Query parameter validation in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is query parameter validation in FastAPI?

It is the process of checking and enforcing rules on the data sent as query parameters in a URL to ensure they meet expected types and constraints before processing.

beginner

How do you declare a required query parameter in FastAPI?

By defining a function parameter without a default value or using Query(...) to explicitly mark it as required.

intermediate

What does the Query() function do in FastAPI?

It allows you to declare metadata and validation rules for query parameters, like default values, minimum or maximum length, and descriptions.

intermediate

How can you enforce a minimum and maximum value for a numeric query parameter in FastAPI?

Use Query() with parameters like ge (greater than or equal) and le (less than or equal) to set minimum and maximum limits.

beginner

What happens if a query parameter fails validation in FastAPI?

FastAPI automatically returns a clear error response with status code 422 and details about the validation failure.

Which FastAPI function is used to add validation rules to query parameters?

A Body()

B Path()

C Query()

D Header()

Query() is used to declare and validate query parameters in FastAPI.

How do you make a query parameter optional with a default value of 10?

A param: int

B param: int = Query(10)

C param: int = 10

D param: int = Query()

Using Query(10) sets the default value to 10 and makes the parameter optional.

What validation keyword enforces a minimum length for a string query parameter?

A min_length

B min_value

C length_min

D minsize

min_length is the correct keyword to set minimum string length in Query().

If a query parameter is missing but required, what status code does FastAPI return?

A 500

B 404

C 400

D 422

FastAPI returns 422 Unprocessable Entity for validation errors including missing required parameters.

Which of these is NOT a valid way to declare a query parameter in FastAPI?

A param: int = Body(...)

B param: int = 5

C param: int

D param: int = Query(..., ge=1, le=10)

Body() is used for request body parameters, not query parameters.

Explain how to validate a query parameter that must be an integer between 1 and 100 in FastAPI.

Think about using Query() with minimum and maximum value constraints.

Describe what happens when a client sends a query parameter that does not meet the validation rules in FastAPI.

Consider how FastAPI handles invalid input automatically.