[英]django rest framework: prefetch an initial data in serializer
我知道django具有select_related和prefetch_related,可以在从数据库查询项目以提高其性能时使用,并且可以与django rest框架的嵌套序列化程序一起使用。
但是,当我想使用序列化程序来创建模型时,问题就来了:
class CompanySerializer(serializer.serializers):
employee_set = serializers.JSONField()
class Meta:
model = Company
fields = ('id', 'employee_set')
def create(self, validated_data):
employee_set = validated_data.pop('employee_set')
for employee in employee_set:
serializer = EmployeeSerializer(data=employee)
serializer.is_valid(raise_exception=True)
serializer.save()
class EmployeeSerializer(serializer.serializers):
card = serializers.PrimaryKeyRelatedField(queryset=Card.objects.all())
class Meta:
model = Employee
fields = ('id', 'name', 'card')
def validate(self, obj):
if card.employee_set.all().count() > 3:
raise serializers.ValidationError({'_error': 'invalid})
return data
例如,我想创建一个拥有多个员工的公司,例如:
request.POST:
{
employee_set: [
{ name: 'tim', card: 1 },
{ name: 'bob', card: 1 },
{ name: 'jimmy', card: 2},
]
}
然后我可以使用CompanySerializer(request.POST),对吗?
但是,当我保存此序列化程序时,EmployeeSerializer将遍历每个员工并查询employee.card_set,这将导致大量的SQL查询。 有没有办法像prefetch_related这样呢?
谢谢
您可以通过context
将其他信息发送到序列化器context
# use select_related or prefetech_related to get this value
card_counters = {'card_id1': 1, 'card_id2': 3, ...}
for employee in employee_set:
serializer = EmployeeSerializer(
data=employee,
context={'card_counter': card_counters.get(employee['card_id'], 0)}
)
...
然后在进行验证时使用它:
def validate(self, obj):
if self.context['card_counter'] > 3:
raise serializers.ValidationError({'_error': 'invalid})
return data
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