数据库操作的事务与锁

django

后端逻辑

def transaction_add(request, pk):
    res_code = ResCode()
    if request.method == 'POST':
        form = TransactionForm(data=request.POST)
        if not form.is_valid():
            res_code.detail = form.errors
            return JsonResponse(res_code.dict)
        amount = form.cleaned_data.get('amount')
        status = form.cleaned_data.get('status')
        # 防止页面错误
        try:
            # 原子性操作，事务绑定，失败一起回滚
            from django.db import transaction
            with transaction.atomic():
		#select_for_update()加锁，只能单个事务执行
                trader = models.User.objects.filter(pk=pk).select_for_update().first()
                form.instance.trader = trader
                form.instance.operator_id = request.user_info.uid
                if status == 1:
                    trader.balance += amount
                elif status == 2:
                    if trader.balance < amount:
                        # 自定义显示错误，amount为字段名
                        res_code.detail = {
                            'amount': [f'余额不足，当前余额为{trader.balance}']
                        }
                        return JsonResponse(res_code.dict)
                    trader.balance -= amount
                trader.save()
                form.save()
        except Exception as e:
            res_code.detail = {
                'amount': ['操作失败', e]
            }
            return JsonResponse(res_code.dict)
        res_code.success = True
        res_code.detail = ''
        return JsonResponse(res_code.dict)

drf

局部事务（*）

基于上下文管理，如果出现异常则自动回滚；无异常则自动提交。

from rest_framework.views import APIView
from rest_framework.response import Response
from django.db import transaction
from api import models


class Demo1View(APIView):
    def get(self, request, *args, **kwargs):
        try:
            with transaction.atomic():
                models.UserInfo.objects.create(name='v1', age=1)
                models.Order.objects.create(name='v1', age=1)
        except Exception as e:
            print("异常，自动回滚")

        return Response("...")

事务提交的回调函数（本质上就是事务完成后，自动执行一个函数）

from rest_framework.views import APIView
from rest_framework.response import Response
from django.db import transaction
from api import models
from functools import partial


def db_success_callback(*args, **kwargs):
    print(args, **kwargs)

class Demo1View(APIView):
    def get(self, request, *args, **kwargs):
        try:
            with transaction.atomic():
                # 回调函数，事务正常提交自动执行
                transaction.on_commit(db_success_callback)
                transaction.on_commit( partial(db_success_callback, 11, 22, 33) )

                models.UserInfo.objects.create(name='v1', age=1)
                models.Order.objects.create(title='v1', count=1)
        except Exception as e:
            print("异常，自动回滚") # on_commit回调函数内部异常时不会回滚

        return Response("...")

回滚到 指定事务点

from rest_framework.views import APIView
from rest_framework.response import Response
from django.db import transaction
from api import models


class Demo1View(APIView):
    def get(self, request, *args, **kwargs):
        try:
            with transaction.atomic():
                # 回调函数，事务正常提交自动执行
                n1 = transaction.savepoint()
                models.UserInfo.objects.create(name='v1', age=1)
                n2 = transaction.savepoint()
                models.UserInfo.objects.create(name='v2', age=1)

                # 必须在事务里面，回顾到指定 事务点，后续东西不提交
                transaction.savepoint_rollback(n2)
        except Exception as e:
            print("异常，自动回滚", e)  # on_commit回调函数内部异常时不会回滚

        return Response("...")

视图事务

针对整个视图进行开启事务：

• 视图内，有数据库操作异常，自动回滚
• 视图内，有其他异常，不会回滚。

from rest_framework.views import APIView
from rest_framework.response import Response
from django.db import transaction, IntegrityError
from api import models


class Demo1View(APIView):

    @transaction.atomic
    def get(self, request, *args, **kwargs):
        try:
            models.UserInfo.objects.create(name='v100', age=1)
            models.UserInfo.objects.create(name="v200", age="xxx")  # 有异常，回滚，即：v100不会保存
            int("asdf")   # 有异常，不会滚，即：两条数据正常保存到数据库
        except Exception as e:
            pass
        return Response("...")

定义事务点，自定义回滚位置

from rest_framework.views import APIView
from rest_framework.response import Response
from django.db import transaction, IntegrityError
from api import models


class Demo1View(APIView):

    @transaction.atomic
    def get(self, request, *args, **kwargs):
        try:
            models.UserInfo.objects.create(name='v10', age=1)
            n1 = transaction.savepoint()
            models.UserInfo.objects.create(name="v11", age=1)
            n2 = transaction.savepoint()
            models.UserInfo.objects.create(name='v12', age=1)
            n3 = transaction.savepoint()
            models.UserInfo.objects.create(name='v13', age=1)
            # 后续读取到某些值后，发现 v12不应该创建，那么就可以主动回滚
            transaction.savepoint_rollback(n1)
        except Exception as e:
            print("有异常", e)
        return Response("...")

有的cvb需要把装饰器放在dispatch上才生效

from django.utils.decorators import method_decorator
from django.db import transaction

@method_decorator(transaction.atomic, name='dispatch')
class LoginView(APIView):
	pass

全局事务

效率低：项目中一般不会使用。
如果想要开启全局事务，需要在连接数据库时多设置一个参数

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'dbhot4',
        'USER': 'root',
        'PASSWORD': 'root123',
        'HOST': '127.0.0.1',
        'PORT': '3306',
        'ATOMIC_REQUESTS': True
    }
}

只要视图函数执行异常，无论是什么原因触发，均自动回滚。

class Demo1View(APIView):
    def get(self, request, *args, **kwargs):
        models.UserInfo.objects.create(name='v1', age=1)
        models.UserInfo.objects.create(xxxxxxx='v2', age=1) # 错误
        return Response("...")

class Demo1View(APIView):
    def get(self, request, *args, **kwargs):
        models.UserInfo.objects.create(name='v1', age=1)
        models.UserInfo.objects.create(name='v2', age=1)
        int("asdf")  # 错误
        return Response("...")

如果视图函数执行不报错（try处理异常，也叫不报错），则不会回滚

class Demo1View(APIView):
    def get(self, request, *args, **kwargs):
        try:
            models.UserInfo.objects.create(name='v1', age=1)
            models.UserInfo.objects.create(xxxxxxx='v2', age=1)
            int("xxx")
        except Exception as e:
            pass
        return Response("...")
# 视图函数执行没有报错，不会滚回。

如果开启了全局事务，想要免除某个指定的函数不需要开启事务，则可以使用

from rest_framework.views import APIView
from rest_framework.response import Response
from django.db import transaction, IntegrityError
from api import models
from django.utils.decorators import method_decorator


@method_decorator(transaction.non_atomic_requests, name='dispatch')
class Demo1View(APIView):

    def get(self, request, *args, **kwargs):
        models.UserInfo.objects.create(name='v100', age=1)
        models.UserInfo.objects.create(name="v200", age="xxx") # 报错
        return Response("...")