Django 在 Trunc 的 kind 属性中使用字段

我在我的项目中使用了PostgreSQL，并且有三个相关的模型:

class Timer(models.Model):
    start = models.DateTimeField()
    end = models.DateTimeField()
    task = models.ForeignKey(
        Task,
        models.CASCADE,
        related_name="timers",
    )

class Task(models.Model):
    name = models.CharField(max_length=64)
    wanted_duration = models.DurationField()
    frequency = models.ForeignKey(
        Frequency,
        models.CASCADE,
        related_name="tasks",
    )


class Frequency(models.Model):
    class TimeUnitChoices(models.TextChoices):
        DAY = "day", "day"
        WEEK = "week", "week"
        MONTH = "month", "month"
        QUARTER = "quarter", "quarter"
        YEAR = "year", "year"

    events_number = models.PositiveIntegerField()
    time_unit = models.CharField(max_length=32, choices=TimeUnitChoices.choices
    )

我想得到一个开始的时间跨度(天，周-一个频率的值time_unit)根据start日期(计时器的字段).

我try 执行下一个代码:task.timers.annotate(start_of=Trunc('start', kind='task__frequency__time_unit'))

但是Django不接受Trunc类的kind参数中的字段.错误:psycopg.ProgrammingError: cannot adapt type 'F' using placeholder '%t' (format: TEXT)

如果我在原始SQL中执行以下查询:

SELECT
DATE_TRUNC(schedules_frequency.time_unit, timers_timer.start)::date as start_of
FROM public.tasks_task
INNER JOIN public.schedules_frequency ON tasks_task.frequency_id = schedules_frequency.id
INNER JOIN public.timers_timer ON timers_timer.task_id = tasks_task.id;

一切都如你所愿.在Django项目中是否有不直接使用原始SQL的解决方案？