Example data in schema in FastAPI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of example data in a FastAPI schema?

Example data helps show what kind of input or output the API expects or returns. It makes the API easier to understand and test.

beginner

How do you add example data to a Pydantic model in FastAPI?

You add example data by using the <code>Config</code> class inside the model and setting <code>schema_extra</code> with an <code>example</code> dictionary.

beginner

Show a simple example of a Pydantic model with example data.

class Item(BaseModel):<br>  &nbsp;&nbsp;name: str<br>  &nbsp;&nbsp;price: float<br>  &nbsp;&nbsp;class Config:<br>  &nbsp;&nbsp;&nbsp;&nbsp;schema_extra = {<br>  &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"example": {"name": "Apple", "price": 1.2}<br>  &nbsp;&nbsp;&nbsp;&nbsp;}<br>This example shows an item with a name and price.

beginner

Why is example data useful in FastAPI's automatic docs?

Example data appears in the docs so users can see sample inputs and outputs. This helps them understand how to use the API without guessing.

intermediate

Can you add multiple examples in FastAPI schemas?

Yes, you can add multiple examples by using examples instead of example in schema_extra. Each example has a name and value.

How do you add example data to a Pydantic model in FastAPI?

A By adding a method called example()

B Using the Config class with schema_extra and example

C Using a decorator @example_data

D By setting an attribute called example_data

Example data is added inside the Config class using schema_extra with an example dictionary.

What is the benefit of example data in FastAPI docs?

A It makes the docs colorful

B It hides sensitive data

C It shows sample inputs and outputs to help users understand the API

D It speeds up the API response

Example data helps users by showing sample inputs and outputs in the docs.

Which keyword is used inside schema_extra to provide a single example?

A example

B sample

C examples

D demo

The keyword 'example' is used for a single example inside schema_extra.

How can you provide multiple examples in FastAPI schema?

A Use multiple schema_extra blocks

B Use a separate file for examples

C Add a list to the example keyword

D Use the examples keyword inside schema_extra with named examples

Multiple examples are provided using the 'examples' keyword with named example objects.

Where does FastAPI show the example data you add to schemas?

A In the automatic interactive API docs (Swagger UI and ReDoc)

B In the API response only

C In the server logs

D In the database

FastAPI shows example data in the automatic API docs like Swagger UI and ReDoc.

Explain how to add example data to a Pydantic model in FastAPI and why it is helpful.

Think about the Config class and schema_extra attribute.

Describe how you can provide multiple example inputs in a FastAPI schema and where these examples appear.

Use 'examples' instead of 'example' for multiple samples.

Practice

1. What is the main purpose of adding example data in a FastAPI schema field?

easy

A. To automatically generate database tables

B. To validate the data type of the field at runtime

C. To encrypt the field data before sending

D. To show sample values for API fields to help users understand expected data

Solution

1. Step 1: Understand the role of example data in FastAPI

   Example data is used to provide sample values in API documentation, helping users know what to send or expect.

2. Step 2: Differentiate example data from validation or encryption

   Example data does not validate or encrypt; it only shows sample values in docs.

3. Final Answer:

   To show sample values for API fields to help users understand expected data -> Option D

4. Quick Check:

   Example data = sample values [OK]

Hint: Example data shows sample values in docs, not validation [OK]

Common Mistakes:

• Confusing example with validation
• Thinking example encrypts data
• Assuming example creates database schema

2. Which of the following is the correct way to add example data to a Pydantic model field in FastAPI?

easy

A. name: str = Field(example="John Doe")

B. name: str = Field(default="John Doe")

C. name: str = Field(description="John Doe")

D. name: str = Field(required=True)

Solution

1. Step 1: Recall the Field syntax for example data

   FastAPI uses Field(..., example=...) to add example data to schema fields.

2. Step 2: Identify the correct option

   name: str = Field(example="John Doe") uses Field(example="John Doe"), which is the correct syntax for example data.

3. Final Answer:

   name: str = Field(example="John Doe") -> Option A

4. Quick Check:

   Field(example=...) = correct syntax [OK]

Hint: Use Field(example=...) to add example data [OK]

Common Mistakes:

• Using default instead of example
• Confusing description with example
• Omitting Field() entirely

3. Given this Pydantic model in FastAPI:

from pydantic import BaseModel, Field

class User(BaseModel):
    username: str = Field(..., example="alice123")
    age: int = Field(..., example=30)

What example data will appear in the OpenAPI docs for the age field?

medium

A. "30"

B. 30

C. None

D. 0

Solution

1. Step 1: Check the example value assigned to the age field

   The age field has example=30, which is an integer value 30.

2. Step 2: Understand how example data is shown in docs

   FastAPI shows the example exactly as given, so the example for age will be 30 (integer).

3. Final Answer:

   30 -> Option B

4. Quick Check:

   Example for age = 30 [OK]

Hint: Example shows exact value given in Field(example=...) [OK]

Common Mistakes:

• Thinking example converts int to string
• Assuming example is None if not set
• Confusing example with default value

4. Identify the error in this FastAPI Pydantic model using example data:

from pydantic import BaseModel, Field

class Item(BaseModel):
    name: str = Field(example=123)
    price: float = Field(..., example="9.99")

medium

A. Example for name should be a string, not an integer

B. Missing default value for name field

C. Example for price should be a float, not a string

D. Field(...) is missing for name field

Solution

1. Step 1: Check example data types against field types

   The name field is str but example=123 (int) is allowed but not ideal; price is float but example="9.99" is a string, which is incorrect.

2. Step 2: Identify the type mismatch causing error

   Example for price should be a float (9.99), not a string "9.99"; this can cause schema confusion.

3. Final Answer:

   Example for price should be a float, not a string -> Option C

4. Quick Check:

   Example type must match field type [OK]

Hint: Match example type to field type exactly [OK]

Common Mistakes:

• Using string example for numeric fields
• Ignoring type mismatch warnings
• Omitting Field(...) for required fields

5. You want to create a FastAPI schema for a product with a nested model and provide example data for both levels. Which is the correct way to add example data for nested fields?

hard

A. Use example in Field() for each nested field separately

B. Add example data only to the top-level model, nested fields inherit automatically

C. Use example only in the nested model class, not in the parent

D. Example data cannot be added to nested models in FastAPI

Solution

1. Step 1: Understand example data usage in nested models

   Each field in nested models needs its own example data using Field(example=...) to show correct samples in docs.

2. Step 2: Confirm nested fields do not inherit example data

   Example data is not inherited; you must specify it explicitly for each nested field.

3. Final Answer:

   Use example in Field() for each nested field separately -> Option A

4. Quick Check:

   Example data must be set per field [OK]

Hint: Add example=... to every nested field explicitly [OK]

Common Mistakes:

• Assuming nested fields inherit example data
• Skipping example in nested models
• Thinking example data is only for top-level fields