Django通用外键反向过滤器

Question

我有一个名为“Comments”的模型，它使用通用外键：

class CommentManager(models.Manager):

    def for_model(self, model):
        """
        QuerySet for all comments for a particular model (either an instance or
        a class).
        """
        ct = ContentType.objects.get_for_model(model)
        qs = self.get_query_set().filter(content_type=ct)
        if isinstance(model, models.Model):
            qs = qs.filter(object_pk=force_text(model._get_pk_val()))
        return qs


class Comment(models.Model):
    """
    A user comment about some object.
    """
    status = models.CharField(max_length=12, blank=True, null=True)
    sub_status = models.CharField(max_length=500, blank=True, null=True)
    comment = models.TextField()

    content_type = models.ForeignKey(
        ContentType,
        verbose_name=_('content type'),
        related_name="content_type_set_for_%(class)s")
    object_pk = models.TextField(_('object ID'))
    content_object = generic.GenericForeignKey(ct_field="content_type",
                                               fk_field="object_pk")

你可以放 cmets 的东西之一是Tickets：

class Ticket(CommonModel):
    type = models.ForeignKey(TicketType)
    priority = models.PositiveSmallIntegerField()
    status = models.ForeignKey(TicketStatus)
    access_serial_number = models.PositiveSmallIntegerField(null=True)
    parent = models.ForeignKey('self', null=True, related_name='child')
    submitted = models.DateTimeField()

我对@9​​87654324@ 做了很多过滤——过去我对门票的评论所做的只是当我显示Ticket 时，我使用Comments.objects.for_model(ticket) 来查找它的所有评论。但现在我想做的是找到Tickets 在评论中有特定文本。没有comment_set 或GenericForeignKey 的等价物。

这是我想出的，但它非常可怕：

comment_ticket_ids = [int(c.object_pk) for c in Comment.objects.for_model(Ticket).filter(comment__icontains='error')]
tickets = Ticket.filter(status=open_status, id__in=comment_ticket_ids)

一定有更好的办法。

Answer 1

也许您可以使用.extra() 添加一些内容来提供帮助。而不是

comment_ticket_ids = [int(c.object_pk) for c in Comment.objects.for_model(Ticket).filter(comment__icontains='error')]
tickets = Ticket.filter(status=open_status, id__in=comment_ticket_ids)

您可以附加字段id_wanted：

extra_select = {
 'id_wanted': 'CASE WHEN (SELECT COUNT(*) FROM tickets WHERE comments something) > 0 THEN TRUE ELSE FALSE END'
}

然后使用额外的选择过滤票证：

tickets = Tickets.objects.filter(ticket__status=open_status, id_wanted__isnull=False).extra(extra_select)

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我不完全清楚为什么不能在这两个模型之间建立 FKey 关系。