实体框架异常：SqlConnection 不支持并行事务

Question

我们有一个处理 XML 文件的应用程序。该应用程序使用 EF 6 将数据保存到 DB。应用程序使用 ThreadPool.QueueUserWorkItem 方法处理并发线程中的文件。该应用程序运行良好 1,5 年。 现在我们开始得到如下的 EF 异常：

大多数时候没有这样的错误，但是一天会出现几次。我们没有成功找出导致 EF 引发此错误的原因或条件。

有什么建议吗？

 An error occurred while starting a transaction on the provider connection. See the inner exception for details.
   at System.Data.Entity.Core.EntityClient.EntityConnection.BeginDbTransaction(IsolationLevel isolationLevel)
   at System.Data.Entity.Core.EntityClient.EntityConnection.BeginTransaction()
   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
   at System.Data.Entity.Core.Objects.ObjectContext.SaveChangesToStore(SaveOptions options, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction)
   at System.Data.Entity.Infrastructure.DbExecutionStrategy.Execute[TResult](Func`1 operation)
   at System.Data.Entity.Core.Objects.ObjectContext.SaveChangesInternal(SaveOptions options, Boolean executeInExistingTransaction)
   at System.Data.Entity.Internal.InternalContext.SaveChanges()
   at Albatross.Core.Utilities.BasicDataRepository`2.Update(T entity) in c:\DevTFS\AlbatrossEmployers\AlbatrossEmployers_DevTiyuvHeshb\Albatross.Core\Utilities\BasicDataRepository.cs:line 177
****** Inner Exception - START ******
SqlConnection does not support parallel transactions.
   at System.Data.SqlClient.SqlInternalConnection.BeginSqlTransaction(IsolationLevel iso, String transactionName, Boolean shouldReconnect)
   at System.Data.SqlClient.SqlConnection.BeginTransaction(IsolationLevel iso, String transactionName)
   at System.Data.SqlClient.SqlConnection.BeginDbTransaction(IsolationLevel isolationLevel)
   at System.Data.Entity.Infrastructure.Interception.InternalDispatcher`1.Dispatch[TTarget,TInterceptionContext,TResult](TTarget target, Func`3 operation, TInterceptionContext interceptionContext, Action`3 executing, Action`3 executed)
   at System.Data.Entity.Infrastructure.Interception.DbConnectionDispatcher.BeginTransaction(DbConnection connection, BeginTransactionInterceptionContext interceptionContext)
   at System.Data.Entity.Infrastructure.DbExecutionStrategy.Execute[TResult](Func`1 operation)
   at System.Data.Entity.Core.EntityClient.EntityConnection.BeginDbTransaction(IsolationLevel isolationLevel)
****** Inner Exception - END ******
~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Error - END ~~~~~~~~~~~~~~~~~~~~~~~~~~


The code is pretty simple:

     public virtual T Add(T entity)
        {
            try
            {
                using (U entityContext = new U())
                {
                    T addedEntity = Add(entity, entityContext);
                    entityContext.SaveChanges();
                    return addedEntity;
                }
            }
            catch (DbEntityValidationException e)
            {
                var msg = FormatDbValidationErrors(e);
                throw new Exception(msg);
            }
            catch (Exception ex)
            {
                AmanLog.Logger.Error(ex);
                throw;
            }
        }


 public virtual T Update(T entity)
        {
            try
            {
                using (U entityContext = new U())
                {
                    T existingEntity = Update(entity, entityContext);
                    entityContext.SaveChanges();
                    return existingEntity;
                }
            }
            catch (DbEntityValidationException e)
            {
                var msg = FormatDbValidationErrors(e);
                throw new Exception(msg);
            }
            catch (Exception ex)
            {
                AmanLog.Logger.Error(ex);
                throw;
            }
        }

Answer 1

应用程序使用 ThreadPool.QueueUserWorkItem 方法处理并发线程中的文件。

您不能从两个线程同时使用相同的连接，否则：会发生这种情况。要么：

• 通过单个连接/数据库上下文进行同步，这样就不能一次使用两次（lock 是实现此目的的简单方法）
• 使用每个工作项的连接/数据库上下文，以便不共享任何内容