Models na ORM zinafanyaje kazi?

Question

Accepted Answer

**Model** ni class ya Python inayofafanua muundo wa data yako — kila model inapangiliwa na table ya database, na kila attribute na column. **ORM (Object-Relational Mapper)** inakuruhusu kuingiliana na database ukitumia objects na methods za Python badala ya kuandika raw SQL.

## Kufafanua model

```python
from django.db import models

class Article(models.Model):
    title = models.CharField(max_length=200)       # → VARCHAR column
    body = models.TextField()                        # → TEXT column
    published = models.BooleanField(default=False)
    created_at = models.DateTimeField(auto_now_add=True)  # set on creation
    views = models.IntegerField(default=0)

def __str__(self):
        return self.title                            # readable representation (admin, shell)
```

Kila field ya model inapangiliwa na column ya database yenye aina inayofaa. Kuendesha migrations kunaunda table inayolingana — hauandiki `CREATE TABLE` wewe mwenyewe kamwe.

## CRUD kwa ORM (bila SQL)

```python
# CREATE
article = Article.objects.create(title="Hello", body="...")

# READ — query with Python methods
Article.objects.all()                            # all rows → SELECT *
Article.objects.get(id=1)                         # one row by primary key
Article.objects.filter(published=True)            # WHERE published = true
Article.objects.filter(title__icontains="django") # WHERE title ILIKE '%django%'
Article.objects.exclude(views=0).order_by("-created_at")  # complex queries, chained

# UPDATE
article.title = "Updated"
article.save()
Article.objects.filter(published=False).update(published=True)  # bulk update

# DELETE
article.delete()
```

ORM inatafsiri miito hii ya Python kuwa SQL kiotomatiki. Field lookups (`__icontains`, `__gte`, `__in`, n.k.) zinaeleza masharti ya WHERE kwa njia ya Python.

## Kwa nini ORM? Faida na mbadala

```text
✓ Write database code in Python — no SQL, more readable, less error-prone
✓ Database-agnostic — the same code works on PostgreSQL, MySQL, SQLite
✓ SECURITY — parameterized queries by default → prevents SQL injection
✓ Integrates with migrations, admin, forms (define the model once)
⚠️ Trade-off: can generate inefficient queries (e.g. N+1) if used carelessly —
   sometimes you need select_related/prefetch_related or raw SQL for complex cases
```

## Models ni chanzo kimoja cha ukweli (DRY)

```text
One model definition drives: the database schema (migrations), the admin interface,
ModelForms, and serializers (DRF) — define it once, reuse everywhere.
```

## Kwa nini ni muhimu

Models na ORM ni kitovu cha Django — ndizo jinsi unavyofafanua na kufanya kazi na data ya programu yako, ambayo ni moyo wa programu nyingi za wavuti.

Kuzielewa ni maarifa ya msingi ya kila siku: models zinafafanua muundo wa data yako (zikipangilia classes na tables, attributes na columns) na zinatumika kama **chanzo kimoja cha ukweli** kinachoendesha schema ya database, interface ya admin, forms, na serializers za API (falsafa ya DRY).

ORM inakuruhusu kuandika operesheni za database katika **Python safi na inayosomeka badala ya SQL**, ikiwa na faida kubwa: uhamishikaji wa database (code ileile inakimbia kwenye database tofauti), uunganishaji mkubwa na sehemu nyingine za Django, na muhimu zaidi **usalama** (inatumia parameterized queries kwa chaguo-msingi, ikizuia SQL injection).

Kujua jinsi ya kufafanua models zenye fields zinazofaa, kufanya operesheni za CRUD, na kuhoji kwa syntax ya lookup ya ORM ni jambo la msingi kwa kujenga programu yoyote ya Django.

Muhimu sawa ni ufahamu wa **mbadala** wa ORM — kwamba queries rahisi zinaweza kuwa zisizofaa (tatizo la N+1) bila uangalifu — ambayo inaongoza kwenye mbinu za uboreshaji.

Tabaka la model/ORM ndipo programu za Django zinatumia mantiki yake nyingi, kuifanya kuwa nyenzo ya msingi na ya lazima kuimudu.