What is the Django ORM and how to query data?

Question

Accepted Answer

**Django ORM** translates Python code to **SQL queries**.

```python
from .models import Article, User

# Get all articles
articles = Article.objects.all()

# Filter
published = Article.objects.filter(published=True)
by_author = Article.objects.filter(author__name="Alice")

# Exclude
drafts = Article.objects.exclude(published=True)

# Get single object
article = Article.objects.get(id=1)  # Raises exception if not found
article = Article.objects.filter(id=1).first()  # Returns None

# Ordering
articles = Article.objects.order_by("-created_at")

# Chaining
results = (
    Article.objects
    .filter(published=True)
    .order_by("-created_at")
    .select_related("author")
    .only("title", "author__name")
)

# Aggregation
from django.db.models import Count, Avg
stats = Article.objects.aggregate(
    count=Count("id"),
    avg_views=Avg("views_count")
)

# Q objects for complex queries
from django.db.models import Q
articles = Article.objects.filter(
    Q(title__icontains="python") | Q(content__icontains="django")
)
```

**Performance tips:**
- `select_related()` — JOIN for ForeignKey.
- `prefetch_related()` — separate query for ManyToMany.
- `only()` — select specific columns.
- `defer()` — exclude specific columns.

Python: What is the Django ORM and how to query data?