我有一个半大型软件。有一次我将 tables2 包含到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，我会收到错误消息，即该表不可用。我构建了一个 try catch around 并且它正在工作，因为它不运行迁移之前截断的代码。
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 循环周围的 try catch，我将无法运行迁移，因为我遇到数据库错误，即没有表练习阶段。但在迁移之前不应调用该文件。
请您参考如下方法:
system checks framework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，它会加载包含 PracticephaseProjectFilter 的模块。
您不应该在过滤器集定义中调用 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 服务器准备好之前您有一个不必要的查询，并且结果稍后可能会过时。
您可以通过将查询集移动到 __init__ 方法中来阻止查询运行:
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())
