使用JOIN表达式转换查询以及与Django ORM的通用关系

class Business(models.Model):
    manager = models.ForeignKey(User, on_delete=models.CASCADE)
    #...

class Event(models.Model):
    business = models.ForeignKey(Business, on_delete=models.CASCADE)

    text = models.TextField()
    when = models.DateTimeField()
    likes = GenericRelation('Like')

class Like(models.Model):
    person = models.ForeignKey(User, on_delete=models.CASCADE)

    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id')

    date = models.DateTimeField(auto_now=True)
class Business(models.Model):
    manager = mod