{"title":"一対一 (one-to-one) 関係","version":"5.0","locale":"ja","docname":"topics/db/examples/one_to_one","url":"/ja/5.0/topics/db/examples/one_to_one/","canonical":"https://djangodocs.dev/ja/5.0/topics/db/examples/one_to_one/","summary":"一対一の関係を定義するには、OneToOneField を使用します。","html":"

一対一 (one-to-one) 関係Link to this heading#

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一対一の関係を定義するには、OneToOneField を使用します。

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この例では、 Place は任意で Restaurant になることができます:

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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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以下は、Python API の機能を使って実行できる操作の例です。

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2つの Place を作成する:

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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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レストランを作成する。オブジェクトの主キーとして "parent" オブジェクトを渡します:

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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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Restaurant は自身の place にアクセスできます:

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Python console
>>> r.place\n<Place: Demon Dogs the place>\n
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Place は自身の restaurant に、利用可能ならアクセスできます:

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Python console
>>> p1.restaurant\n<Restaurant: Demon Dogs the restaurant>\n
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p2 には関連付けられたレストランがありません:

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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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また、 hasattr を使えば、例外キャッチが不要になります:

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Python console
>>> hasattr(p2, "restaurant")\nFalse\n
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代入記法を使用して place をセットします。place は Restaurant のプライマリキーなので、保存すると新しい restaurant が作成されます:

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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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また、place を逆方向の割り当てを使用してセットします:

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Python console
>>> p1.restaurant = r\n>>> p1.restaurant\n<Restaurant: Demon Dogs the restaurant>\n
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オブジェクトを1対1のリレーションシップに割り当てるには、オブジェクトを保存する必要があることに注意してください。例えば、保存されていない Place で Restaurant を作成すると ValueError が発生します:

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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() は Place のセットではなく、 Restaurant のセットを返します。レストランが2つあることに注意してください - "Ace Hardware" は r.place = p2 の呼び出しで作成されたレストランです:

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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() は、Restaurant を持つかどうかに関係なく、すべての Place を返します:

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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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リレーションを横断するルックアップ を使ってモデルをクエリできます:

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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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これは逆方向にも機能します:

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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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場所を削除した場合、そのレストランは削除されます (OneToOneField が on_delete にデフォルトの CASCADE をセットして定義されていると仮定した場合):

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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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Restaurant に Waiter を追加します:

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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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waiter にクエリします:

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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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