FastAPI Request Models

Introduction

Define data models with Pydantic for request/response validation.

Pydantic Models

from pydantic import BaseModel, Field, EmailStr

class UserBase(BaseModel):
    email: EmailStr
    username: str = Field(..., min_length=3, max_length=50)

class UserCreate(UserBase):
    password: str = Field(..., min_length=8)

class User(UserBase):
    id: int
    is_active: bool = True
    
    class Config:
        from_attributes = True

class UserUpdate(BaseModel):
    email: EmailStr | None = None
    password: str | None = None

Nested Models

class Address(BaseModel):
    street: str
    city: str
    country: str

class UserWithAddress(UserBase):
    addresses: list[Address] = []

class Order(BaseModel):
    items: list[Item]
    total: float

File Uploads

from fastapi import File, UploadFile

@app.post("/upload")
async def upload_file(file: UploadFile = File(...)):
    contents = await file.read()
    return {"filename": file.filename, "size": len(contents)}

Practice Problems

1. Create nested Pydantic models
2. Add field validation
3. Handle file uploads
4. Use optional fields
5. Convert between models