django-rest-framework 加快序列化程序查询
示例
假设我们有Travel很多相关领域的模型：
class Travel(models.Model):
tags = models.ManyToManyField(
Tag,
related_name='travels', )
route_places = models.ManyToManyField(
RoutePlace,
related_name='travels', )
coordinate = models.ForeignKey(
Coordinate,
related_name='travels', )
date_start = models.DateField()我们想/travels通过ViewViewSet构建CRUD。
这是简单的视图集：
class TravelViewset(viewsets.ModelViewSet):
queryset = Travel.objects.all()
serializer_class = TravelSerializer该ViewSet的问题在于我们的Travel模型中有许多相关字段，因此Django将为每个Travel实例命中db。我们可以称之为select_related并直接prefetch_relatedqueryset属性，但如果我们想单独为串行什么list，retrieve，create...视图集中行动。
因此，我们可以将此逻辑放入一个mixin并从中继承：
class QuerySerializerMixin(object):
PREFETCH_FIELDS = [] # Here is for M2M fields
RELATED_FIELDS = [] # Here is for ForeignKeys
@classmethod
def get_related_queries(cls, queryset):
# This method we will use in our ViewSet
# for modify queryset, based on RELATED_FIELDS and PREFETCH_FIELDS
if cls.RELATED_FIELDS:
queryset = queryset.select_related(*cls.RELATED_FIELDS)
if cls.PREFETCH_FIELDS:
queryset = queryset.prefetch_related(*cls.PREFETCH_FIELDS)
return queryset
class TravelListSerializer(QuerySerializerMixin, serializers.ModelSerializer):
PREFETCH_FIELDS = ['tags'']
RELATED_FIELDS = ['coordinate']
# I omit fields and Meta declare for this example
class TravelRetrieveSerializer(QuerySerializerMixin, serializers.ModelSerializer):
PREFETCH_FIELDS = ['tags', 'route_places']现在ViewSet用新的序列化器重写我们的
class TravelViewset(viewsets.ModelViewSet):
queryset = Travel.objects.all()
def get_serializer_class():
ifself.action== 'retrieve':
return TravelRetrieveSerializer
elifself.action== 'list':
return TravelListSerializer
else:
return SomeDefaultSerializer
def get_queryset(self):
# This method return serializer class
# which we pass in class method of serializer class
# which is also return by get_serializer()
q = super(TravelViewset, self).get_queryset()
serializer = self.get_serializer()
return serializer.get_related_queries(q)
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