Acuan obyek terkait

class RelatedManager

A "related manager" is a manager used in a one-to-many or many-to-many related context. This happens in two cases:

• "other side" dari sebuah hubungan ForeignKey. Yaitu:

  from django.db import models
  
  class Reporter(models.Model):
      # ...
      pass
  
  class Article(models.Model):
      reporter = models.ForeignKey(Reporter, on_delete=models.CASCADE)
  

  Dalam contoh diatas, metode-metode dibawah akan tersedia pada pengelola reporter.article_set.

• Kedua sisi dari hubungan ManyToManyField:

  class Topping(models.Model):
      # ...
      pass
  
  class Pizza(models.Model):
      toppings = models.ManyToManyField(Topping)
  

  Dalam contoh ini, metode-metode dibawah akan tersedia kedua pada topping.pizza_set dan pada pizza.toppings.

add(*objs, bulk=True, through_defaults=None)

Menambahkan obyek model ditentukan ke kumpulan obyek terkait.

Contoh:

>>> b = Blog.objects.get(id=1)
>>> e = Entry.objects.get(id=234)
>>> b.entry_set.add(e) # Associates Entry e with Blog b.

Dalam contoh diatas, dalam kasus hubungan ForeignKey, QuerySet.update() digunakan untuk melakukan pembaharuan. Ini membutuhkan obyek-obyek untuk sudah disimpan.

Anda dapat menggunakan argumen bulk=False daripada memiliki pengelola terkait melakukan pembaharuan dengan memanggil e.save().

Using add() with a many-to-many relationship, however, will not call any save() methods (the bulk argument doesn't exist), but rather create the relationships using QuerySet.bulk_create(). If you need to execute some custom logic when a relationship is created, listen to the m2m_changed signal, which will trigger pre_add and post_add actions.

Menggunakan ada() pada hubungan yang sudah ada tidak akan menggandakan hubungan, tetapi itu akan masih memicu sinyal.

add() also accepts the field the relation points to as an argument. The above example can be rewritten as b.entry_set.add(234).

Use the through_defaults argument to specify values for the new intermediate model instance(s), if needed.

Changed in Django 2.2:

The through_defaults argument was added.

create(through_defaults=None, **kwargs)

Membuat sebuah obyek baru, menyimpan itu dan menaruh itu dalam kumpulan obyek terkait. Mengembalikan obyek yang baru dibuat:

>>> b = Blog.objects.get(id=1)
>>> e = b.entry_set.create(
...     headline='Hello',
...     body_text='Hi',
...     pub_date=datetime.date(2005, 1, 1)
... )

# No need to call e.save() at this point -- it's already been saved.

Ini adalah setara pada (tetapi lebih sederhana dari):

>>> b = Blog.objects.get(id=1)
>>> e = Entry(
...     blog=b,
...     headline='Hello',
...     body_text='Hi',
...     pub_date=datetime.date(2005, 1, 1)
... )
>>> e.save(force_insert=True)

Note that there's no need to specify the keyword argument of the model that defines the relationship. In the above example, we don't pass the parameter blog to create(). Django figures out that the new Entry object's blog field should be set to b.

Use the through_defaults argument to specify values for the new intermediate model instance, if needed.

Changed in Django 2.2:

The through_defaults argument was added.

remove(*objs, bulk=True)

memindahkan pbyek-obyek model tertentu dari kumpulan obyek terkait:

>>> b = Blog.objects.get(id=1)
>>> e = Entry.objects.get(id=234)
>>> b.entry_set.remove(e) # Disassociates Entry e from Blog b.

Similar to add(), e.save() is called in the example above to perform the update. Using remove() with a many-to-many relationship, however, will delete the relationships using QuerySet.delete() which means no model save() methods are called; listen to the m2m_changed signal if you wish to execute custom code when a relationship is deleted.

Similarly to add(), remove() also accepts the field the relation points to as an argument. The above example can be rewritten as b.entry_set.remove(234).

For ForeignKey objects, this method only exists if null=True. If the related field can't be set to None (NULL), then an object can't be removed from a relation without being added to another. In the above example, removing e from b.entry_set() is equivalent to doing e.blog = None, and because the blog ForeignKey doesn't have null=True, this is invalid.

For ForeignKey objects, this method accepts a bulk argument to control how to perform the operation. If True (the default), QuerySet.update() is used. If bulk=False, the save() method of each individual model instance is called instead. This triggers the pre_save and post_save signals and comes at the expense of performance.

Untuk hubungan many-to-many, argumen kata kunci bulk tidak ada.

clear(bulk=True)

Memindahkan semua obyek dari kumpulan obyek terkait:

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

Catat ini tidak menghapus obyek-obyek terkait -- itu hanya memisahkan mereka.

Just like remove(), clear() is only available on ForeignKeys where null=True and it also accepts the bulk keyword argument.

Untuk hubungan many-to-many, argumen kata kunci bulk tidak ada.

set(objs, bulk=True, clear=False, through_defaults=None)

Ganti kumpulan dari obyek terkait:

>>> new_list = [obj1, obj2, obj3]
>>> e.related_set.set(new_list)

This method accepts a clear argument to control how to perform the operation. If False (the default), the elements missing from the new set are removed using remove() and only the new ones are added. If clear=True, the clear() method is called instead and the whole set is added at once.

Untuk obyek ForeignKey, argumen bulk dilewatkan ke add() dan remove().

Untuk hubungan many-to-many, argumen kata kunci bulk tidak ada.

Note that since set() is a compound operation, it is subject to race conditions. For instance, new objects may be added to the database in between the call to clear() and the call to add().

Similarly to add(), set() also accepts the field the relation points to as an argument. The above example can be rewritten as e.related_set.set([obj1.pk, obj2.pk, obj3.pk]).

Use the through_defaults argument to specify values for the new intermediate model instance(s), if needed.

Changed in Django 2.2:

The through_defaults argument was added.

Catatan

Note that add(), create(), remove(), clear(), and set() all apply database changes immediately for all types of related fields. In other words, there is no need to call save() on either end of the relationship.

Jika anda menggunakan prefetch_related(), metode add(), remove(), clear(), dan set() memberishkan cache yang terambil.