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Django 6.1
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Caidrimh go leor

Chun caidreamh go leor a shainiú, bain úsáid as: class: ~django.db.models.manyToManyField.

Sa sampla seo, is féidir Airteag a fhoilsiú i rudaí éagsúla Foilseacháin ``, agus tá rudaí ``Airteag iolracha ag Foilsiúcháin:

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

Seo a leanas samplaí d'oibríochtaí is féidir a dhéanamh ag baint úsáide as na háiseanna API Python.

Create a few Publication instances:

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

Cruthaigh Airteag:

Python console
>>> a1 = Article(headline="Django lets you build web apps easily")

Ní féidir leat é a cheangal le ``Foilsiúcháin ``go dtí go sábhálfar é:

Python console
>>> 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.

Sábháil é!

Python console
>>> a1.save()

Comhcheangail an Airteag le Foilseachán `:

Python console
>>> a1.publications.add(p1)

Create another Article, and set it to appear in its publications:

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

Tá sé ceart go leor an dara huair a chur leis, ní dhúbailfidh sé an gaol:

Python console
>>> a2.publications.add(p3)

Ardaíonn réad den chineál mícheart leis: exc: TypeError:

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

Cruthaigh agus cuir Foilseachán le Airteag` i gcéim amháin ag baint úsáid:meth: ~Django.db.Models.Fields.Related.RelatedManager.Create:

Python console
>>> new_publication = a2.publications.create(title="Highlights for Children")

Tá rochtain ag rudaí Airteag ar a gcuid rudaí gaolmhara ``Foilsiúcháin ``:

Python console
>>> 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>]>

Tá rochtain ag rudaí Foilseacha ar a gcuid rudaí gaolmhara Airteag:

Python console
>>> 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>]>

<lookups-that-span-relationships>Is féidir caidrimh go leor a cheistiú ag baint úsáidea:ref: `cuardaigh thar fud caidrimh `:

Python console
>>> 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>]>

Féachann an fheidhm: Meth: ~django.db.models.query.queryset.count: meth: ~django.db.models.query.queryset.Distinct chomh maith:

Python console
>>> 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>]>

Tacaítear le ceisteanna m2m ar ais (ie, ag tosú ag an tábla nach bhfuil a:class: ~django.db.models.manyToManyField):

Python console
>>> 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>]>

Oibríonn mír gaolmhar a eisiamh mar a bheadh ag súil leat freisin (cé go bhfuil an SQL atá i gceist beagán casta):

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

If we delete a Publication, its related Article instances won't be able to access it:

Python console
>>> 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 related Publication instances won't be able to access it:

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

Ag cur leis trí fhoirceann 'eile' m2m:

Python console
>>> 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>]>

Ag cur leis an gceann eile ag úsáid eochairfhocail:

Python console
>>> 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>]>

“Foilseachán” a bhaint as Airteag:

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

Agus ón gceann eile:

Python console
>>> p2.article_set.remove(a5)
>>> p2.article_set.all()
<QuerySet []>
>>> a5.publications.all()
<QuerySet []>

Is féidir tacair chaidrimh a shocrú:

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

Is féidir tacair chaidrimh a ghlanadh:

Python console
>>> p2.article_set.clear()
>>> p2.article_set.all()
<QuerySet []>

Agus is féidir leat a ghlanadh ón gceann eile:

Python console
>>> 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>]>

Athchruthaigh an Airteag agus Foilsiúna atá scriosta againn:

Python console
>>> 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 Publication instances, and the references to deleted publications will no longer be included in the related entries:

Python console
>>> 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>]>

Scrios mórchóir roinnt alt - ba chóir tagairtí do rudaí scriosta dul:

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

Tar éis an: meth: ~django.db.models.query.queryset.delete, ní mór taisce an:class: ~django.db.models.queryset a ghlanadh, agus ba chóir na rudaí tagartha a bheith imithe:

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

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