7,并发处理

概要：

       学习并发的处理，和事物处理。

内容：

       var query = from p inctx.Products where p.CategoryID == 1 select p;

        foreach(var p inquery)

           p.UnitsInStock = Convert.ToInt16(p.UnitsInStock- 1);

       ctx.SubmitChanges(); // 在这里设断点，可能出现并发

 

       去除更新检测：

       [Column(Storage="_UnitPrice",DbType="Money", UpdateCheck = UpdateCheck.Never)]

         这样如果发生并发，则默认以最后一次更新为准。

 

         处理并发：

                   var query = from p inctx.Products where p.CategoryID == 1 select p;

       foreach (var p in query)

           p.UnitsInStock = Convert.ToInt16(p.UnitsInStock- 1);

       try

       {

ctx.SubmitChanges(ConflictMode.FailOnFirstConflict);//遇到并发，不继续

           ctx.SubmitChanges(ConflictMode.ContinueOnConflict);//遇到并发，还是继续

       }

       catch (ChangeConflictException)

       {

           foreach (ObjectChangeConflictcc in ctx.ChangeConflicts)//获取并发对象

           {

               Product p = (Product)cc.Object;

               Response.Write(p.ProductID + "<br/>");

                   cc.Resolve(RefreshMode.KeepCurrentValues);// 放弃原先更新，所有更新以当前更新 为准

       cc.Resolve(RefreshMode.KeepChanges); // 原先更新有效，冲突字段以当前更新 为准

 

               cc.Resolve(RefreshMode.OverwriteCurrentValues); // 放弃当前更新，所有更新以原先更新为准

           }

       }

       ctx.SubmitChanges();

 

事务处理：

       LinQto sql在提交更新的时候默认会创建事务，一部分修改发生错误的话其它修改也不会生效：

               ctx.Customers.Add(newCustomer { CustomerID = "abcdf", CompanyName = "zhuye" });

                           ctx.Customers.Add(newCustomer { CustomerID = "abcde", CompanyName = "zhuye" });

                           ctx.SubmitChanges();

其他处理办法：

              if(ctx.Connection != null) ctx.Connection.Open();

        DbTransactiontran = ctx.Connection.BeginTransaction();

        ctx.Transaction = tran;

        try

        {

           CreateCustomer(new Customer{ CustomerID = "abcdf",CompanyName = "zhuye" });

           CreateCustomer(new Customer{ CustomerID = "abcde",CompanyName = "zhuye" });

           tran.Commit();

        }

        catch

        {

           tran.Rollback();

        }

 

    private void CreateCustomer(Customerc)

    {

        ctx.Customers.Add(c);

        ctx.SubmitChanges();

    }

第二种：

              using (TransactionScope scope = new TransactionScope())

        {

           CreateCustomer(new Customer{ CustomerID = "abcdf",CompanyName = "zhuye" });

           CreateCustomer(new Customer{ CustomerID = "abcde",CompanyName = "zhuye" });

           scope.Complete();

       }