通用的多对多关系

Question

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.这对于发件人来说似乎很好,其中只有引用对象(GenericForeignKey),但我无法弄清楚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,但具有自己的特定详细信息.最后一行是关键点.如何允许邮件收件人成为一组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)

Answer 1

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实现此目的:

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)

您可以像上面这样使用上述模型:

>>> 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,这是一个更冗长(复杂？)的解决方案.我可能会保持简单,并使用上面的Prariedogg解决方案.

Answer 2

绝对最好的方法是使用名为django-gm2m的库

pip install django-gm2m

然后,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

和一个用户

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

我们可以做的

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

好吧？

欲了解更多信息,请访问:

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

Answer 3

您可以通过简化模式来包含Client带有标志的单个表来指示它是什么类型的客户端,而不是具有两个单独的模型.

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)

如果你以这种方式做事,你可能根本不需要使用通用外键.作为一个增加的方便,你也可以写为客户定制模型管理器如Client.corporate.all(),Client.person.all(),返回包含只想要客户端类型预过滤的查询集.

这也可能不是解决问题的最佳方法.我只是把它扔出去作为一种潜在的可能性.我不知道是否有关于将两个相似模型粉碎在一起并使用保存覆盖以确保数据完整性的传统智慧.看起来它可能有问题...我会让社区在这个上学习我.