---
title: "Många-till-många-relationer"
version: 6.0
locale: sv
source: https://docs.djangoproject.com/sv/6.0/topics/db/examples/many_to_many/
canonical: https://djangodocs.dev/sv/6.0/topics/db/examples/many_to_many/
---
# Många-till-många-relationer

Om du vill definiera en relation mellan många och många använder du [`ManyToManyField`](/sv/6.0/ref/models/fields/#django.db.models.ManyToManyField).

I det här exemplet kan en ”artikel” publiceras i flera ”publikationsobjekt” och en ”publikation” har flera ”artikelobjekt”:

```python
from django.db import models

class Publication(models.Model):
    title = models.CharField(max_length=30)

    class Meta:
        ordering = ["title"]

    def __str__(self):
        return self.title

class Article(models.Model):
    headline = models.CharField(max_length=100)
    publications = models.ManyToManyField(Publication)

    class Meta:
        ordering = ["headline"]

    def __str__(self):
        return self.headline
```

Nedan följer exempel på operationer som kan utföras med hjälp av Python API-faciliteterna.

Skapa några instanser av typen `Publication`:

```pycon
>>> p1 = Publication(title="The Python Journal")
>>> p1.save()
>>> p2 = Publication(title="Science News")
>>> p2.save()
>>> p3 = Publication(title="Science Weekly")
>>> p3.save()
```

Skapa en `Artikel`:

```pycon
>>> a1 = Article(headline="Django lets you build web apps easily")
```

Du kan inte associera den med en `Publikation` förrän den har sparats:

```pycon
>>> a1.publications.add(p1)
Traceback (most recent call last):
...
ValueError: "<Article: Django lets you build web apps easily>" needs to have a value for field "id" before this many-to-many relationship can be used.
```

Spara det!

```pycon
>>> a1.save()
```

Koppla `Artikeln` till en `Publikation`:

```pycon
>>> a1.publications.add(p1)
```

Skapa en ny ”artikel” och ställ in den så att den visas i dess publikationer:

```pycon
>>> a2 = Article(headline="NASA uses Python")
>>> a2.save()
>>> a2.publications.add(p1, p2)
>>> a2.publications.add(p3)
```

Att lägga till en andra gång är OK, det kommer inte att duplicera relationen:

```pycon
>>> a2.publications.add(p3)
```

Att lägga till ett objekt av fel typ ger upphov till [`TypeError`](https://docs.python.org/3/library/exceptions.html#TypeError):

```pycon
>>> a2.publications.add(a1)
Traceback (most recent call last):
...
TypeError: 'Publication' instance expected
```

Skapa och lägg till en `Publikation` till en `Artikel` i ett steg med [`create()`](/sv/6.0/ref/models/relations/#django.db.models.fields.related.RelatedManager.create):

```pycon
>>> new_publication = a2.publications.create(title="Highlights for Children")
```

objekten `Article` har tillgång till sina relaterade objekt `Publication`:

```pycon
>>> a1.publications.all()
<QuerySet [<Publication: The Python Journal>]>
>>> a2.publications.all()
<QuerySet [<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]>
```

objekt av typen `Publication` har tillgång till sina relaterade objekt av typen `Article`:

```pycon
>>> p2.article_set.all()
<QuerySet [<Article: NASA uses Python>]>
>>> p1.article_set.all()
<QuerySet [<Article: Django lets you build web apps easily>, <Article: NASA uses Python>]>
>>> Publication.objects.get(id=4).article_set.all()
<QuerySet [<Article: NASA uses Python>]>
```

Många-till-många-relationer kan efterfrågas med hjälp av [lookups across relationships](/sv/6.0/topics/db/queries/#lookups-that-span-relationships):

```pycon
>>> Article.objects.filter(publications__id=1)
<QuerySet [<Article: Django lets you build web apps easily>, <Article: NASA uses Python>]>
>>> Article.objects.filter(publications__pk=1)
<QuerySet [<Article: Django lets you build web apps easily>, <Article: NASA uses Python>]>
>>> Article.objects.filter(publications=1)
<QuerySet [<Article: Django lets you build web apps easily>, <Article: NASA uses Python>]>
>>> Article.objects.filter(publications=p1)
<QuerySet [<Article: Django lets you build web apps easily>, <Article: NASA uses Python>]>

>>> Article.objects.filter(publications__title__startswith="Science")
<QuerySet [<Article: NASA uses Python>, <Article: NASA uses Python>]>

>>> Article.objects.filter(publications__title__startswith="Science").distinct()
<QuerySet [<Article: NASA uses Python>]>
```

Funktionen [`count()`](/sv/6.0/ref/models/querysets/#django.db.models.query.QuerySet.count) respekterar även [`distinct()`](/sv/6.0/ref/models/querysets/#django.db.models.query.QuerySet.distinct):

```pycon
>>> Article.objects.filter(publications__title__startswith="Science").count()
2

>>> Article.objects.filter(publications__title__startswith="Science").distinct().count()
1

>>> Article.objects.filter(publications__in=[1, 2]).distinct()
<QuerySet [<Article: Django lets you build web apps easily>, <Article: NASA uses Python>]>
>>> Article.objects.filter(publications__in=[p1, p2]).distinct()
<QuerySet [<Article: Django lets you build web apps easily>, <Article: NASA uses Python>]>
```

Omvända m2m-frågor stöds (dvs. börjar vid den tabell som inte har en [`ManyToManyField`](/sv/6.0/ref/models/fields/#django.db.models.ManyToManyField)):

```pycon
>>> Publication.objects.filter(id=1)
<QuerySet [<Publication: The Python Journal>]>
>>> Publication.objects.filter(pk=1)
<QuerySet [<Publication: The Python Journal>]>

>>> Publication.objects.filter(article__headline__startswith="NASA")
<QuerySet [<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]>

>>> Publication.objects.filter(article__id=1)
<QuerySet [<Publication: The Python Journal>]>
>>> Publication.objects.filter(article__pk=1)
<QuerySet [<Publication: The Python Journal>]>
>>> Publication.objects.filter(article=1)
<QuerySet [<Publication: The Python Journal>]>
>>> Publication.objects.filter(article=a1)
<QuerySet [<Publication: The Python Journal>]>

>>> Publication.objects.filter(article__in=[1, 2]).distinct()
<QuerySet [<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]>
>>> Publication.objects.filter(article__in=[a1, a2]).distinct()
<QuerySet [<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>, <Publication: The Python Journal>]>
```

Att utesluta ett relaterat objekt fungerar också som du förväntar dig (även om den SQL som används är lite komplicerad):

```pycon
>>> Article.objects.exclude(publications=p2)
<QuerySet [<Article: Django lets you build web apps easily>]>
```

Om vi tar bort en `Publication` kommer dess relaterade `Article`-instanser inte att kunna komma åt den:

```pycon
>>> p1.delete()
>>> Publication.objects.all()
<QuerySet [<Publication: Highlights for Children>, <Publication: Science News>, <Publication: Science Weekly>]>
>>> a1 = Article.objects.get(pk=1)
>>> a1.publications.all()
<QuerySet []>
```

Om vi tar bort en ”artikel” kommer dess relaterade ”publikationsinstanser” inte att kunna komma åt den:

```pycon
>>> a2.delete()
>>> Article.objects.all()
<QuerySet [<Article: Django lets you build web apps easily>]>
>>> p2.article_set.all()
<QuerySet []>
```

Lägga till via den ”andra” änden av en m2m:

```pycon
>>> a4 = Article(headline="NASA finds intelligent life on Earth")
>>> a4.save()
>>> p2.article_set.add(a4)
>>> p2.article_set.all()
<QuerySet [<Article: NASA finds intelligent life on Earth>]>
>>> a4.publications.all()
<QuerySet [<Publication: Science News>]>
```

Lägga till via den andra änden med hjälp av nyckelord:

```pycon
>>> new_article = p2.article_set.create(headline="Oxygen-free diet works wonders")
>>> p2.article_set.all()
<QuerySet [<Article: NASA finds intelligent life on Earth>, <Article: Oxygen-free diet works wonders>]>
>>> a5 = p2.article_set.all()[1]
>>> a5.publications.all()
<QuerySet [<Publication: Science News>]>
```

Ta bort `Publication` från en `Article`:

```pycon
>>> a4.publications.remove(p2)
>>> p2.article_set.all()
<QuerySet [<Article: Oxygen-free diet works wonders>]>
>>> a4.publications.all()
<QuerySet []>
```

Och från den andra änden:

```pycon
>>> p2.article_set.remove(a5)
>>> p2.article_set.all()
<QuerySet []>
>>> a5.publications.all()
<QuerySet []>
```

Relationssatser kan ställas in:

```pycon
>>> a4.publications.all()
<QuerySet [<Publication: Science News>]>
>>> a4.publications.set([p3])
>>> a4.publications.all()
<QuerySet [<Publication: Science Weekly>]>
```

Relationssatser kan rensas:

```pycon
>>> p2.article_set.clear()
>>> p2.article_set.all()
<QuerySet []>
```

Och du kan rensa från andra änden:

```pycon
>>> p2.article_set.add(a4, a5)
>>> p2.article_set.all()
<QuerySet [<Article: NASA finds intelligent life on Earth>, <Article: Oxygen-free diet works wonders>]>
>>> a4.publications.all()
<QuerySet [<Publication: Science News>, <Publication: Science Weekly>]>
>>> a4.publications.clear()
>>> a4.publications.all()
<QuerySet []>
>>> p2.article_set.all()
<QuerySet [<Article: Oxygen-free diet works wonders>]>
```

Återskapa den `Artikel` och `Publikation` som vi har tagit bort:

```pycon
>>> p1 = Publication(title="The Python Journal")
>>> p1.save()
>>> a2 = Article(headline="NASA uses Python")
>>> a2.save()
>>> a2.publications.add(p1, p2, p3)
```

Ta bort några `Publication`-instanser och referenserna till de borttagna publikationerna kommer inte längre att ingå i de relaterade posterna:

```pycon
>>> Publication.objects.filter(title__startswith="Science").delete()
>>> Publication.objects.all()
<QuerySet [<Publication: Highlights for Children>, <Publication: The Python Journal>]>
>>> Article.objects.all()
<QuerySet [<Article: Django lets you build web apps easily>, <Article: NASA finds intelligent life on Earth>, <Article: NASA uses Python>, <Article: Oxygen-free diet works wonders>]>
>>> a2.publications.all()
<QuerySet [<Publication: The Python Journal>]>
```

Bulkradera vissa artiklar - referenser till raderade objekt bör tas bort:

```pycon
>>> q = Article.objects.filter(headline__startswith="Django")
>>> print(q)
<QuerySet [<Article: Django lets you build web apps easily>]>
>>> q.delete()
```

Efter [`delete()`](/sv/6.0/ref/models/querysets/#django.db.models.query.QuerySet.delete) måste [`QuerySet`](/sv/6.0/ref/models/querysets/#django.db.models.query.QuerySet)-cachen rensas och de refererade objekten bör försvinna:

```pycon
>>> print(q)
<QuerySet []>
>>> p1.article_set.all()
<QuerySet [<Article: NASA uses Python>]>
```