自定义可链接查询集

Question

这是我的一段代码

from django.db import models
from django.db.models.query import QuerySet
from mptt.models import MPTTModel
from base.models import Content, OrderedContent


class ArgumentQuerySet(QuerySet):
    def statements_with_count(self, *args, **kwargs):
        from statement.models import Statement
        statements = Statement.objects.none()
        result = self
        for node in result:
            statements_node = Statement.objects.filter( arguments__in = node.get_descendants(include_self = True), *args, **kwargs ).distinct()
            statements |= statements_node
            setattr(node, 'count', statements_node.count())
        statements = statements.distinct()
        setattr(result, 'statements', statements)
        setattr(result, 'count', statements.count())
        return result


class ArgumentManager(models.Manager):
    def get_query_set(self):
        return ArgumentQuerySet(self.model)


class Argument(MPTTModel, OrderedContent):
    parent = models.ForeignKey('self', null=True, blank=True)
    objects = ArgumentManager()

    class MPTTMeta:
        parent_attr = 'parent'
        order_insertion_by = ['weight', 'title', ]

    def __unicode__(self):
        return self.title

以下命令给了我关注的结果

a = Argument.objects.filter( title__icontains = 'function' )
b = a.statements_with_count()

否则，以下命令不起作用

c = Argument.objects.get( id = 514 )
d = c.get_children()
e = d.statements_with_count()

我该如何解决这个问题？

Answer 1

MPTT 使用 TreeManager 实例作为 get_children，它返回一个 models.query.Queryset，而不是您的自定义子类。您应该执行以下操作：

argument = Argument.objects.get(id = 514)
children_ids = [a.pk for a in argument.get_children()]
result = Argument.objects.filter(pk__in=children_ids).statements_with_count()

请注意，您的statements_with_count方法的性能不是很好，因为它将导致每个对象产生一个额外的数据库计数。