Untuk menentukan hubungan satu-ke-satu, gunakan OneToOneField
.
Dalam contoh ini, sebuah pilihan Place
dapat menjadi sebuah Restaurant
:
from django.db import models
class Place(models.Model):
name = models.CharField(max_length=50)
address = models.CharField(max_length=80)
def __str__(self): # __unicode__ on Python 2
return "%s the place" % self.name
class Restaurant(models.Model):
place = models.OneToOneField(
Place,
on_delete=models.CASCADE,
primary_key=True,
)
serves_hot_dogs = models.BooleanField(default=False)
serves_pizza = models.BooleanField(default=False)
def __str__(self): # __unicode__ on Python 2
return "%s the restaurant" % self.place.name
class Waiter(models.Model):
restaurant = models.ForeignKey(Restaurant, on_delete=models.CASCADE)
name = models.CharField(max_length=50)
def __str__(self): # __unicode__ on Python 2
return "%s the waiter at %s" % (self.name, self.restaurant)
What follows are examples of operations that can be performed using the Python API facilities.
Buat sepasang Place:
>>> p1 = Place(name='Demon Dogs', address='944 W. Fullerton')
>>> p1.save()
>>> p2 = Place(name='Ace Hardware', address='1013 N. Ashland')
>>> p2.save()
Create a Restaurant. Pass the ID of the “parent” object as this object’s ID:
>>> r = Restaurant(place=p1, serves_hot_dogs=True, serves_pizza=False)
>>> r.save()
Sebuah Restaurant dapat mengakses tempatnya:
>>> r.place
<Place: Demon Dogs the place>
Sebuah Place dapat mengakses restorannya, jika tersedia:
>>> p1.restaurant
<Restaurant: Demon Dogs the restaurant>
p2 tidak mempunyai restoran terkait:
>>> from django.core.exceptions import ObjectDoesNotExist
>>> try:
>>> p2.restaurant
>>> except ObjectDoesNotExist:
>>> print("There is no restaurant here.")
There is no restaurant here.
You can also use hasattr
to avoid the need for exception catching:
>>> hasattr(p2, 'restaurant')
False
Set the place using assignment notation. Because place is the primary key on Restaurant, the save will create a new restaurant:
>>> r.place = p2
>>> r.save()
>>> p2.restaurant
<Restaurant: Ace Hardware the restaurant>
>>> r.place
<Place: Ace Hardware the place>
Set the place back again, using assignment in the reverse direction:
>>> p1.restaurant = r
>>> p1.restaurant
<Restaurant: Demon Dogs the restaurant>
Note that you must save an object before it can be assigned to a one-to-one
relationship. For example, creating a Restaurant
with unsaved Place
raises ValueError
:
>>> p3 = Place(name='Demon Dogs', address='944 W. Fullerton')
>>> Restaurant.objects.create(place=p3, serves_hot_dogs=True, serves_pizza=False)
Traceback (most recent call last):
...
ValueError: save() prohibited to prevent data loss due to unsaved related object 'place'.
Previously, saving an object with unsaved related objects did not raise an error and could result in silent data loss. In 1.8-1.8.3, unsaved model instances couldn’t be assigned to related fields, but this restriction was removed to allow easier usage of in-memory models.
Restaurant.objects.all() just returns the Restaurants, not the Places. Note that there are two restaurants - Ace Hardware the Restaurant was created in the call to r.place = p2:
>>> Restaurant.objects.all()
[<Restaurant: Demon Dogs the restaurant>, <Restaurant: Ace Hardware the restaurant>]
Place.objects.all() mengembalikan semua Places, tanpa memperhatikan apakah mereka mempunyai Restaurants:
>>> Place.objects.order_by('name')
[<Place: Ace Hardware the place>, <Place: Demon Dogs the place>]
You can query the models using lookups across relationships:
>>> Restaurant.objects.get(place=p1)
<Restaurant: Demon Dogs the restaurant>
>>> Restaurant.objects.get(place__pk=1)
<Restaurant: Demon Dogs the restaurant>
>>> Restaurant.objects.filter(place__name__startswith="Demon")
[<Restaurant: Demon Dogs the restaurant>]
>>> Restaurant.objects.exclude(place__address__contains="Ashland")
[<Restaurant: Demon Dogs the restaurant>]
This of course works in reverse:
>>> Place.objects.get(pk=1)
<Place: Demon Dogs the place>
>>> Place.objects.get(restaurant__place=p1)
<Place: Demon Dogs the place>
>>> Place.objects.get(restaurant=r)
<Place: Demon Dogs the place>
>>> Place.objects.get(restaurant__place__name__startswith="Demon")
<Place: Demon Dogs the place>
Add a Waiter to the Restaurant:
>>> w = r.waiter_set.create(name='Joe')
>>> w
<Waiter: Joe the waiter at Demon Dogs the restaurant>
Query the waiters:
>>> Waiter.objects.filter(restaurant__place=p1)
[<Waiter: Joe the waiter at Demon Dogs the restaurant>]
>>> Waiter.objects.filter(restaurant__place__name__startswith="Demon")
[<Waiter: Joe the waiter at Demon Dogs the restaurant>]
Agt 01, 2016