Django:无法使用预取计算属性进行注释

Question

目标是在给定的时间范围内对每个员工的工作时间进行汇总和注释。
楷模:

class Employee(models.Model):
    first_name = models.CharField(max_length=64)

class WorkTime(models.Model):
    employee = models.ForeignKey(Employee, on_delete=models.CASCADE, related_name="work_times")

    work_start = models.DateTimeField()
    work_end = models.DateTimeField()
    work_delta = models.IntegerField(default=0)

    def save(self, *args, **kwargs):
        self.work_delta = (self.work_end - self.work_start).seconds
        super().save(*args, **kwargs)

获取给定日期范围内每位员工的工作时间:

queryset = Employee.objects.prefetch_related(
                Prefetch(
                    'work_times',
                    queryset=WorkTime.objects.filter(work_start__date__range=("2021-03-01", "2021-03-15"]))
                        .order_by("work_start"),
                    to_attr="filtered_work_times"
                )).all()

尝试为每个员工注释 work_delta 的总和:

queryset.annotate(work_sum=Sum("filtered_work_times__work_delta"))

这会导致 FieldError:

Cannot resolve keyword 'filtered_work_times' into field. Choices are: first_name, id, work_times

从这里如何进行？顺便说一句，使用 Django 3.1。

Answer 1

您应该使用 filtering on annotations .
我没有尝试过，但我认为以下代码可能对您有所帮助:

from django.db.models import Sum, Q

Employee.objects.annotate(
    work_sum=Sum(
        'work_times__work_delta',
        filter=Q(work_times__work_start__date__range=["2021-03-01", "2021-03-15"])
    )
)