实体框架并发插入问题

Question

We are working on a MVC application. In this application we have a payment module. Once user starting a recurring subscription, application will get two responses from paypal for payment complete, with the same TransactionId. One is through “Success Url” and other one is through IPN listener. We are using a “Transaction”table to keep paypal transaction details. Application will check whether the “TransactionId” exist in the database, while getting a response from Paypal. So net result is first response from paypal will insert to “Transaction” table.

Recently We are having issues related with Entity Frame work concurrency. If the two response parellay comes, both the two records are inserting to the transaction table with the same “trnasction id”, even if we have the code for check existence of transactionid . How do we prevent this duplicate insertion? Both insertion is happening from different CONTEXT.

       var ipnDetail = unitOfWork.TransactionDetailRepository.GetTransaction(transactionNumber);
            if (ipnDetail == null)
            {
}

We are using same code for both insertion. Only difference is we are calling from different EF Context.

You can also note the first inserted entry having greater time than second inserted record. Actually we are setting the date from code. How do we solve this concurrency issue?

We tried to use a “ObjectContext.Refresh” for a solution. But it does not help us.

((IObjectContextAdapter)context).ObjectContext.Refresh(System.Data.Objects.RefreshMode.StoreWins, ((IObjectContextAdapter)context).ObjectContext.ObjectStateManager.GetObjectStateEntries(EntityState.Added));

Any help would be appreciable. Please note that application is in production environment.

Best Regards,

Ranish

Answer 1

If you have SQL Server 2014 or greater, the merge command is exactly what you need. It allows you to put the if condition at the right place in the operation.

The example below inserts your new transactionId if it does not exist in the database. Most alternatives involve a query followed by an insert, leaving a window in which another connection can sneak in an insert before yours completes.

You can find resources on the internet about calling a stored procedure from entity framework.

CREATE proc [dbo].[usp_InsertNewTransactionId](@transactionDate datetime2, @transactionId varchar(255))
as
begin
   ;with data as (select @transactionDate as transactionDate, @transactionId as transactionId)
   merge transactions t
   using data s
      on s.transactionId = t.transactionId
    when not matched by target
    then insert ([date],transactionId) values (s.transactionDate, s.transactionId);

end

Answer 2

Wrap the entire checking and inserting logic inside TransactionScope.

using (var scope = new TransactionScope(TransactionScopeOption.RequiresNew))
{
    // read & write logic here     

    scope.Complete();        
}

RequiresNew will cause a new transaction to be used and it should be blocked on the db level so your another request should be waiting until the first has completed the transaction either by adding the Id or not.