How to Add Both File and JSON Form in a FastAPI POST Request

Learn how to effectively combine file uploads and JSON data in a FastAPI POST request, ensuring seamless interaction with your APIs.
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How to Add Both File and JSON Form in a FastAPI POST Request

FastAPI is a powerful web framework for building APIs in Python, but when combining file uploads with JSON data in a POST request, developers may encounter challenges. One common issue is the 400 Bad Request error, which indicates that the server could not understand the request due to malformed syntax. In this guide, we will explore how to properly structure a POST request in FastAPI that includes both file uploads and JSON data while avoiding common pitfalls.

Problem Overview

You have set up a FastAPI application and are trying to send a POST request that includes both an uploaded image file and some metadata (in this example, the farm_name). However, you are experiencing a 400 Bad Request error. Here's a simplified outline of what your setup looks like:

FastAPI Application (app.py)

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

Python Code for Sending a Request (test.py)

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

Solution

1. Understanding Content Types

One critical aspect of sending multipart form data is the handling of the Content-Type. The requests library in Python automatically manages this header, including the necessary boundary definitions. Therefore, if you set this header manually, you can inadvertently disrupt the request format.

2. Correcting the Request Headers

To avoid the error, modify your request by removing the Content-Type header from the headers dictionary in test.py. Your updated header section should look like this:

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

This change allows the requests library to handle the multipart/form-data encoding properly, ensuring that the FastAPI server receives the request formatted correctly.

3. Final Example Code for Sending a Request

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

4. Testing the Implementation

Before sending the request, ensure that your FastAPI application is running. Start it with the command:

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

Then execute the test.py file to send the POST request. You should no longer see the 400 Bad Request error, and the server should return the expected response containing the farm_name.

Conclusion

By correctly managing the Content-Type header and structuring your POST request appropriately, you can successfully send both file and JSON form data using FastAPI. This allows for more complex API interactions and can significantly enhance the capabilities of your applications.

Feel free to explore additional functionalities of FastAPI, such as extracting more metadata from the uploaded files or validating the input data. Happy coding!