---
title: "Many-to-many relationships"
version: 2.1
locale: es
source: https://docs.djangoproject.com/es/2.1/topics/db/examples/many_to_many/
canonical: https://djangodocs.dev/es/2.1/topics/db/examples/many_to_many/
---
# Many-to-many relationships

To define a many-to-many relationship, use
[`ManyToManyField`](/es/2.1/ref/models/fields/#django.db.models.ManyToManyField).

In this example, an `Article` can be published in multiple `Publication`
objects, and a `Publication` has multiple `Article` objects:

```python
from django.db import models

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

    def __str__(self):
        return self.title

    class Meta:
        ordering = ('title',)

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

    def __str__(self):
        return self.headline

    class Meta:
        ordering = ('headline',)
```

What follows are examples of operations that can be performed using the Python
API facilities. Note that if you are using [an intermediate model](/es/2.1/topics/db/models/#intermediary-manytomany) for a many-to-many relationship, some of the related
manager’s methods are disabled, so some of these examples won’t work with such
models.

Create a few `Publications`:

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

Create an `Article`:

```pycon
>>> a1 = Article(headline='Django lets you build Web apps easily')
```

You can’t associate it with a `Publication` until it’s been saved:

```pycon
>>> a1.publications.add(p1)
Traceback (most recent call last):
...
ValueError: 'Article' instance needs to have a primary key value before a many-to-many relationship can be used.
```

Save it!

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

Associate the `Article` with a `Publication`:

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

Create another `Article`, and set it to appear in the `Publications`:

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

Adding a second time is OK, it will not duplicate the relation:

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

Adding an object of the wrong type raises [`TypeError`](https://docs.python.org/3/library/exceptions.html#TypeError):

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

Create and add a `Publication` to an `Article` in one step using
[`create()`](/es/2.1/ref/models/relations/#django.db.models.fields.related.RelatedManager.create):

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

`Article` objects have access to their related `Publication` objects:

```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>]>
```

`Publication` objects have access to their related `Article` objects:

```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>]>
```

Many-to-many relationships can be queried using [lookups across
relationships](/es/2.1/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>]>
```

The [`count()`](/es/2.1/ref/models/querysets/#django.db.models.query.QuerySet.count) function respects
[`distinct()`](/es/2.1/ref/models/querysets/#django.db.models.query.QuerySet.distinct) as well:

```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>]>
```

Reverse m2m queries are supported (i.e., starting at the table that doesn’t have
a [`ManyToManyField`](/es/2.1/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>]>
```

Excluding a related item works as you would expect, too (although the SQL
involved is a little complex):

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

If we delete a `Publication`, its `Articles` won’t be able to access it:

```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 []>
```

If we delete an `Article`, its `Publications` won’t be able to access it:

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

Adding via the “other” end of an 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>]>
```

Adding via the other end using keywords:

```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>]>
```

Removing `Publication` from an `Article`:

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

And from the other end:

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

Relation sets can be set:

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

Relation sets can be cleared:

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

And you can clear from the other end:

```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>]>
```

Recreate the `Article` and `Publication` we have deleted:

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

Bulk delete some `Publications` \- references to deleted publications should
go:

```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>]>
```

Bulk delete some articles - references to deleted objects should go:

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

After the [`delete()`](/es/2.1/ref/models/querysets/#django.db.models.query.QuerySet.delete), the
[`QuerySet`](/es/2.1/ref/models/querysets/#django.db.models.query.QuerySet) cache needs to be cleared, and the
referenced objects should be gone:

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