How to Successfully Handle File Uploads in ASP.NET Core Controllers

Troubleshooting file uploads in ASP.NET Core? Learn how to correctly send files from your form to the controller without the files being empty.
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How to Successfully Handle File Uploads in ASP.NET Core Controllers

When working with file uploads in ASP.NET Core, one common issue that developers face is sending files from a front-end form to a controller action, only to find that the files collection is empty on the server-side. This can be frustrating and can derail your project timeline. In this guide, we will explore how to troubleshoot this problem and ensure that your file uploads work as intended.

The Problem: Files Are Always Empty

In a recent scenario, a user attempted to implement file uploads using a modal form, but found that the list of files being received in the controller was consistently empty. The initial struggle stemmed from how the file input was set up and the handling of the file upload request. Understanding how to properly configure the file input and the AJAX call to the ASP.NET Core controller is vital for successful uploads.

Code Overview

Here’s a quick look at the initial setup provided for handling file uploads in the code:

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The Solution: Correctly Configuring File Uploads

To ensure files are correctly sent and received, you need to make several adjustments in your HTML and JavaScript code.

Step 1: Modify the File Input Element

To allow multiple file uploads, include the multiple attribute in the file input:

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Step 2: Update Your JavaScript Function

When submitting the form, it’s important to prevent the default form submission. Also, you need to correctly construct the FormData object to include multiple files. Here’s how to do that with the updated JavaScript function:

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Step 3: Update the Controller Action

Ensure your controller action method is properly configured to receive multiple files through a List<IFormFile> parameter:

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Summary

By making these adjustments, you ensure that your file uploads from the front-end form are successfully sent to the ASP.NET Core controller without the files being empty. Key points include:

Use the multiple attribute on your file input when expecting multiple file uploads.

Construct FormData appropriately in your JavaScript.

Ensure your controller can handle a list of files.

With these steps, you can troubleshoot and resolve issues related to file uploads in your ASP.NET Core application effectively. Happy coding!