Pydantic validation trong FastAPI hoạt động thế nào?

from pydantic import BaseModel, EmailStr, Field, field_validator

class UserCreate(BaseModel):
    name: str = Field(min_length=2, max_length=50)
    email: EmailStr
    age: int = Field(ge=0, le=150)

    @field_validator('name')
    @classmethod
    def name_alpha(cls, v: str) -> str:
        if not v.replace(' ', '').isalpha():
            raise ValueError('Only letters allowed')
        return v.strip().title()

    model_config = {"from_attributes": True}  # Pydantic v2

@app.post("/users", status_code=201)
async def create_user(user: UserCreate):  # Auto-validated!
    ...