如何在Django/Python中获取倒数第二个最新的时间戳记录？

Question

我有一个模型的表单，它记录了进入/离开的时间。我正在尝试添加约束以使数据更准确。当前，当有人“进入”时，它会创建一个记录，将时间保存在“time\u in”DateTimeField中，然后重定向。如果此人再次尝试输入，它将创建一个带有新时间戳的新记录

我现在想补充的是，如果这个人以前有一个条目没有退出时间戳（time\u out），那么这个记录（这将是最后一个条目的第二个），将通过更新time\u exceptions字段到'N'来标记

当前，它将所有字段更改为“N”，而不管是否有出口，如下所示

注意我减少了表单\u valid中的代码量，因此不存在leave area部分。它只是基于其他字段的大量筛选，似乎不太相关

视图.py

class EnterExitArea(CreateView):
    model = EmployeeWorkAreaLog
    template_name = "operations/enter_exit_area.html"
    form_class = WarehouseForm

    def form_valid(self, form):
        emp_num = form.cleaned_data['employee_number']
        area = form.cleaned_data['work_area']
        station = form.cleaned_data['station_number']

        if 'enter_area' in self.request.POST:
            form.save()
            EmployeeWorkAreaLog.objects.filter((Q(employee_number=emp_num) & Q(work_area=area) & Q(time_out__isnull=True) & Q(time_in__isnull=True)) & (Q(station_number=station) | Q(station_number__isnull=True))).update(time_in=datetime.now())

            if EmployeeWorkAreaLog.objects.filter(Q(employee_number=emp_num)).count() > 1:
                EmployeeWorkAreaLog.objects.filter((Q(employee_number=emp_num) & Q(work_area=area) & Q(time_out__isnull=True)) & (Q(station_number=station) | Q(station_number__isnull=True))).update(time_exceptions='N')

            return HttpResponseRedirect(self.request.path_info)

我尝试了以下操作，但是得到了一个expected string or bytes-like object，虽然它在崩溃之前仍然创建了一个新记录，但它不会将第二个到最近一个的time\u异常更新为N

        if 'enter_area' in self.request.POST:
            form.save()
            EmployeeWorkAreaLog.objects.filter((Q(employee_number=emp_num) & Q(work_area=area) & Q(time_out__isnull=True) & Q(time_in__isnull=True)) & (Q(station_number=station) | Q(station_number__isnull=True))).update(time_in=datetime.now())

            if EmployeeWorkAreaLog.objects.filter(Q(employee_number=emp_num) & Q(time_out__isnull=True) & Q(time_exceptions="")).count() > 1:
                recent = EmployeeWorkAreaLog.objects.filter(employee_number=emp_num, work_area=area, station_number=station, time_out__isnull=True).order_by('-time_in')[1]

                EmployeeWorkAreaLog.objects.filter((Q(employee_number=emp_num) & Q(work_area=area) & Q(time_in=recent) & Q(time_out__isnull=True)) & (Q(station_number=station) | Q(station_number__isnull=True))).update(time_exceptions='N')

            return HttpResponseRedirect(self.request.path_info)

型号.py

class EmployeeWorkAreaLog(TimeStampedModel, SoftDeleteModel, models.Model):
    employee_number = models.ForeignKey(Salesman, on_delete=models.SET_NULL, help_text="Employee #", null=True, blank=False)
    work_area = models.ForeignKey(WorkArea, on_delete=models.SET_NULL, null=True, blank=False, help_text="Work Area", related_name="work_area")
    station_number = models.ForeignKey(StationNumber, on_delete=models.SET_NULL, 
    time_exceptions = models.CharField(max_length=2, blank=True)
    time_in = models.DateTimeField(help_text="Time in", null=True, blank=True)
    time_out = models.DateTimeField(blank=True, help_text="Time out", null=True)

    def __str__(self):
        return self.employee_number

回溯：

Internal Server Error: /operations/enter-exit-area/
Traceback (most recent call last):
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\core\handlers\exception.py", line 34, in inner
    response = get_response(request)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\core\handlers\base.py", line 126, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\core\handlers\base.py", line 124, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\views\generic\base.py", line 68, in view
    return self.dispatch(request, *args, **kwargs)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\views\generic\base.py", line 88, in dispatch
    return handler(request, *args, **kwargs)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\views\generic\edit.py", line 172, in post
    return super().post(request, *args, **kwargs)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\views\generic\edit.py", line 142, in post
    return self.form_valid(form)
  File "C:\Users\mkusneco\apps.rsrgroup.com\apps\operations\views.py", line 45, in form_valid
    Q(station_number=station) | Q(station_number__isnull=True))).update(time_exceptions='N')
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\db\models\manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\db\models\query.py", line 844, in filter
    return self._filter_or_exclude(False, *args, **kwargs)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\db\models\query.py", line 862, in _filter_or_exclude
    clone.query.add_q(Q(*args, **kwargs))
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\db\models\sql\query.py", line 1263, in add_q
    clause, _ = self._add_q(q_object, self.used_aliases)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\db\models\sql\query.py", line 1281, in _add_q
    current_negated, allow_joins, split_subq)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\db\models\sql\query.py", line 1287, in _add_q
    split_subq=split_subq,
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\db\models\sql\query.py", line 1225, in build_filter
    condition = self.build_lookup(lookups, col, value)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\db\models\sql\query.py", line 1096, in build_lookup
    lookup = lookup_class(lhs, rhs)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\db\models\lookups.py", line 20, in __init__
    self.rhs = self.get_prep_lookup()
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\db\models\lookups.py", line 70, in get_prep_lookup
    return self.lhs.output_field.get_prep_value(self.rhs)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\db\models\fields\__init__.py", line 1408, in get_prep_value
    value = super().get_prep_value(value)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\db\models\fields\__init__.py", line 1268, in get_prep_value
    return self.to_python(value)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\db\models\fields\__init__.py", line 1369, in to_python
    parsed = parse_datetime(value)
  File "C:\Users\mkusneco\appsve\lib\site-packages\django\utils\dateparse.py", line 106, in parse_datetime
    match = datetime_re.match(value)
TypeError: expected string or bytes-like object

Answer 1

将EmployeeWorkAreaLog实例赋给recent，但是在条件中使用它作为Q(time_in=recent)，这显然是错误的，因为条件需要包含简单的值/datetime/string，而不是对象

所以你可以通过使用Q(time_in=recent.time_in)来修复它，但是如果用户有一些重复的条目，那就不是很健壮了。使用实例的pk会更好，因此您应该使用time_in条件而不是Q(pk=recent.pk)。但这仍然不是最好的解决方案-如果有多个这样的条目呢？为什么只更新第二个而不更新第三个，等等

因此，我认为不应该选择第二个条目（使用[1]），而应该选择第一个条目，并从更新查询集中排除这个条目，例如：

first = EmployeeWorkAreaLog.objects.filter(employee_number=emp_num, work_area=area, station_number=station, time_out__isnull=True).order_by('-time_in').first()
EmployeeWorkAreaLog.objects.filter((Q(employee_number=emp_num) & Q(work_area=area) & Q(time_out__isnull=True)) & (Q(station_number=station) | Q(station_number__isnull=True))).exclude(pk=first.pk).update(time_exceptions='N')