51

我正在尝试创建一个消息系统，其中消息的发件人和收件人可以是通用实体。这对发件人来说似乎很好，只有对象可以引用（GenericForeignKey），但我不知道如何为收件人解决这个问题（GenericManyToManyKey ??）

下面是一个简化的例子。PersonClient 和 CompanyClient 从 Client 继承属性，但有自己的特定细节。最后一行是症结所在。如何让消息接收者成为一组 CompanyClients 和 PersonClients

  class Client(models.Model):
      city = models.CharField(max_length=16)

      class Meta:
          abstract = True

  class PersonClient(Client):
      first_name = models.CharField(max_length=16)
      last_name = models.CharField(max_length=16)
      gender = models.CharField(max_length=1)

  class CompanyClient(Client):
      name = models.CharField(max_length=32)
      tax_no = PositiveIntegerField()

  class Message(models.Model):
      msg_body = models.CharField(max_length=1024)
      sender = models.ForeignKey(ContentType)
      recipients = models.ManyToManyField(ContentType)
4

3 回答 3

63

您可以通过手动创建消息和收件人之间的联结表来使用通用关系来实现这一点：

from django.db import models
from django.contrib.contenttypes import generic
from django.contrib.contenttypes.models import ContentType

class Client(models.Model):
    city = models.CharField(max_length=16)

    # These aren't required, but they'll allow you do cool stuff
    # like "person.sent_messages.all()" to get all messages sent
    # by that person, and "person.received_messages.all()" to
    # get all messages sent to that person.
    # Well...sort of, since "received_messages.all()" will return
    # a queryset of "MessageRecipient" instances.
    sent_messages = generic.GenericRelation('Message',
        content_type_field='sender_content_type',
        object_id_field='sender_id'
    )
    received_messages = generic.GenericRelation('MessageRecipient',
        content_type_field='recipient_content_type',
        object_id_field='recipient_id'
    )

    class Meta:
        abstract = True

class PersonClient(Client):
    first_name = models.CharField(max_length=16)
    last_name = models.CharField(max_length=16)
    gender = models.CharField(max_length=1)

    def __unicode__(self):
        return u'%s %s' % (self.last_name, self.first_name)

class CompanyClient(Client):
    name = models.CharField(max_length=32)
    tax_no = models.PositiveIntegerField()

    def __unicode__(self):
        return self.name

class Message(models.Model):
    sender_content_type = models.ForeignKey(ContentType)
    sender_id = models.PositiveIntegerField()
    sender = generic.GenericForeignKey('sender_content_type', 'sender_id')
    msg_body = models.CharField(max_length=1024)

    def __unicode__(self):
        return u'%s...' % self.msg_body[:25]

class MessageRecipient(models.Model):
    message = models.ForeignKey(Message)
    recipient_content_type = models.ForeignKey(ContentType)
    recipient_id = models.PositiveIntegerField()
    recipient = generic.GenericForeignKey('recipient_content_type', 'recipient_id')

    def __unicode__(self):
        return u'%s sent to %s' % (self.message, self.recipient)

您可以像这样使用上述模型：

>>> person1 = PersonClient.objects.create(first_name='Person', last_name='One', gender='M')
>>> person2 = PersonClient.objects.create(first_name='Person', last_name='Two', gender='F')
>>> company = CompanyClient.objects.create(name='FastCompany', tax_no='4220')
>>> company_ct = ContentType.objects.get_for_model(CompanyClient)
>>> person_ct = ContentType.objects.get_for_model(person1) # works for instances too.

# now we create a message:

>>> msg = Message.objects.create(sender_content_type=person_ct, sender_id=person1.pk, msg_body='Hey, did any of you move my cheese?')

# and send it to a coupla recipients:

>>> MessageRecipient.objects.create(message=msg, recipient_content_type=person_ct, recipient_id=person2.pk)
>>> MessageRecipient.objects.create(message=msg, recipient_content_type=company_ct, recipient_id=company.pk)
>>> MessageRecipient.objects.count()
2

如您所见，这是一个更加冗长（复杂？）的解决方案。我可能会保持简单，并在下面使用 Prariedogg 的解决方案。

于 2009-06-02T00:10:47.300 回答
10

解决这个问题的绝对最佳方法是使用一个名为 django-gm2m 的库

pip install django-gm2m

那么如果我们有我们的模型

>>> from django.db import models
>>>
>>> class Video(models.Model):
>>>       class Meta:
>>>           abstract = True
>>>
>>> class Movie(Video):
>>>     pass
>>>
>>> class Documentary(Video):
>>>     pass

还有一个用户

>>> from gm2m import GM2MField
>>>
>>> class User(models.Model):
>>>     preferred_videos = GM2MField()

我们能做的

>>> user = User.objects.create()
>>> movie = Movie.objects.create()
>>> documentary = Documentary.objects.create()
>>>
>>> user.preferred_videos.add(movie)
>>> user.preferred_videos.add(documentary)

甜吗？

有关更多信息，请访问此处：

http://django-gm2m.readthedocs.org/en/stable/quick_start.html

于 2015-10-07T10:13:16.453 回答
7

您可以通过简化架构以包含一个Client带有标志的表来解决此问题，以指示它是什么类型的客户端，而不是使用两个单独的模型。

from django.db import models
from django.utils.translation import ugettext_lazy as _

class Client(models.Model):
    PERSON, CORPORATION = range(2)
    CLIENT_TYPES = (
                    (PERSON, _('Person')),
                    (CORPORATION, _('Corporation')),
                   )
    type = models.PositiveIntegerField(choices=CLIENT_TYPES, default=PERSON)
    city = models.CharField(max_length=16)
    first_name = models.CharField(max_length=16, blank=True, null=True)
    last_name = models.CharField(max_length=16, blank=True, null=True)
    corporate_name = models.CharField(max_length=16, blank=True, null=True)
    tax_no = models.PositiveIntegerField(blank=True, null=True)

    def save(self, *args, **kwargs):
        """
        Does some validation ensuring that the person specific fields are
        filled in when self.type == self.PERSON, and corporation specific
        fields are filled in when self.type == self.CORPORATION ...

        """
        # conditional save logic goes here
        super(Client, self).save(*args, **kwargs)

如果您以这种方式做事，您可能根本不必使用通用外键。作为额外的便利，您还可以为 Client 模型编写自定义管理器，例如Client.corporate.all(), Client.person.all()，以返回仅包含您想要的客户端类型的预过滤查询集。

这也可能不是解决问题的最佳方式。我只是把它作为一种潜在的可能性扔在那里。我不知道是否有将两个相似模型组合在一起并使用保存覆盖来确保数据完整性的传统智慧。似乎它可能存在潜在问题......我会让社区在这个方面向我学习。

于 2009-06-01T02:02:47.063 回答