Fast API Invalid Query Parameter Type
Understanding FastAPI
FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.7+ based on standard Python type hints. It is designed to be easy to use and to provide high performance, on par with NodeJS and Go. FastAPI is particularly useful for building RESTful APIs quickly and efficiently.
Identifying the Symptom: Invalid Query Parameter Type
When working with FastAPI, you might encounter an error related to query parameters. A common symptom of this issue is receiving an error message indicating that the query parameter type does not match the expected type. This can lead to unexpected behavior or application crashes.
Example Error Message
When this issue occurs, you might see an error message similar to the following:
422 Unprocessable Entity: {'detail': [{'loc': ['query', 'param_name'], 'msg': 'value is not a valid integer', 'type': 'type_error.integer'}]}
Details About the Issue
The error arises when the type of a query parameter provided in a request does not match the type expected by the FastAPI application. FastAPI uses Python type hints to validate request data, and if the data does not conform to the expected type, it raises a validation error.
Common Causes
- Providing a string where an integer is expected.
- Using a float when an integer is required.
- Incorrectly formatted data types.
Steps to Fix the Issue
To resolve the 'Invalid Query Parameter Type' error, follow these steps:
Step 1: Verify the Expected Type
Check the FastAPI endpoint definition to determine the expected type for the query parameter. For example:
from fastapi import FastAPI, Query
app = FastAPI()
@app.get("/items/")
async def read_items(q: int = Query(...)):
return {"q": q}
In this example, the query parameter q is expected to be an integer.
Step 2: Ensure Correct Parameter Type in Requests
When making requests to the FastAPI application, ensure that the query parameters match the expected types. For instance, if the parameter is expected to be an integer, do not provide a string or float.
import requests
response = requests.get("http://localhost:8000/items/?q=10")
print(response.json())
Step 3: Use Type Conversion if Necessary
If the input data is not in the correct type, consider converting it before sending the request. For example, convert a string to an integer if required.
Additional Resources
By following these steps, you can resolve the 'Invalid Query Parameter Type' error and ensure that your FastAPI application handles requests as expected.
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