Django中间模型中的访问字段 [英] Access fields in Django intermediate model

问题描述

我正在按照中间层模型的Django文档中所述创建人员组和成员资格.

I'm creating a Person Group and Membership as described in Django docs for intermediate model.

class Person(models.Model):
  name = models.CharField(max_length=128)

  def __unicode__(self):
    return self.name

class Group(models.Model):
  name = models.CharField(max_length=128)
  members = models.ManyToManyField(Person, through='Membership')

  def __unicode__(self):
    return self.name

class Membership(models.Model):
  person = models.ForeignKey(Person)
  group = models.ForeignKey(Group)
  date_joined = models.DateField()
  invite_reason = models.CharField(max_length=64)

可以通过以下方式从组"对象访问人":

It is possible to access the Person from a Group object with:

>>>Group.members.name

Django是否创建另一个查询以获取Person?我可以从组对象访问 date_joined 字段吗?

Does Django creates another query to fetch the Person? Can I access the date_joined field from a Group object?

让我感到困惑的是，我希望得到人名"字段:

The thing that confuses me is that I would expect to get the Person name field with:

>>>Group.members.person.name

如果一个人有一个字段名称"，并且中间模型也有一个字段名称"，会发生什么情况.

What happens if a Person has a field 'name' and also the intermediate model have a field 'name'.

推荐答案

示例中的member字段是ManyToManyField，因此它是一种访问许多人而不是一个人的方法.成员字段下的对象实际上是一种特殊类型的Manager，而不是Person:

The members field in your example is a ManyToManyField, so it's a way to access many people rather than one person. The object that is under the members field is actually a special type of Manager, not a Person:

>>> print my_group.members
<django.db.models.fields.related.ManyRelatedManager object at 0x181f7d0>

要更好地了解经理是什么，请请参阅文档.

To understand better what a Manager is, see the documentation.

例如，要访问一个人的名字，请执行以下操作:

To access a person's name you would do for example:

>>> for person in my_group.members.all():
>>>     print person.name

您无法通过Manager的member字段访问Membership模型中的字段.要访问其中的任何字段，您可以执行以下操作:

You cannot access the fields in your Membership model via the Manager in the members field. To access any of the fields in it you would do:

>>> for membership in my_group.membership_set.all():
>>>     print membership.date_joined

因此，如果您的成员资格模型中有一个名为name的字段，则可以按以下方式访问它:

And so if you had a field called name in your Membership model, you would access it like this:

>>> for membership in my_group.membership_set.all():
>>>     print membership.name

访问人员姓名的第二种方法是:

A second way to access a Person's name would be:

>>> for membership in my_group.membership_set.all():
>>>     print membership.person.name

请注意， membership_set 是指向成员资格的管理者的默认名称，但是可以通过在相应的外键中指定 related_name 来更改.例如，如果从 Membership 到 Group 的外键的定义如下:

Note that membership_set is a default name for the manager pointing towards the membership, but it can be changed by specifying related_name in the corresponding foreign key. For example if the foreign key from the Membership to the Group would be defined like such:

    group = models.ForeignKey(Group, related_name="group_members")

然后，您将使用 group_members 来访问管理器:

Then you would access the manager using group_members:

>>> for membership in my_group.group_members.all():
>>>     print membership.name

希望能有所帮助:)

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