FastAPI Tutorial – Path Validations

Today, we will be discussing how to use path validations in FastAPI. Path validations are a powerful feature that allows you to validate the incoming path parameters in your API routes. This ensures that the data being passed to your application is valid and meets certain criteria before processing it.

Using Path Validations in FastAPI

To use path validations in FastAPI, you can create a route with a parameter that is annotated with a type hint and then add additional validation criteria using the `…` syntax. For example:

from fastapi import FastAPI

app = FastAPI()

@app.get("/items/{item_id}")
async def get_item(item_id: int):
    return {"item_id": item_id}

In the above example, the route `/items/{item_id}` expects an integer value for the `item_id` parameter. If a non-integer value is passed, FastAPI will automatically return a `422 Unprocessable Entity` response with a detailed error message.

You can also add additional validation criteria to the parameter by using the `…` syntax. For example, to ensure that the `item_id` parameter is greater than zero, you can write:

@app.get("/items/{item_id}")
async def get_item(item_id: int, item_name: str = Query(..., min_length=1)):
    return {"item_id": item_id, "item_name": item_name}

In this example, we are using the `Query` class to add additional validation criteria to the `item_name` parameter. By setting `min_length=1`, we are ensuring that the value of `item_name` must be at least 1 character long. If the validation criteria is not met, FastAPI will automatically return a `422 Unprocessable Entity` response.

Conclusion

Path validations are a powerful feature in FastAPI that allows you to easily validate the incoming path parameters in your API routes. By adding additional validation criteria to your route parameters, you can ensure that the data being passed to your application is valid and meets certain criteria before processing it.

Thank you for reading this tutorial on path validations in FastAPI. We hope you found it helpful and informative. Happy coding!