{"title":"En-till-en-relationer","version":"6.1","locale":"sv","docname":"topics/db/examples/one_to_one","url":"/sv/6.1/topics/db/examples/one_to_one/","canonical":"https://djangodocs.dev/sv/6.1/topics/db/examples/one_to_one/","summary":"För att definiera en en-till-en-relation använder du OneToOneField . I detta exempel kan en Place valfritt vara en Restaurant : Code Copy from django.db import…","html":"

En-till-en-relationerLink to this heading#

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För att definiera en en-till-en-relation använder du OneToOneField.

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I detta exempel kan en Place valfritt vara en Restaurant:

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Code
from django.db import models\n\n\nclass Place(models.Model):\n    name = models.CharField(max_length=50)\n    address = models.CharField(max_length=80)\n\n    def __str__(self):\n        return f"{self.name} the place"\n\n\nclass Restaurant(models.Model):\n    place = models.OneToOneField(\n        Place,\n        on_delete=models.CASCADE,\n        primary_key=True,\n    )\n    serves_hot_dogs = models.BooleanField(default=False)\n    serves_pizza = models.BooleanField(default=False)\n\n    def __str__(self):\n        return "%s the restaurant" % self.place.name\n\n\nclass Waiter(models.Model):\n    restaurant = models.ForeignKey(Restaurant, on_delete=models.CASCADE)\n    name = models.CharField(max_length=50)\n\n    def __str__(self):\n        return "%s the waiter at %s" % (self.name, self.restaurant)\n
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Nedan följer exempel på operationer som kan utföras med hjälp av Python API-faciliteterna.

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Skapa ett par platser:

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Python console
>>> p1 = Place(name="Demon Dogs", address="944 W. Fullerton")\n>>> p1.save()\n>>> p2 = Place(name="Ace Hardware", address="1013 N. Ashland")\n>>> p2.save()\n
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Skapa en restaurang. Skicka objektet ”parent” som primärnyckel för detta objekt:

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Python console
>>> r = Restaurant(place=p1, serves_hot_dogs=True, serves_pizza=False)\n>>> r.save()\n
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En restaurang kan få tillgång till sin plats:

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Python console
>>> r.place\n<Place: Demon Dogs the place>\n
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En plats kan komma åt sin restaurang, om den finns tillgänglig:

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Python console
>>> p1.restaurant\n<Restaurant: Demon Dogs the restaurant>\n
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p2 har inte någon tillhörande restaurang:

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Python console
>>> from django.core.exceptions import ObjectDoesNotExist\n>>> try:\n...     p2.restaurant\n... except ObjectDoesNotExist:\n...     print("There is no restaurant here.")\n...\nThere is no restaurant here.\n
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Du kan också använda hasattr för att undvika att behöva fånga upp undantag:

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Python console
>>> hasattr(p2, "restaurant")\nFalse\n
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Ställ in platsen med hjälp av tilldelningsnotation. Eftersom place är primärnyckeln för Restaurant kommer sparandet att skapa en ny restaurang:

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Python console
>>> r.place = p2\n>>> r.save()\n>>> p2.restaurant\n<Restaurant: Ace Hardware the restaurant>\n>>> r.place\n<Place: Ace Hardware the place>\n
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Ställ tillbaka platsen igen och använd uppdraget i omvänd riktning:

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Python console
>>> p1.restaurant = r\n>>> p1.restaurant\n<Restaurant: Demon Dogs the restaurant>\n
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Observera att du måste spara ett objekt innan det kan tilldelas en en-till-en-relation. Om du t.ex. skapar en Restaurant med en osparad Place uppstår ValueError:

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Python console
>>> p3 = Place(name="Demon Dogs", address="944 W. Fullerton")\n>>> Restaurant.objects.create(place=p3, serves_hot_dogs=True, serves_pizza=False)\nTraceback (most recent call last):\n...\nValueError: save() prohibited to prevent data loss due to unsaved related object 'place'.\n
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Restaurant.objects.all() returnerar restaurangerna, inte platserna. Observera att det finns två restauranger - Ace Hardware the Restaurant skapades i anropet till r.place = p2:

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Python console
>>> Restaurant.objects.all()\n<QuerySet [<Restaurant: Demon Dogs the restaurant>, <Restaurant: Ace Hardware the restaurant>]>\n
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Place.objects.all() returnerar alla platser, oavsett om de har restauranger eller inte:

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Python console
>>> Place.objects.order_by("name")\n<QuerySet [<Place: Ace Hardware the place>, <Place: Demon Dogs the place>]>\n
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Du kan ställa frågor till modellerna med hjälp av lookups across relationships:

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Python console
>>> Restaurant.objects.get(place=p1)\n<Restaurant: Demon Dogs the restaurant>\n>>> Restaurant.objects.get(place__pk=1)\n<Restaurant: Demon Dogs the restaurant>\n>>> Restaurant.objects.filter(place__name__startswith="Demon")\n<QuerySet [<Restaurant: Demon Dogs the restaurant>]>\n>>> Restaurant.objects.exclude(place__address__contains="Ashland")\n<QuerySet [<Restaurant: Demon Dogs the restaurant>]>\n
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Detta fungerar även i omvänd ordning:

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Python console
>>> Place.objects.get(pk=1)\n<Place: Demon Dogs the place>\n>>> Place.objects.get(restaurant__place=p1)\n<Place: Demon Dogs the place>\n>>> Place.objects.get(restaurant=r)\n<Place: Demon Dogs the place>\n>>> Place.objects.get(restaurant__place__name__startswith="Demon")\n<Place: Demon Dogs the place>\n
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Om du tar bort en plats kommer dess restaurang att tas bort (förutsatt att OneToOneField definierades med on_delete inställd på CASCADE, vilket är standard):

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Python console
>>> p2.delete()\n(2, {'one_to_one.Restaurant': 1, 'one_to_one.Place': 1})\n>>> Restaurant.objects.all()\n<QuerySet [<Restaurant: Demon Dogs the restaurant>]>\n
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Lägg till en servitör i restaurangen:

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Python console
>>> w = r.waiter_set.create(name="Joe")\n>>> w\n<Waiter: Joe the waiter at Demon Dogs the restaurant>\n
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Fråga servitörerna:

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Python console
>>> Waiter.objects.filter(restaurant__place=p1)\n<QuerySet [<Waiter: Joe the waiter at Demon Dogs the restaurant>]>\n>>> Waiter.objects.filter(restaurant__place__name__startswith="Demon")\n<QuerySet [<Waiter: Joe the waiter at Demon Dogs the restaurant>]>\n
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