[英]django model select_related or prefetch_related child model
新手,我有两个型号,如下
class ReceipeMaster(models.Model):
receipe_type = models.CharField(max_length=50, choices=TYPE_OPTIONS, default=TYPE_OPTIONS[0])
item = models.ForeignKey(Item, on_delete=models.CASCADE, related_name='receipe')
units = models.IntegerField(default=1)
status = models.BooleanField(default=True)
class ReceipeDetail(models.Model):
master = models.ForeignKey(ReceipeMaster, on_delete=models.CASCADE, related_name='items')
item_type = models.ForeignKey(Item_type, null=True, on_delete=models.PROTECT)
item = models.ForeignKey(Item, on_delete=models.PROTECT)
quantity = models.IntegerField()
我有一个详细的视图DetailView
class ReceipeDetailView(PermissionRequiredMixin, DetailView):
permission_required = 'item_management.view_receipemaster'
model = ReceipeMaster
template_name = 'receipes/show.html'
context_object_name = 'receipe'
我想在ReceipeMaster
model 和ReceipeDetail
select_related
上prefetch_related
相关或选择相关。 只需在两个模型上预取即可。
问候
要自定义如何在通用视图中获取查询集,需要覆盖视图的get_queryset
方法。 此外,如果想在预取的 object 上使用select_related
,则应该使用Prefetch
objects [Django docs]并指定它们的queryset
。 由于这是一个DetailView
并因此处理一个 object 您将需要覆盖get_object
:
from django.db.models import Prefetch
from django.http import Http404
from django.utils.translation import gettext as _
class ReceipeDetailView(PermissionRequiredMixin, DetailView):
permission_required = 'item_management.view_receipemaster'
model = ReceipeMaster
template_name = 'receipes/show.html'
context_object_name = 'receipe'
def get_object(self, queryset=None):
# Use a custom queryset if provided; this is required for subclasses
# like DateDetailView
if queryset is None:
queryset = self.get_queryset()
# Next, try looking up by primary key.
pk = self.kwargs.get(self.pk_url_kwarg)
slug = self.kwargs.get(self.slug_url_kwarg)
if pk is not None:
queryset = queryset.filter(pk=pk)
# Next, try looking up by slug.
if slug is not None and (pk is None or self.query_pk_and_slug):
slug_field = self.get_slug_field()
queryset = queryset.filter(**{slug_field: slug})
# If none of those are defined, it's an error.
if pk is None and slug is None:
raise AttributeError(
"Generic detail view %s must be called with either an object "
"pk or a slug in the URLconf." % self.__class__.__name__
)
queryset = queryset.select_related('item').prefetch_related(
Prefetch(
'items',
queryset=ReceipeDetail.objects.select_related('item_type', 'item')
)
)
try:
# Get the single item from the filtered queryset
obj = queryset.get()
except queryset.model.DoesNotExist:
raise Http404(_("No %(verbose_name)s found matching the query") %
{'verbose_name': queryset.model._meta.verbose_name})
return obj
您可以完全覆盖get_queryset
方法,而无需调用super()
:
def get_queryset(self):
queryset = ReceipeMaster.objects.select_related('item').prefetch_related(
Prefetch(
'items',
queryset=ReceipeDetail.objects.select_related('item_type', 'item'),
)
)
return queryset
然后get_object
方法将过滤查询集以获取queryset
。 在这种情况下这不会成为问题,因为filter()
和select_related()
链接的顺序并不重要( docs )。
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