Ni nini miundo ya Pydantic katika FastAPI?

Question

Accepted Answer

**Miundo ya Pydantic** ni madarasa (inayoithi `BaseModel`) ambayo inafafanua **muundo, aina, na kanuni za uhalali** wa data. FastAPI inatumia zote kila mahali — kwa miili ya ombi, maumbo ya majibu, na mipangilio — ikiwa ni jantiri la muundo unaounganishwa na aina.

## Kufafanua muundo

```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
```

Kila shamba linabainisha aina na mapungufu/chaguomsingi ya ikhtiari. Pydantic huhalali data dhidi ya ufafanuzi huu na hubadilisha aina mahali ambapo zinaeleweka.

## Uhalali otomatiki na uchambuzi

```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
```

Kinatumika kama aina ya parameter, FastAPI inapokea mwili wa ombi la JSON kwenye muundo, **huhalali** kila shamba na inarudisha kosa la muundo 422 linaloandika kwa nguvu ni nini kina kasoro — kila kitu kiotomatiki.

## Kile Pydantic kinakupa

```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
```

## Chanzo kimoja cha ukweli

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

## Kwa nini ni muhimu

Minundo ya Pydantic ni kisimu cha msingi cha FastAPI — ni jinsi unayofafanua na kuhalali data ambayo API yako inakubali na kurudisha, na karibu kila sifa ya FastAPI inapita kwa njia yao.

Kuelewa kwao ni muhimu kwa sababu inatoa **uhalali** otomatiki (muhimu kwa usalama na imara — kamwe usitake ingizo safi), uchambuzi/kutiwa lazima, uokoaji, na msaada wa hariri, yote kutoka darasa moja linalobainishwa.

Wanafanya kazi kama **chanzo kimoja cha ukweli**: muundo mmoja unasukuma uthalali wa ombi, umbo la jibu, na nyaraka za kuundwa kiotomatiki.

Hii aina-inayounganishwa, huhalali-kwa-kawaida njia — kupata uthalali imara wa ingizo na ujumbe wazi wa kosa hasa bure — ni sababu kuu kwa nini FastAPI ni kwa tija na salama, kuwa miundo ya Pydantic kisimu cha msingi, ujifunze lazima ujuzi.