我有一个半大型软件。有一次，我将table2包含在该项目中并开始使用它。我在filter.py文件中包含了一些基本的模型过滤。现在，如果我删除我的数据库并尝试运行新的迁移，我会收到错误，该表无法使用。我建立了一个尝试捕获并且它正在工作，因为它不会在迁移之前运行代码剪切。
class PracticephaseProjectFilter(django_filters.FilterSet):
omni = django_filters.CharFilter(method=omni_search, label="Suche")
practice_phase = django_filters.ModelChoiceFilter(queryset=PracticePhase.objects.filter(pk__in=get_pp_for_specialpermit()))
class Meta:
model = PracticePhaseProject
fields = ['practice_phase']
def __init__(self, *args, **kwargs):
super(PracticephaseProjectFilter, self).__init__(*args, **kwargs)
def get_pp_for_specialpermit():
pp = []
today = date.today()
# check if SS or WS required
if 4 <= today.month <= 9:
# current SS, project will be sought for WS this year
pp_str = [str(today.year)[-2:] + "s", str(today.year - 1)[-2:] + "w"]
# we are in WS, check correct year for SS
elif today.month > 9:
pp_str = [str(today.year)[-2:] + "w", str(today.year)[-2:] + "s"]
# we are allready in the year of next SS
else:
pp_str = [str(today.year - 1)[-2:] + "s", str(today.year - 1)[-2:] + "w"]
try:
for _pp in PracticePhase.objects.filter(semester__name__in=pp_str):
pp.append(_pp.pk)
except:
pass
return pp
现在，如果我删除for循环的try catch，我就无法运行迁移，因为我遇到数据库错误，没有table practicephase。但是在迁移之前永远不应该调用该文件。
分析解答
系统检查框架在makemigrations和migrate命令运行之前运行。
URL检查会导致您的urls.py被导入，从而加载包含PracticephaseProjectFilter的module。
您不应该在filterset定义中调用get_pp_for_specialpermit - 这意味着查询将在服务器启动时运行一次。这意味着在Django服务器准备就绪之前，您有一个不必要的查询，结果可能会在以后失效。
您可以通过将查询集移动到__init__方法来阻止查询运行：
class PracticephaseProjectFilter(django_filters.FilterSet):
omni = django_filters.CharFilter(method=omni_search, label="Suche")
practice_phase = django_filters.ModelChoiceFilter(queryset=PracticePhase.objects.none())
class Meta:
model = PracticePhaseProject
fields = ['practice_phase']
def __init__(self, *args, **kwargs):
super(PracticephaseProjectFilter, self).__init__(*args, **kwargs)
self.filters['practice_phase'].queryset = PracticePhase.objects.filter(pk__in=get_pp_for_specialpermit())