Kif tmudellja r-relazzjonijiet fl-ORM?

Question

Accepted Answer

Django's ORM tmudellja t-tliet relazzjonijiet fundamentali tad-database bi tipid ta' field dedikati: **ForeignKey** (one-to-many), **ManyToManyField** (many-to-many), u **OneToOneField** (one-to-one). Dawn jiddefinixxu kif it-tabelli huma relatati u jagħtuk aċċess Pythonic għal oġġetti relatati.

## ForeignKey — one-to-many (l-aktar komuni)

```python
class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    title = models.CharField(max_length=200)
    author = models.ForeignKey(
        Author,
        on_delete=models.CASCADE,        # what happens if the author is deleted
        related_name="books",            # access the reverse: author.books
    )
```

```python
# access related objects naturally:
book.author                # the Author this book belongs to (forward)
author.books.all()         # all Books by this author (reverse, via related_name)
```

`ForeignKey` tmudellja "ħafna kotba jappartjenu lill-awtur wieħed." Il-komportament ta' `on_delete` (`CASCADE`, `PROTECT`, `SET_NULL`, eċċ.) huwa **meħtieġ** u jiddefinixxi x'jiġri l-kotba jekk l-awtur jiġi mħassar.

## ManyToManyField — many-to-many

```python
class Article(models.Model):
    title = models.CharField(max_length=200)
    tags = models.ManyToManyField("Tag", related_name="articles")   # many tags ↔ many articles

class Tag(models.Model):
    name = models.CharField(max_length=50)
```

```python
article.tags.add(tag1, tag2)        # associate tags
article.tags.all()                   # all tags on this article
tag.articles.all()                   # all articles with this tag (reverse)
```

Django tautomatikament toħloq it-**tabella ta' join** wara `ManyToManyField` — int sempliċement tuża `.add()`, `.remove()`, `.all()`. (Għal dejta addizzjonali fuq ir-relazzjoni, uża mudell ta' `through`.)

## OneToOneField — one-to-one

```python
class User(models.Model):
    username = models.CharField(max_length=50)

class Profile(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)   # one profile per user
    bio = models.TextField()
```

`OneToOneField` tenfurza link stratt one-to-one — ħafna drabi tintuża biex testendi mudell (eż. Profile li testendi User).

## `on_delete` options (importanti biex tagħżel b'mod korrett)

```text
CASCADE   → delete related objects too (delete author → delete their books)
PROTECT   → prevent deletion if related objects exist (raises an error)
SET_NULL  → set the FK to NULL (requires null=True) — keep the books, orphan them
SET_DEFAULT / SET(...) → set to a default/computed value
RESTRICT  → similar to PROTECT, with nuances
```

## Interrogazzjoni fuq relazzjonijiet

```python
# traverse relationships in queries with __ (double underscore)
Book.objects.filter(author__name="Tolkien")        # books whose author's name is Tolkien
Article.objects.filter(tags__name="python")         # articles tagged 'python'
```

## Għaliex hu importanti

Il-mudelljar korrett tal-relazzjonijiet hu fundamentali għat-tħaddim mad-data relazzjonali f'Django — kważi kull applikazzjoni reali għandha entitajiet relatati (users u posts, orders u items, articles u tags), allura l-fehim tat-tliet tipid ta' relationship field hu għarfien essenzjali ta' kuljum.
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ForeignKey — one-to-many (l-aktar komuni)

ManyToManyField — many-to-many

OneToOneField — one-to-one

on_delete options (importanti biex tagħżel b'mod korrett)

Interrogazzjoni fuq relazzjonijiet

Għaliex hu importanti

`on_delete` options (importanti biex tagħżel b'mod korrett)