获取跨越关系的对象数

Question

我试图得到跨越关系的对象数。每个测试计划包含n个案例。方法plan\u case\u count（）给出了计数。每个TestPlanCase包含n个步骤。我想得到与计划相关的所有案例的所有步骤的总数。方法plan_case_step_count（）应该通过迭代查询集并将计数相加来实现这一点。但它不起作用。我收到的错误消息是：

“RelatedManager”对象没有属性“testplanstep\u set”

class TestPlan(models.Model):
    tp_title = models.CharField(max_length=200)
    tp_version = models.IntegerField()
    tp_date = models.DateField(default=timezone.now)

    def plan_case_count(self):
        """This one works"""
        return self.testplancase_set.count()

    def plan_case_step_count(self):
        """This one doesn't"""
        pcs_count = 0
        for case in self.testplancase_set:
            pcs_count += case.testplanstep_set.count()
        return pcs_count


class TestPlanCase(models.Model):
    tpc_plan = models.ForeignKey(TestPlan, on_delete=models.CASCADE)
    tpc_case = models.ForeignKey(TestCase, on_delete=models.CASCADE)
    tpc_seq_no = models.IntegerField(default=1)


class TestPlanStep(models.Model):
    tps_case =  models.ForeignKey(TestPlanCase, on_delete=models.CASCADE)
    tps_step = models.ForeignKey(TestSteps, on_delete=models.CASCADE)
    tps_ok =  models.CharField(max_length=4, choices=Choices.yes_no)
    tps_issue = models.CharField(max_length=200, blank=True)

我做错了什么

Answer 1

请直接编写计数查询：

def plan_case_step_count(self):
    return TestPlanStep.objects.filter(tps_case__tpc_plan=self).count()

这将直接用JOIN在SQL中编写COUNT(*)查询