Django 过滤 timedelta 错误：TypeError: expected string or bytes-like object

Question

我有一个模型 Run，其中包含 start_time 和 end_time 时间戳，表示数据测量的开始和结束（我们称之为“跑”）。

class Run(models.Model):
    start_time = models.DateTimeField(db_index=True)
    end_time = models.DateTimeField()

最近，一位客户开始执行新类型的操作，其中一项要求他们知道运行的持续时间（很容易弄清楚），还需要根据该持续时间过滤表格。

过滤是我没有的部分。因此，尝试按持续时间（模型上没有的字段）进行过滤，我想出了以下查询：

from django.db.models import F

test_query = Run.objects.all().annotate(duration=F('end_time') - F('start_time'))

通过使用 annotate 和 F 操作，我可以在我的查询中添加一个新的临时字段，称为“duration”。新字段的类型为datetime.timedelta，因为它是对两个datetime 对象执行算术运算的结果。该部分按预期工作。

问题归结为尝试通过使用__gte 和__lte 查找来过滤新生成的注释：

from datetime import timedelta
from django.db.models import F

test_query = Run.objects.all().annotate(duration=F('end_time') - F('start_time')).filter(duration__gte=timedelta(seconds=50))

为简单起见，假设我只想获得 50 秒或更长时间的 Runs，例如。

到目前为止，我在 timedelta 方面的工作非常简单。 end_time - start_time = timedelta_datetime_span

除了django过滤器，它似乎不想把它作为参数，抛出以下错误：

Traceback (most recent call last):
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/core/handlers/base.py", line 115, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/core/handlers/base.py", line 113, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/lib/python3.5/contextlib.py", line 30, in inner
    return func(*args, **kwds)
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/contrib/auth/decorators.py", line 21, in _wrapped_view
    return view_func(request, *args, **kwargs)
  File "/home/foo/Projects/project_foo/project_foo/comp_foo/foo/views.py", line 2790, in RunsJson
    test = Run.objects.all().annotate(duration=F('end_time') - F('start_time')).filter(duration__gte=timedelta(seconds=50))
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/db/models/query.py", line 892, in filter
    return self._filter_or_exclude(False, *args, **kwargs)
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/db/models/query.py", line 910, in _filter_or_exclude
    clone.query.add_q(Q(*args, **kwargs))
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/db/models/sql/query.py", line 1290, in add_q
    clause, _ = self._add_q(q_object, self.used_aliases)
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/db/models/sql/query.py", line 1318, in _add_q
    split_subq=split_subq, simple_col=simple_col,
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/db/models/sql/query.py", line 1207, in build_filter
    condition = self.build_lookup(lookups, reffed_expression, value)
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/db/models/sql/query.py", line 1116, in build_lookup
    lookup = lookup_class(lhs, rhs)
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/db/models/lookups.py", line 20, in __init__
    self.rhs = self.get_prep_lookup()
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/db/models/lookups.py", line 70, in get_prep_lookup
    return self.lhs.output_field.get_prep_value(self.rhs)
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/db/models/fields/__init__.py", line 1410, in get_prep_value
    value = super().get_prep_value(value)
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/db/models/fields/__init__.py", line 1270, in get_prep_value
    return self.to_python(value)
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/db/models/fields/__init__.py", line 1371, in to_python
    parsed = parse_datetime(value)
  File "/home/foo/.virtualenvs/project_foo/lib/python3.5/site-packages/django/utils/dateparse.py", line 106, in parse_datetime
    match = datetime_re.match(value)
TypeError: expected string or bytes-like object

.annotate() 之后的 .filter() 串联应该适用于新的 duration 字段，因为（afaik）__gte 或 __lte 查找适用于 datetime.timedelta 对象。

我在这里过滤有什么问题？

Answer 1

在我的一项任务中，我遇到了与您类似的问题。我希望这对你有用。您应该像这样使用ExpressionWrapper 表达式：

from django.db.models import ExpressionWrapper, DurationField

Run.objects.all().annotate(duration=ExpressionWrapper(F('end_time') - F('start_time'), output_field=DurationField()))

使用此解决方案，您可以使用duration__gte 或duration__lte。