Apa iku Pydantic models ing FastAPI?

Question

Accepted Answer

**Pydantic models** yaiku kelas-kelas (subclass saka `BaseModel`) sing nggawe **struktur, tipe, lan aturan validasi** kanggo data. FastAPI nggunakake dheweke ing kabeh papan — kanggo request bodies, response shapes, lan settings — ndadekake dheweke jantung saka desain type-driven.

## Nggawe model

```python
from pydantic import BaseModel, EmailStr, Field

class User(BaseModel):
    name: str
    email: EmailStr                          # validates email format
    age: int = Field(ge=0, le=120)            # constraint: 0 <= age <= 120
    is_active: bool = True                    # default value
    tags: list[str] = []                      # typed list with a default
```

Saben field ndeklarasi tipe lan batasan/default opsional. Pydantic validasi data marang definisi iki lan ngonversi tipe ing jajahan sing wajar.

## Validasi lan parsing otomatis

```python
@app.post("/users")
def create_user(user: User):                  # FastAPI builds & validates a User from the body
    return user                               # already validated here
# valid JSON → a typed User object; invalid → automatic 422 with field-level errors
```

Kanggone digunakake minangka tipe parameter, FastAPI parse JSON request body menyang model, **validasi** saben field lan bali structured 422 error sing tulad langsang apa sing salah — kabeh otomatis.

## Apa sing Pydantic perangana

```text
✓ Validation — type checks + constraints (lengths, ranges, formats), clear errors
✓ Parsing/coercion — "5" → 5, ISO string → datetime, etc.
✓ Serialization — model.model_dump() / model_dump_json() → dict/JSON
✓ Editor support — full autocomplete & type checking on model attributes
✓ Self-documenting — the model defines the schema used in the auto-generated docs
```

## Siji sumber kabenaran

```text
One Pydantic model drives: request validation, the response schema, the OpenAPI docs,
and typed access in your code → define the data shape ONCE.
```

## Kenapa iku penting

Pydantic models yaiku sudut panggenan FastAPI — dheweke carane sampeyan nggawe lan validasi data sing API sampeyan tampa lan bali, lan meh saben fitur FastAPI maju menyang dheweke.

Karep dheweke penting amarga perangana otomatis **validasi** (kritis kanggo keamanan lan ketegaran — ora manggon marang input mentah), parsing/coercion, serialization, lan editor support, kabeh saka kelas deklaratif siji.

Dheweke ndedhanyang minangka **siji sumber kabenaran**: siji model ndayani request validation, response shape, lan dokumentasi otomatis.

Pendekatan type-driven iki, validate-by-default — nggayuh robust input validation lan error messages sing jernih kurang-luwih gratis — yaiku alasan besar FastAPI mangkono produktif lan aman, ndadekake Pydantic models pengetahuan fundamental, kudu-kudu master.