Python Django&；SQLite:DurationField算法

我有下面的型号

class MyModel(models.Model):
    start = models.TimeField()
    finish = models.TimeField()
    penalty = models.IntegerField(blank=True, default=0)  # penalty in minutes

以及以下管理中的queryset注释

def get_queryset(self, request):
    qs = super().get_queryset(request)
    qs = qs.annotate(
        total_time=ExpressionWrapper(
            F("finish") - F("start") + F("penalty") * 60,
            output_field=DurationField()
        )
    )
    return qs

当我检查

惩罚！=0

我得到类似于

datetime.timedelta（018001800）

（在这种情况下，惩罚是30分钟）。
但是，我希望使用类似于

datetime.timedelta（03600）

的timedelta。有人能解释一下吗

我也试过了

def get_queryset(self, request):
    qs = super().get_queryset(request)
    qs = qs.annotate(
        duration=ExpressionWrapper(
            F("finish") - F("start"),
            output_field=DurationField()
        )
    )
    qs = qs.annotate(
        total_time=ExpressionWrapper(
            F("duration") + F("route_shortening_penalty") * 60,
            output_field=DurationField()
        )
    )
    return qs

甚至

def get_queryset(self, request):
    qs = super().get_queryset(request)
    qs = qs.annotate(
        duration=ExpressionWrapper(
            F("finish") - F("start"),
            output_field=DurationField()
        ),
        penalty_duration=ExpressionWrapper(
            F("penalty") * 60,
            output_field=DurationField()
        )
    )
    qs = qs.annotate(
        total_time=ExpressionWrapper(
            F("duration") + F("penalty_duration"),
            output_field=DurationField()
        )
    )
    return qs

这两种情况都会导致

Traceback (most recent call last):
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/core/handlers/base.py", line 126, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/core/handlers/base.py", line 124, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/contrib/admin/options.py", line 604, in wrapper
    return self.admin_site.admin_view(view)(*args, **kwargs)
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/utils/decorators.py", line 142, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/views/decorators/cache.py", line 44, in _wrapped_view_func
    response = view_func(request, *args, **kwargs)
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/contrib/admin/sites.py", line 223, in inner
    return view(request, *args, **kwargs)
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/utils/decorators.py", line 45, in _wrapper
    return bound_method(*args, **kwargs)
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/utils/decorators.py", line 142, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/contrib/admin/options.py", line 1793, in changelist_view
    'selection_note': _('0 of %(cnt)s selected') % {'cnt': len(cl.result_list)},
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/db/models/query.py", line 250, in __len__
    self._fetch_all()
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/db/models/query.py", line 1186, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/db/models/query.py", line 63, in __iter__
    for row in compiler.results_iter(results):
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/db/models/sql/compiler.py", line 1009, in apply_converters
    value = converter(value, expression, connection)
  File "/home/dm/.virtualenvs/test/lib/python3.6/site-packages/django/db/backends/base/operations.py", line 573, in convert_durationfield_value
    return datetime.timedelta(0, 0, value)
TypeError: unsupported type for timedelta microseconds component: str

---

我正在使用

python3.6.7

，

Django==2.1.7

和

SQLite版本3022000

，如果你得到的是

datetime.timedelta（0，1800，1800）

而不是正确的

datetime.timedelta（0，3600）

，那么你显然就快到了

我假设1800秒是

F（“完成”）

和

F（“开始”）

之间的差，而1800微秒来自

F（“惩罚”）*60

用

60*1000*1000

而不是

60

相乘，将

惩罚

从分钟转换为微秒：

total_time=ExpressionWrapper(
    F("finish") - F("start") + F("penalty") * 60000000,
    output_field=DurationField()
)

---

如果惩罚是一个

DurationField

而不是一个

IntegerField

，这不是更有意义吗？@JohnGordon也尝试过了，请参见更新的问题。为什么不使用类属性而不是注释？@Pedro，因为无法对属性的变更列表视图进行排序。我想根据注释结果进行排序。我没有看到任何代码表明您尝试了不同的模型定义。我只看到了对

get\u queryset（）

的更改。好的，所以有效的方法是乘以

60000000

（1秒=1000000微秒）。接受，因为你给我指出了正确的方向，请相应地更新答案。谢谢。我应该先让我的孩子们做转化。