FastAPI: Validate Parameters with Query and Path
FastAPI's `Query` and `Path` objects let you declare rich validation rules directly in your function's signature. Enforce string lengths, regex patterns, or numeric ranges on URL parameters without writing manual checks.
Go beyond basic type hints in FastAPI by using `Query` and `Path` for declarative validation. Instead of just `item_id: int`, you can specify `item_id: Annotated[int, Path(gt=0)]` to ensure the ID is a positive integer. This applies to query parameters too, letting you set min/max length or regex patterns for search strings. The common footgun is writing manual `if/else` validation logic inside your endpoint, which FastAPI can handle for you, returning a clean 422 error on failure.
Read the original → fastapi.tiangolo.com
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