{"title":"Hubungan banyak-ke-satu","version":"3.1","locale":"id","docname":"topics/db/examples/many_to_one","url":"/id/3.1/topics/db/examples/many_to_one/","canonical":"https://djangodocs.dev/id/3.1/topics/db/examples/many_to_one/","summary":"Untuk menentukan hubungan many-to-one, gunakan ForeignKey : Code Copy from django.db import models class Reporter ( models . Model ): first_name = models .…","html":"

Hubungan banyak-ke-satuLink to this heading#

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Untuk menentukan hubungan many-to-one, gunakan ForeignKey:

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Code
from django.db import models\n\nclass Reporter(models.Model):\n    first_name = models.CharField(max_length=30)\n    last_name = models.CharField(max_length=30)\n    email = models.EmailField()\n\n    def __str__(self):\n        return "%s %s" % (self.first_name, self.last_name)\n\nclass Article(models.Model):\n    headline = models.CharField(max_length=100)\n    pub_date = models.DateField()\n    reporter = models.ForeignKey(Reporter, on_delete=models.CASCADE)\n\n    def __str__(self):\n        return self.headline\n\n    class Meta:\n        ordering = ['headline']\n
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Apa yang mengikuti adalah contoh-contoh dari tindakan yang dapat dilakukan menggunakan fasilitas API Python.

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Buat sedikir Reporter:

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Python console
>>> r = Reporter(first_name='John', last_name='Smith', email='john@example.com')\n>>> r.save()\n\n>>> r2 = Reporter(first_name='Paul', last_name='Jones', email='paul@example.com')\n>>> r2.save()\n
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Buat sebuah Artikel:

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Python console
>>> from datetime import date\n>>> a = Article(id=None, headline="This is a test", pub_date=date(2005, 7, 27), reporter=r)\n>>> a.save()\n\n>>> a.reporter.id\n1\n\n>>> a.reporter\n<Reporter: John Smith>\n
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Catat bahwa anda harus menyimpan sebuah obyek sebelum itu dapat diberikan ke hubungan foreign key. Sebagai contoh, membuat Article dengan Reporter tidak disimpan memunculkan ValueError:

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Python console
>>> r3 = Reporter(first_name='John', last_name='Smith', email='john@example.com')\n>>> Article.objects.create(headline="This is a test", pub_date=date(2005, 7, 27), reporter=r3)\nTraceback (most recent call last):\n...\nValueError: save() prohibited to prevent data loss due to unsaved related object 'reporter'.\n
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Obyek artikel mempunyai akses ke obyek Reporter terkait:

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Python console
>>> r = a.reporter\n
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Buat sebuah Article melalui obyek Reporter:

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Python console
>>> new_article = r.article_set.create(headline="John's second story", pub_date=date(2005, 7, 29))\n>>> new_article\n<Article: John's second story>\n>>> new_article.reporter\n<Reporter: John Smith>\n>>> new_article.reporter.id\n1\n
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Buat sebuah artikel baru:

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Python console
>>> new_article2 = Article.objects.create(headline="Paul's story", pub_date=date(2006, 1, 17), reporter=r)\n>>> new_article2.reporter\n<Reporter: John Smith>\n>>> new_article2.reporter.id\n1\n>>> r.article_set.all()\n<QuerySet [<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>]>\n
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Tambah artikel sama ke kumpulan artikel berbeda - periksa bahwa itu berpindah:

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Python console
>>> r2.article_set.add(new_article2)\n>>> new_article2.reporter.id\n2\n>>> new_article2.reporter\n<Reporter: Paul Jones>\n
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Menambahkan sebuah obyek dari jenis salah memunculkan TypeError:

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Python console
>>> r.article_set.add(r2)\nTraceback (most recent call last):\n...\nTypeError: 'Article' instance expected, got <Reporter: Paul Jones>\n\n>>> r.article_set.all()\n<QuerySet [<Article: John's second story>, <Article: This is a test>]>\n>>> r2.article_set.all()\n<QuerySet [<Article: Paul's story>]>\n\n>>> r.article_set.count()\n2\n\n>>> r2.article_set.count()\n1\n
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Catat bahwa di contoh terakhir artikel telah dipindahkan dari John ke Paul.

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Pengelola terkait mendukung pencarian bidang-bidang juga. API otomatis mengikuti hubungan sejauh anda butuhkan. Gunakan garis bawah ganda untuk memisahkan hubungan. Ini bekerja sebanyak tingkatan yang anda inginkan. Tidak ada batasan. Sebagai contoh:

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Python console
>>> r.article_set.filter(headline__startswith='This')\n<QuerySet [<Article: This is a test>]>\n\n# Find all Articles for any Reporter whose first name is "John".\n>>> Article.objects.filter(reporter__first_name='John')\n<QuerySet [<Article: John's second story>, <Article: This is a test>]>\n
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Benar-benar cocok tersirat disini:

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Python console
>>> Article.objects.filter(reporter__first_name='John')\n<QuerySet [<Article: John's second story>, <Article: This is a test>]>\n
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Permintaan dua kali lebih bidang terkait. Ini menterjemahkan pada sebuah keadaan AND dalam klausa WHERE:

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Python console
>>> Article.objects.filter(reporter__first_name='John', reporter__last_name='Smith')\n<QuerySet [<Article: John's second story>, <Article: This is a test>]>\n
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Untuk pencarian terkait anda dapat menyediakan sebuah nilai primary key atau lewatkan obyek terkait dengan tegas:

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Python console
>>> Article.objects.filter(reporter__pk=1)\n<QuerySet [<Article: John's second story>, <Article: This is a test>]>\n>>> Article.objects.filter(reporter=1)\n<QuerySet [<Article: John's second story>, <Article: This is a test>]>\n>>> Article.objects.filter(reporter=r)\n<QuerySet [<Article: John's second story>, <Article: This is a test>]>\n\n>>> Article.objects.filter(reporter__in=[1,2]).distinct()\n<QuerySet [<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>]>\n>>> Article.objects.filter(reporter__in=[r,r2]).distinct()\n<QuerySet [<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>]>\n
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Anda dapat juga menggunakan queryset daripada daftar harfiah dari instance:

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Python console
>>> Article.objects.filter(reporter__in=Reporter.objects.filter(first_name='John')).distinct()\n<QuerySet [<Article: John's second story>, <Article: This is a test>]>\n
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Meminta di arah berlawanan:

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Python console
>>> Reporter.objects.filter(article__pk=1)\n<QuerySet [<Reporter: John Smith>]>\n>>> Reporter.objects.filter(article=1)\n<QuerySet [<Reporter: John Smith>]>\n>>> Reporter.objects.filter(article=a)\n<QuerySet [<Reporter: John Smith>]>\n\n>>> Reporter.objects.filter(article__headline__startswith='This')\n<QuerySet [<Reporter: John Smith>, <Reporter: John Smith>, <Reporter: John Smith>]>\n>>> Reporter.objects.filter(article__headline__startswith='This').distinct()\n<QuerySet [<Reporter: John Smith>]>\n
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Menghitung dalam arah berlawanan bekerja dalam hubungan dengan distinct():

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Python console
>>> Reporter.objects.filter(article__headline__startswith='This').count()\n3\n>>> Reporter.objects.filter(article__headline__startswith='This').distinct().count()\n1\n
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Permintaan dapat berputar seperti lingkaran:

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Python console
>>> Reporter.objects.filter(article__reporter__first_name__startswith='John')\n<QuerySet [<Reporter: John Smith>, <Reporter: John Smith>, <Reporter: John Smith>, <Reporter: John Smith>]>\n>>> Reporter.objects.filter(article__reporter__first_name__startswith='John').distinct()\n<QuerySet [<Reporter: John Smith>]>\n>>> Reporter.objects.filter(article__reporter=r).distinct()\n<QuerySet [<Reporter: John Smith>]>\n
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If you delete a reporter, their articles will be deleted (assuming that the\nForeignKey was defined with django.db.models.ForeignKey.on_delete set to\nCASCADE, which is the default):

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Python console
>>> Article.objects.all()\n<QuerySet [<Article: John's second story>, <Article: Paul's story>, <Article: This is a test>]>\n>>> Reporter.objects.order_by('first_name')\n<QuerySet [<Reporter: John Smith>, <Reporter: Paul Jones>]>\n>>> r2.delete()\n>>> Article.objects.all()\n<QuerySet [<Article: John's second story>, <Article: This is a test>]>\n>>> Reporter.objects.order_by('first_name')\n<QuerySet [<Reporter: John Smith>]>\n
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Anda dapat menghapus menggunakan JOIN di permintaan:

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Python console
>>> Reporter.objects.filter(article__headline__startswith='This').delete()\n>>> Reporter.objects.all()\n<QuerySet []>\n>>> Article.objects.all()\n<QuerySet []>\n
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