way communication channel between the client and server. The server can push messages to the client, informing it when the processing is complete.

Step 1: Implement a WebSocket server.

Step 2: Connect your Angular client to this WebSocket.

Step 3: Emit a message from the server once the file processing is done, notifying the client.

Pros and Cons

Pros:

Real-time updates.

Lower server load as no repetitive polling is required.

Cons:

More complex to implement and may require using libraries like ASP.NET SignalR.

Conclusion

Both polling and WebSockets serve as effective solutions for handling long-running processes like file uploads. While polling is simpler and straightforward, WebSockets offer a more efficient and user-friendly approach. Depending on your skill level and project requirements, you can choose the method that works best for you.

By implementing these changes, your users will no longer feel stuck waiting for their uploads to complete; instead, they can smoothly navigate your Angular application while receiving timely updates about their file status.

Incorporating asynchronous API methods enhances user experience and can significantly improve satisfaction with your application.