POST /items: Adding New Data to Your API with FastAPI & Pydantic

From Read-Only to Interactive Until now our API could only read data. Today we add the ability to CREATE : the C in CRUD. The Request & Response DTOs Request : what the client sends class ItemCreateDTO(BaseModel): name: str description: Optional[str] = None price: float @field_validator("price") def price_must_be_positive(cls, v): if v <= 0: raise ValueError("Price must be a positive number") return v Response : what the API returns class ItemResponseDTO(BaseModel): id: int name: str description: Optional[str] price: float created_at: datetime Two separate DTOs : one for input, one for output. That's clean API design. The POST Endpoint @app.post("/items", response_model=ItemResponseDTO, status_code=201) def create_item(item: ItemCreateDTO): db = SessionLocal() new_item = Item( name=item.name, description=item.description, price=item.price ) db.add(new_item) db.commit() db.refresh(new_item) db.close() return new_item Notice status_code=201 : that's the correct HTTP status for a successf