Required query parameters in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a required query parameter in FastAPI?

A required query parameter is a value that the client must provide in the URL query string for the API endpoint to work. FastAPI enforces this by not giving a default value to the parameter.

beginner

How do you declare a required query parameter in FastAPI?

You declare a required query parameter by adding a function argument without a default value in your path operation function. For example: def read_items(q: str): means 'q' is required.

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What happens if a required query parameter is missing in a FastAPI request?

FastAPI automatically returns a 422 Unprocessable Entity error with a message explaining that the required query parameter is missing.

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Can you make a query parameter optional in FastAPI? How?

Yes, by giving the query parameter a default value like None. For example: def read_items(q: str | None = None): makes 'q' optional.

beginner

Why are required query parameters useful in APIs?

They ensure the client provides necessary information for the API to work correctly, preventing errors and making the API behavior predictable.

In FastAPI, how do you make a query parameter required?

A By adding it to the URL path

B By not giving it a default value in the function signature

C By using @required decorator

D By setting it to None

In FastAPI, a query parameter without a default value is required.

What HTTP status code does FastAPI return if a required query parameter is missing?

A 500 Internal Server Error

B 404 Not Found

C 400 Bad Request

D 422 Unprocessable Entity

FastAPI returns 422 Unprocessable Entity when required query parameters are missing.

Which of these makes a query parameter optional in FastAPI?

A q: str = None

B q: str

C q: int

D q: str = ''

Setting a default value like None makes the query parameter optional.

If you want a query parameter 'page' to be required and an integer, how would you declare it?

A def read(page: str):

B def read(page: int = 1):

C def read(page: int):

D def read(page: int | None = None):

Declaring 'page' as int without a default value makes it required.

What is the main benefit of required query parameters?

A They ensure clients send necessary data

B They hide data from clients

C They make the API slower

D They make parameters optional

Required query parameters ensure clients provide needed information for the API to work.

Explain how to declare and use required query parameters in FastAPI.

Think about how function parameters work in Python and how FastAPI uses them.

Describe what happens when a client calls a FastAPI endpoint without providing a required query parameter.

Consider how FastAPI handles validation automatically.