Question

content_type = ContentType.objects.get_for_model(Map)

    maps = maps.extra(select=SortedDict([
        ('member_count', MEMBER_COUNT_SQL),
        ('topic_count', TOPIC_COUNT_SQL),
    ]), select_params=(content_type.id,))

，ContentType为：

class ContentType(models.Model):
    name = models.CharField(max_length=100)
    app_label = models.CharField(max_length=100)
    model = models.CharField(_('python model class name'), max_length=100)
    objects = ContentTypeManager()

    class Meta:
        verbose_name = _('content type')
        verbose_name_plural = _('content types')
        db_table = 'django_content_type'
        ordering = ('name',)
        unique_together = (('app_label', 'model'),)

    def __unicode__(self):
        return self.name

    def model_class(self):
        "Returns the Python model class for this type of content."
        from django.db import models
        return models.get_model(self.app_label, self.model)

    def get_object_for_this_type(self, **kwargs):
        """
        Returns an object of this type for the keyword arguments given.
        Basically, this is a proxy around this object_type's get_object() model
        method. The ObjectNotExist exception, if thrown, will not be caught,
        so code that calls this method should catch it.
        """
        return self.model_class()._default_manager.using(self._state.db).get(**kwargs)

    def natural_key(self):
        return (self.app_label, self.model)

我想知道：用于??

的'content_type'是什么

Answer 1

它用于generic relations等等。

Answer 2

ContentType用于表示您希望使用许多不同模型具有外键并且能够在单个查询中获取所有模型的模型。

例如：你有一个城市模型，还有餐厅模型和一个酒吧模型。

要获得该市的所有餐厅和酒吧需要2个查询，

city.restaurant_set.all()
city.pub_set.all()

通过使用Generic外键，您可以将其设为单个查询，您可以从文档中查看：http://docs.djangoproject.com/en/dev/ref/contrib/contenttypes/#ref-contrib-contenttypes

什么是'content_type'的意思

2 个答案: