How to Post JSON Data from JavaScript to FastAPI and Avoid a 422 Unprocessable Entity Error?

Posting JSON Data from JavaScript to FastAPI

In this scenario, the goal is to pass a value called 'ethAddress' from an input form on the client to FastAPI for use in chart generation. However, a 422 Unprocessable Entity error occurs. Analysis of the issue reveals that the problem lies in the way FastAPI interprets 'ethAddress' as a query parameter, expecting it to be part of the URL.

To resolve this issue, you have several options depending on your specific requirements:

Option 1: Create a Pydantic Model

Define a Pydantic model to handle the data structure you expect to receive from the client. In this case, create an Item class with a single 'eth_addr' field.

Option 2: Use the Body Type

Alternatively, use the FastAPI Body type to denote that the parameter is to be interpreted from the body of the request.

Option 3: Embed the Body Parameter

If you have a single body parameter, you can simplify the code further by using the embed=True argument in the Body type, which allows FastAPI to parse the JSON data directly from the embedded body.

Sending JSON Data from JavaScript

Once you have adjusted the backend, you can configure the JavaScript client to send the JSON data accordingly. Ensure that you set the appropriate headers (e.g., 'Content-Type': 'application/json') and use JSON.stringify to prepare the data before sending it through fetch.

Additional Resources

For more detailed guidance and JavaScript examples on posting JSON data, refer to the following resources:

• https://fastapi.tiangolo.com/tutorial/body/
• https://stackoverflow.com/questions/64357060
• https://stackoverflow.com/questions/64762081
• https://stackoverflow.com/questions/64266617

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