Example data in schema in FastAPI - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this FastAPI schema example?

Given this Pydantic model with example data, what will the OpenAPI schema show for the example?

FastAPI

from pydantic import BaseModel, Field

class User(BaseModel):
    id: int = Field(..., example=123)
    name: str = Field(..., example="Alice")

user_example = User.schema()['properties']

A {"id": {"title": "Id", "type": "integer", "example": 123}, "name": {"title": "Name", "type": "string", "example": "Alice"}}

B {"id": {"title": "Id", "type": "string", "example": "123"}, "name": {"title": "Name", "type": "string", "example": "Alice"}}

C {"id": {"title": "Id", "type": "integer"}, "name": {"title": "Name", "type": "string"}}

D {"id": {"title": "Id", "type": "integer", "example": "Alice"}, "name": {"title": "Name", "type": "string", "example": 123}}

💡 Hint

Look at the Field example values and their types.

The example values in the schema match the Field example arguments with correct types.

📝 Syntax

intermediate

Which option correctly sets example data in a Pydantic schema?

Choose the code snippet that correctly uses Field to add example data for a Pydantic model.

A

class Item(BaseModel):
    price: float = Field(..., example=19.99)

B

class Item(BaseModel):
    price: float = Field(example=19.99)

C

class Item(BaseModel):
    price: float = Field(..., example='19.99')

D

class Item(BaseModel):
    price: float = Field(..., example=price)

💡 Hint

Example should match the field type and use ... for required fields.

Option A correctly uses Field with required marker ... and example as a float matching the type.

🔧 Debug

advanced

What error occurs with this example data in schema?

This Pydantic model has example data that does not match the field type. What error will FastAPI raise when generating docs?

FastAPI

from pydantic import BaseModel, Field

class Product(BaseModel):
    quantity: int = Field(..., example="ten")

A No error, example is accepted as string

B SyntaxError: invalid syntax in Field example

C ValidationError: example value is not valid for type int

D TypeError: example must be int, got str

💡 Hint

Example must match the declared field type.

Pydantic validates example values against the field type and raises ValidationError if mismatched.

❓ state_output

advanced

What is the example output in OpenAPI for nested Pydantic models?

Given nested models with example data, what does the OpenAPI example show for the nested field?

FastAPI

from pydantic import BaseModel, Field

class Address(BaseModel):
    city: str = Field(..., example="Paris")

class User(BaseModel):
    name: str = Field(..., example="Bob")
    address: Address = Field(...)

user_schema = User.schema()

A {"name": {"example": "Bob"}, "address": {}}

B {"name": {"example": "Bob"}, "address": {"$ref": "#/definitions/Address"}}

C {"name": {"example": "Bob"}, "address": {"example": "Paris"}}

D {"name": {"example": "Bob"}, "address": {"example": {"city": "Paris"}}}

💡 Hint

Nested models use $ref in schema, examples are inside referenced model.

The User schema references Address by $ref; example for nested fields is inside Address schema.

🧠 Conceptual

expert

How does FastAPI use example data in schema for API docs?

Why is setting example data in Pydantic models important for FastAPI-generated OpenAPI docs?

A It enforces runtime validation of incoming data to match the example values exactly.

B It automatically generates database seed data from the examples.

C It disables schema validation and trusts example data as the only valid input.

D It provides sample request and response data shown in the API docs to help users understand the API.

💡 Hint

Think about the purpose of examples in documentation.

Examples improve API docs by showing sample data, making it easier for users to test and understand endpoints.