---
title: "关系对象参考"
version: 3.0
locale: zh-hans
source: https://docs.djangoproject.com/zh-hans/3.0/ref/models/relations/
canonical: https://djangodocs.dev/zh-hans/3.0/ref/models/relations/
---
# 关系对象参考

#### `class RelatedManager`

“关系管理器”是一个用于处理“一对多”和“多对多”关联关系的管理器。在以下两种情况用到：

- “另一边”的关联关系 [`ForeignKey`](/zh-hans/3.0/ref/models/fields/#django.db.models.ForeignKey)。即:

  ```
  from django.db import models

  class Reporter(models.Model):
      # ...
      pass

  class Article(models.Model):
      reporter = models.ForeignKey(Reporter, on_delete=models.CASCADE)
  ```

  在上面的例子中，以下方法会在管理器 `reporter.article_set` 中可用。
- 双边关系 [`ManyToManyField`](/zh-hans/3.0/ref/models/fields/#django.db.models.ManyToManyField)

  ```
  class Topping(models.Model):
      # ...
      pass

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

  在这个例子中，下文列出的方法在 `topping.pizza_set` 和 `pizza.toppings` 中均可用。

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

将特定的模型对象加入关联对象集合。

举例:

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

上述例子中，由于有 [`ForeignKey`](/zh-hans/3.0/ref/models/fields/#django.db.models.ForeignKey) 关联关系，才可以使用 [`QuerySet.update()`](/zh-hans/3.0/ref/models/querysets/#django.db.models.query.QuerySet.update) 更新数据。这要求对象事先已经被保存在数据库内了。

你可以使用 `bulk=False` 参数让关系管理器通过调用 `e.save()` 来执行更新操作。

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()`](/zh-hans/3.0/ref/models/querysets/#django.db.models.query.QuerySet.bulk_create). If you need to execute
some custom logic when a relationship is created, listen to the
[`m2m_changed`](/zh-hans/3.0/ref/signals/#django.db.models.signals.m2m_changed) signal, which will
trigger `pre_add` and `post_add` actions.

Using `add()` on a relation that already exists won't duplicate the
relation, but it will still trigger signals.

For many-to-many relationships `add()` accepts either model instances
or field values, normally primary keys, as the `*objs` argument.

Use the `through_defaults` argument to specify values for the new
[intermediate model](/zh-hans/3.0/topics/db/models/#intermediary-manytomany) instance(s), if
needed.

> **Changed in Django 2.2**
>
> The `through_defaults` argument was added.

#### `create(through_defaults=None, **kwargs)`

创建一个新对象，保存至数据库，并将其放入关联对象集合内。返回刚创建的对象:

```
>>> 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.
```

This is equivalent to (but simpler than):

```
>>> 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)
```

无需指定定义了模型间关系的关键字参数。在上述例子中，我们并未向 `create()` 传递参数 `blog`。Django 知道要将新 `Entry` 对象的 `blog` 字段设置为 `b`。

Use the `through_defaults` argument to specify values for the new
[intermediate model](/zh-hans/3.0/topics/db/models/#intermediary-manytomany) instance, if
needed.

> **Changed in Django 2.2**
>
> The `through_defaults` argument was added.

#### `remove(*objs, bulk=True)`

从关系集合中移除特定的对象:

```
>>> 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()`](#django.db.models.fields.related.RelatedManager.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()`](/zh-hans/3.0/ref/models/querysets/#django.db.models.query.QuerySet.delete) which
means no model `save()` methods are called; listen to the
[`m2m_changed`](/zh-hans/3.0/ref/signals/#django.db.models.signals.m2m_changed) signal if you wish to
execute custom code when a relationship is deleted.

For many-to-many relationships `remove()` accepts either model
instances or field values, normally primary keys, as the `*objs`
argument.

For [`ForeignKey`](/zh-hans/3.0/ref/models/fields/#django.db.models.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`](/zh-hans/3.0/ref/models/fields/#django.db.models.ForeignKey) doesn't have
`null=True`, this is invalid.

For [`ForeignKey`](/zh-hans/3.0/ref/models/fields/#django.db.models.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`](/zh-hans/3.0/ref/signals/#django.db.models.signals.pre_save) and
[`post_save`](/zh-hans/3.0/ref/signals/#django.db.models.signals.post_save) signals and comes at the
expense of performance.

For many-to-many relationships, the `bulk` keyword argument doesn't
exist.

#### `clear(bulk=True)`

清空关系集合:

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

Note this doesn't delete the related objects -- it just disassociates
them.

Just like `remove()`, `clear()` is only available on
[`ForeignKey`](/zh-hans/3.0/ref/models/fields/#django.db.models.ForeignKey)s where `null=True` and it also
accepts the `bulk` keyword argument.

For many-to-many relationships, the `bulk` keyword argument doesn't
exist.

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

Replace the set of related objects:

```
>>> 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.

For [`ForeignKey`](/zh-hans/3.0/ref/models/fields/#django.db.models.ForeignKey) objects, the `bulk`
argument is passed on to [`add()`](#django.db.models.fields.related.RelatedManager.add) and [`remove()`](#django.db.models.fields.related.RelatedManager.remove).

For many-to-many relationships, the `bulk` keyword argument doesn't
exist.

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()`.

For many-to-many relationships `set()` accepts a list of either model
instances or field values, normally primary keys, as the `objs`
argument.

Use the `through_defaults` argument to specify values for the new
[intermediate model](/zh-hans/3.0/topics/db/models/#intermediary-manytomany) instance(s), if
needed.

> **Changed in Django 2.2**
>
> The `through_defaults` argument was added.

> **Note**
>
> 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.
>
> If you use [`prefetch_related()`](/zh-hans/3.0/ref/models/querysets/#django.db.models.query.QuerySet.prefetch_related),
> the `add()`, `remove()`, `clear()`, and `set()` methods clear
> the prefetched cache.