(二十八)加锁

from rest_framework import exceptions
from django.db import transaction

　　def perform_create(self, serializer):
        with transaction.atomic():
            price = self.request.data.get(‘price‘)
            item_id = self.request.data.get(‘item‘)
            result = models.BidRecord.objects.filter(item_id=item_id).aggregate(max_price=Max(‘price‘)).select_for_update()
            max_price = result[‘max_price‘]
            if price > max_price:
                serializer.save(user=self.request.user)
            raise exceptions.ValidationError(‘已经被出价了，再涨涨.‘)