通用的多对多关系

  • Z时代
  • 2024-01-10
  • 分类：问答

我正在尝试创建一个消息传递系统，其中消息的发送者和接收者可以是通用实体。对于发件人来说，这似乎很好，在该发件人中只有要引用的对象（GenericForeignKey），但我不知道如何为收件人进行处理（GenericManyToManyKey ??）。

下面是一个简化的示例。PersonClient和CompanyClient从Client继承属性，但具有其自己的特定详细信息。最后一行是症结所在。如何允许邮件收件人成为CompanyClients和PersonClients的集合

  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)

回答：

你可以通过手动创建消息和收件人之间的连接表来使用通用关系来实现此目的：

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)

你将像这样使用以上模型：

>>> 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

如你所见，这是一个更为冗长（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。

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