MultipleObjectMixin
这也是一个有趣的东西。
class MultipleObjectMixin(ContextMixin):
"""A mixin for views manipulating multiple objects."""
allow_empty = True
queryset = None
model = None
paginate_by = None
paginate_orphans = 0
context_object_name = None
paginator_class = Paginator
page_kwarg = 'page'
ordering = None
def get_queryset(self):
"""
Return the list of items for this view.
The return value must be an iterable and may be an instance of
`QuerySet` in which case `QuerySet` specific behavior will be enabled.
"""
if self.queryset is not None:
queryset = self.queryset
if isinstance(queryset, QuerySet):
queryset = queryset.all()
elif self.model is not None:
queryset = self.model._default_manager.all()
else:
raise ImproperlyConfigured(
"%(cls)s is missing a QuerySet. Define "
"%(cls)s.model, %(cls)s.queryset, or override "
"%(cls)s.get_queryset()." % {
'cls': self.__class__.__name__
}
)
ordering = self.get_ordering()
if ordering:
if isinstance(ordering, str):
ordering = (ordering,)
queryset = queryset.order_by(*ordering)
return queryset
def get_ordering(self):
"""Return the field or fields to use for ordering the queryset."""
return self.ordering
def paginate_queryset(self, queryset, page_size):
"""Paginate the queryset, if needed."""
paginator = self.get_paginator(
queryset, page_size, orphans=self.get_paginate_orphans(),
allow_empty_first_page=self.get_allow_empty())
page_kwarg = self.page_kwarg
page = self.kwargs.get(page_kwarg) or self.request.GET.get(page_kwarg) or 1
try:
page_number = int(page)
except ValueError:
if page == 'last':
page_number = paginator.num_pages
else:
raise Http404(_("Page is not 'last', nor can it be converted to an int."))
try:
page = paginator.page(page_number)
return (paginator, page, page.object_list, page.has_other_pages())
except InvalidPage as e:
raise Http404(_('Invalid page (%(page_number)s): %(message)s') % {
'page_number': page_number,
'message': str(e)
})
def get_paginate_by(self, queryset):
"""
Get the number of items to paginate by, or ``None`` for no pagination.
"""
return self.paginate_by
def get_paginator(self, queryset, per_page, orphans=0,
allow_empty_first_page=True, **kwargs):
"""Return an instance of the paginator for this view."""
return self.paginator_class(
queryset, per_page, orphans=orphans,
allow_empty_first_page=allow_empty_first_page, **kwargs)
def get_paginate_orphans(self):
"""
Return the maximum number of orphans extend the last page by when
paginating.
"""
return self.paginate_orphans
def get_allow_empty(self):
"""
Return ``True`` if the view should display empty lists and ``False``
if a 404 should be raised instead.
"""
return self.allow_empty
def get_context_object_name(self, object_list):
"""Get the name of the item to be used in the context."""
if self.context_object_name:
return self.context_object_name
elif hasattr(object_list, 'model'):
return '%s_list' % object_list.model._meta.model_name
else:
return None
def get_context_data(self, *, object_list=None, **kwargs):
"""Get the context for this view."""
queryset = object_list if object_list is not None else self.object_list
page_size = self.get_paginate_by(queryset)
context_object_name = self.get_context_object_name(queryset)
if page_size:
paginator, page, queryset, is_paginated = self.paginate_queryset(queryset, page_size)
context = {
'paginator': paginator,
'page_obj': page,
'is_paginated': is_paginated,
'object_list': queryset
}
else:
context = {
'paginator': None,
'page_obj': None,
'is_paginated': False,
'object_list': queryset
}
if context_object_name is not None:
context[context_object_name] = queryset
context.update(kwargs)
return super().get_context_data(**context)
class BaseListView(MultipleObjectMixin, View):
"""A base view for displaying a list of objects."""
def get(self, request, *args, **kwargs):
self.object_list = self.get_queryset()
allow_empty = self.get_allow_empty()
if not allow_empty:
# When pagination is enabled and object_list is a queryset,
# it's better to do a cheap query than to load the unpaginated
# queryset in memory.
if self.get_paginate_by(self.object_list) is not None and hasattr(self.object_list, 'exists'):
is_empty = not self.object_list.exists()
else:
is_empty = not self.object_list
if is_empty:
raise Http404(_("Empty list and '%(class_name)s.allow_empty' is False.") % {
'class_name': self.__class__.__name__,
})
context = self.get_context_data()
return self.render_to_response(context)
class MultipleObjectTemplateResponseMixin(TemplateResponseMixin):
"""Mixin for responding with a template and list of objects."""
template_name_suffix = '_list'
def get_template_names(self):
"""
Return a list of template names to be used for the request. Must return
a list. May not be called if render_to_response is overridden.
"""
try:
names = super().get_template_names()
except ImproperlyConfigured:
# If template_name isn't specified, it's not a problem --
# we just start with an empty list.
names = []
# If the list is a queryset, we'll invent a template name based on the
# app and model name. This name gets put at the end of the template
# name list so that user-supplied names override the automatically-
# generated ones.
if hasattr(self.object_list, 'model'):
opts = self.object_list.model._meta
names.append("%s/%s%s.html" % (opts.app_label, opts.model_name, self.template_name_suffix))
elif not names:
raise ImproperlyConfigured(
"%(cls)s requires either a 'template_name' attribute "
"or a get_queryset() method that returns a QuerySet." % {
'cls': self.__class__.__name__,
}
)
return names
class ListView(MultipleObjectTemplateResponseMixin, BaseListView):
"""
Render some list of objects, set by `self.model` or `self.queryset`.
`self.queryset` can actually be any iterable of items, not just a queryset.
"""
