Relationships

Following relationships “backward”

OneToOneField

class EntryDetail(models.Model):
    entry = models.OneToOneField(Entry)
    details = models.TextField()

e = Entry.objects.get(id=2)
e.entrydetail # returns the related EntryDetail object

Foreign Key

e.g. For these models:

class Blog(models.Model):
    name = models.CharField(max_length=100)

class Entry(models.Model):
    blog = models.ForeignKey(Blog)
    headline = models.CharField(max_length=255)

…the entries for a blog can be retrieved by using the name of the model for the foreign key, converted to lower-case with _set appended:

>>> b = Blog.objects.get(id=1)
>>> b.entry_set.all()

Note:

The _set manager returns a standard query set which can be manipulated in the normal way.
See the note ref related_name below…

Many to Many

The model that defines the ManyToManyField uses the attribute name of that field itself, whereas the “reverse” model uses the lowercased model name of the original model, plus ‘_set’ (just like reverse one-to-many relationships) e.g:

e = Entry.objects.get(id=3)
e.authors.all() # Returns all Author objects for this Entry.
e.authors.count()
e.authors.filter(name__contains='John')

a = Author.objects.get(id=5)
a.entry_set.all() # Returns all Entry objects for this Author.

Note: Like ForeignKey, ManyToManyField can specify related_name. In the above example, if the ManyToManyField in Entry had specified related_name='entries', then each Author instance would have an entries attribute instead of entry_set.