CODEWITHSUNDEEP
djangodjango-models
vts
vts

Reputation: 911

get extra field value in Django's many-to-many relationship

In Django's many-to-many relationships extra fields, we can add extra fields, as the code below (from https://docs.djangoproject.com/en/dev/topics/db/models/#intermediary-manytomany), my question is how could I get the extra field easily, is it possible to not query on the intermediary table directly? the exactly example is:

>>> ringo = Person.objects.create(name="Ringo Starr")
>>> paul = Person.objects.create(name="Paul McCartney")
>>> beatles = Group.objects.create(name="The Beatles")
>>> m1 = Membership(person=ringo, group=beatles,
...     date_joined=date(1962, 8, 16),
...     invite_reason="Needed a new drummer.")
>>> m1.save()
>>> beatles.members.all()
[<Person: Ringo Starr>]

>>> p = beatles.members.all()[0]
>>> p
[<Person: Ringo Starr>]

I want to get the date_joined value of p, I know it can be done by

>>> Membership.objects.get(person=p, group=beatles).date_joined
datetime.date(1962, 8, 16)

but is it possible to get it simply just like:

>>> p.xxx(*args)

=============== models.py ================

from django.db import models

class Person(models.Model):
    name = models.CharField(max_length=128)

    def __str__(self):              # __unicode__ on Python 2
        return self.name

class Group(models.Model):
    name = models.CharField(max_length=128)
    members = models.ManyToManyField(Person, through='Membership')

    def __str__(self):              # __unicode__ on Python 2
        return self.name

class Membership(models.Model):
    person = models.ForeignKey(Person)
    group = models.ForeignKey(Group)
    date_joined = models.DateField()
    invite_reason = models.CharField(max_length=64)

Upvotes: 1

Views: 2455

Answers (1)

Paulo Almeida
Paulo Almeida

Reputation: 8071

From the documentation page you link to:

Another way to access the same information is by querying the many-to-many reverse relationship from a Person object:

>>> ringos_membership = ringo.membership_set.get(group=beatles)
>>> ringos_membership.date_joined
datetime.date(1962, 8, 16)
>>> ringos_membership.invite_reason
'Needed a new drummer.'

Upvotes: 1

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