Pundi apa cara mengelola settings nganggo Pydantic?

Question

Accepted Answer

FastAPI applications mengelola configuration nganggo **`pydantic-settings`** (`BaseSettings`) — kelas sing maca config saka **environment variables** (lan `.env` files) nganggo **validation lan type conversion**, nyegah secrets dijupuk ing code lan njamin config bener ing startup.

## Nggolongake settings

```python
from pydantic_settings import BaseSettings

class Settings(BaseSettings):
    app_name: str = "My API"
    database_url: str                       # required — must be provided
    secret_key: str                          # required (a secret)
    debug: bool = False
    max_connections: int = 10

class Config:
        env_file = ".env"                    # also read from a .env file

settings = Settings()                        # reads & VALIDATES env vars at startup
```

`BaseSettings` sacara otomatis maca saben field saka matching **environment variable** (contone `DATABASE_URL`), ngubah types (`"true"` → `bool`, `"10"` → `int`), lan **validate** — nilai required sing ilang utawa type sing salah bakal gagal langsung ing startup nganggo error sing jelas (fail-fast).

## Nggunakake settings (via dependency injection)

```python
from functools import lru_cache
from fastapi import Depends

@lru_cache                              # create the Settings once (cached)
def get_settings():
    return Settings()

@app.get("/info")
def info(settings: Settings = Depends(get_settings)):
    return {"app": settings.app_name, "debug": settings.debug}
```

Nyuntik settings via cached dependency gawe dheweke **testable** (override ing tests) lan njamin siji instance.

## File .env lan secrets

```bash
# .env — local config, GITIGNORED (never commit secrets)
DATABASE_URL=postgresql://localhost/mydb
SECRET_KEY=dev-secret
DEBUG=true
```

```text
✓ Keep secrets in env vars / .env (gitignored); commit a .env.example documenting keys
✓ In production, inject config via the platform's environment / secret manager
✓ Validation at startup catches misconfiguration immediately (not deep in a request)
```

## Mengapa iki penting

Settings management sing bener yaiku **operational necessity** (apps butuh config beda ing dev/staging/production) lan **security requirement** (secrets kaya database URLs lan keys ora boleh hardcoded ing source control — breach sing umum lan serius).

Pydantic `BaseSettings` menehi solusi idiomatic FastAPI, lan mangerteni iku penting kanggo ngelmuning saben dina.

Advantage utama: maca config saka **environment variables** (nyegah secrets saka code, twelve-factor approach) nganggo **type conversion lan validation** otomatis — dadi misconfiguration gagal cepet ing startup nganggo error sing jelas tinimbang failure runtime sing nggegirisi.

Digabung nganggo dependency injection (gawe settings testable lan singleton) lan cara gitignored `.env` files kanggo development lokal, iki menehi configuration aman, validate, lan sesuai lingkungan.

Nangerteni cara nggolongake settings, nggunakake dheweke via DI, lan handle secrets kanthi aman yaiku fundamental kanggo bangun FastAPI applications sing production-ready.