Example data in schema in FastAPI - Step-by-Step Execution

Concept Flow - Example data in schema

Define Pydantic Schema

↓

Add example data in Config

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Use schema in FastAPI endpoint

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Auto-generate docs show example

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Client sees example data in docs

This flow shows how to add example data to a Pydantic schema and how FastAPI uses it to show examples in API docs.

Execution Sample

FastAPI

from pydantic import BaseModel

class User(BaseModel):
    name: str
    age: int

    class Config:
        schema_extra = {"example": {"name": "Alice", "age": 30}}

Defines a User schema with example data that FastAPI will show in API docs.

Execution Table

Step	Action	Evaluation	Result
1	Define User schema with fields name and age	Class created	User schema ready
2	Add example data in Config.schema_extra	Example attached	{"name": "Alice", "age": 30} available
3	Use User schema in FastAPI endpoint	Endpoint accepts User	Example shown in docs
4	Client opens docs	Docs render example	Example data visible to client
5	Client sends request with example data	Request accepted	Server processes User data
6	End of flow	No more steps	Execution stops

💡 All steps completed, example data is used in docs and requests

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
User.schema_extra	None	{"example": {"name": "Alice", "age": 30}}	{"example": {"name": "Alice", "age": 30}}	{"example": {"name": "Alice", "age": 30}}
FastAPI endpoint	Not defined	Not defined	Uses User schema	Uses User schema with example

Key Moments - 2 Insights

Why does the example data appear in the API docs?

Because the example is set inside the schema's Config.schema_extra, FastAPI reads it and shows it automatically in the docs (see execution_table step 4).

Does the example data affect the actual data validation?

No, example data is only for documentation and testing help. Validation uses the schema fields, not the example (see execution_table step 5).

Visual Quiz - 3 Questions

Look at the execution table, at which step is the example data attached to the schema?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Check the 'Action' column for when example data is added to Config.schema_extra.

According to the variable tracker, what is the value of User.schema_extra after step 3?

A {"example": {"name": "Alice", "age": 30}}

B None

C Empty dictionary

D Undefined

💡 Hint

Look at the 'After Step 3' column for User.schema_extra in variable_tracker.

If we remove the example from Config, what will happen in the docs?

A Docs will break and not load

B Docs will show no example data

C Docs will show the last example data anyway

D Docs will show an error message

💡 Hint

Refer to the concept_flow where example data is added to show in docs.

Concept Snapshot

Define a Pydantic schema with fields
Add example data inside Config.schema_extra
Use schema in FastAPI endpoint
FastAPI auto-shows example in docs
Example helps users understand API input
Example does not affect validation

Full Transcript

This visual execution shows how to add example data to a Pydantic schema in FastAPI. First, you define a schema class with fields like name and age. Then, inside the Config class, you add schema_extra with an example dictionary. When you use this schema in a FastAPI endpoint, the example data automatically appears in the generated API documentation. This helps clients see sample input data. The example data is only for docs and does not affect how FastAPI validates incoming requests. The execution table traces each step from defining the schema to the client seeing the example in docs. The variable tracker shows how the example data is stored in the schema. Key moments clarify common confusions about example usage and validation. The quiz tests understanding of when and how example data is attached and used.