Django: I want to connect about one-to-many

Question

Django: I want to connect about one-to-many...

enter image description here

What should I do?

from django.db import models

class Note(models.Model)
    content = models.CharField(max_length=20)

class A(models.Model)
    name = models.CharField(max_length=20)
    addr = models.CharField(max_length=20)
    notes = models.ManyToManyField(Note) # ...? I don't know...

class B(models.Model)
    nickname = models.CharField(max_length=20)
    mobile = models.CharField(max_length=20)
    notes = models.ManyToManyField(Note) # ...? I don't know...

Note model : A model = 1 : N... Note model : B model = 1 : N...

I want to connect Note - A at the same time Note - B...

Please answer me!

Thank you!

Edit 130208 8:36 KST----

Maybe ForegienKey is available...

But my case can't use that.

Because if I want only connection(ex. Note to A), I can do it like the code below.

from django.db import models

class Note(models.Model)
    content = models.CharField(max_length=20)
    conn = models.ForeignKey(A)

class A(models.Model)
    name = models.CharField(max_length=20)
    addr = models.CharField(max_length=20)

But my case need two connection(Note - A, Note - B).

So.... I don't know what should I do...

I think that your graph contradicts your explanation... The N and the 1 in those links should be swapped if you want the models A and B to have several notes. — Adrián, Feb 07 '13 at 15:28
I find out https://docs.djangoproject.com/en/dev/ref/contrib/contenttypes/#django.contrib.contenttypes.generic.GenericForeignKey.... But still I don't know... — chobo, Feb 08 '13 at 07:10

Adrián · Accepted Answer · 2013-02-08T16:49:18.163

Use a models.ForeignKey.

If you want several notes for each instance of A and B you could try something like this:

from django.db import models

    class Note(models.Model):
        content = models.CharField(max_length=20)
        related_to = models.ForeignKey(A_or_B)

    class A_or_B(models.Model):
        pass

    class A(A_or_B):
        name = models.CharField(max_length=20)
        addr = models.CharField(max_length=20)

    class B(A_or_B):
        nickname = models.CharField(max_length=20)
        mobile = models.CharField(max_length=20)

searching the notes that belong to a particular A or B intance would be like this:

a = A(name="some_name", addr="somewhere")
a.save()
a_note = Note(content="blablabla", related_to=a.id)
a_note.save()
notes_related_to_a = Note.objects.filter(related_to=a.id)
links_from_notes_to_a = {note_x.related_to.a for note_x in notes_related_to_a}
if len(links_from_notes_to_a) and links_from_notes_to_a[0] == a:
    print "It works!"

the related_to attribute of the abstract parent class will have an attribute whose name is the uncapitalized name of the actual class of instance (a or b in this example). This attribute contains the instance of A or B from where you can access the right attributes.

Check this part of the documentation for more info.

@chobo just added how to add it – Adrián Feb 08 '13 at 12:51 — Adrián, Feb 08 '13 at 12:51

score 0 · Answer 2 · answered Feb 07 '13 at 15:48

Use ForeignKey

from django.db import models

class Note(models.Model)
    content = models.CharField(max_length=20)

class A(models.Model)
    name = models.CharField(max_length=20)
    addr = models.CharField(max_length=20)
    notes = models.ForeignKey(Note) # ...? I don't know...

class B(models.Model)
    nickname = models.CharField(max_length=20)
    mobile = models.CharField(max_length=20)
    notes = models.ForeignKey(Note) # ...? I don't know...

Django: I want to connect about one-to-many

2 Answers2