entity-framework - 调用 saveChanges 时出错

Question

添加新记录时出现以下错误

System.Data.Entity.Infrastructure.DbUpdateException was caught
HResult=-2146233087
Message=An error occurred while updating the entries. See the inner exception for details.
Source=EntityFramework
StackTrace:
   at System.Data.Entity.Internal.InternalContext.SaveChanges()
   at System.Data.Entity.Internal.LazyInternalContext.SaveChanges()
   at System.Data.Entity.DbContext.SaveChanges()
   at Navigation.RepositoryBase`2.Add(T entity) in c:\Users\afahmy\Documents\Visual Studio 2012\Projects\Navigation\REpositoryBase.cs:line 174
InnerException: System.Data.UpdateException
   HResult=-2146233087
   Message=An error occurred while updating the entries. See the inner exception for details.
   Source=System.Data.Entity
   StackTrace:
        at System.Data.Mapping.Update.Internal.UpdateTranslator.Update(IEntityStateManager stateManager, IEntityAdapter adapter)
        at System.Data.EntityClient.EntityAdapter.Update(IEntityStateManager entityCache)
        at System.Data.Objects.ObjectContext.SaveChanges(SaveOptions options)
        at System.Data.Entity.Internal.InternalContext.SaveChanges()
   InnerException: System.Data.SqlClient.SqlException
        HResult=-2146232060
        Message=Violation of PRIMARY KEY constraint 'PK_dbo.Priorities'. Cannot insert duplicate key in object 'dbo.Priorities'. The duplicate key value is (55c9b08f-1133-4246-9d0b-4f3e5192ffa5).

The statement has been terminated.
        Source=.Net SqlClient Data Provider
        ErrorCode=-2146232060
        Class=14
        LineNumber=1
        Number=2627
        Procedure=""
        Server=dbsrv
        State=1
        StackTrace:
             at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
             at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)
             at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose)
             at System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady)
             at System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString)
             at System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async, Int32 timeout, Task& task, Boolean asyncWrite)
             at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean asyncWrite)
             at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(TaskCompletionSource`1 completion, String methodName, Boolean sendToPipe, Int32 timeout, Boolean asyncWrite)
             at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()
             at System.Data.Mapping.Update.Internal.DynamicUpdateCommand.Execute(UpdateTranslator translator, EntityConnection connection, Dictionary`2 identifierValues, List`1 generatedValues)
             at System.Data.Mapping.Update.Internal.UpdateTranslator.Update(IEntityStateManager stateManager, IEntityAdapter adapter)
        InnerException: 

代码如下

public virtual OperationResult Add(T entity)
    {
        OperationResult opStatus = new OperationResult { Result = QueryResult.Succeeded };

        try
        {
            DataContext.Set<T>().Add(entity);
            opStatus.Result = (DataContext.SaveChanges() > 0) ? QueryResult.Succeeded : QueryResult.Failed;
        }
        catch (Exception exp)
        {
            opStatus.ExceptionMessage = string.Format(" Error Adding {0}", exp.Message);
            opStatus.Result = QueryResult.Failed;
        }

        return opStatus;
    }

Answer 1

显然，entity 对象之前已经从数据库中获取了。如果将它添加到上下文中，它将得到 EntityState.Added，这意味着 EF 将尝试插入它。显然，您会在客户端生成一个主键值(即不在数据库中)，因此 EF 会尝试使用现有的 PK 值插入它。

因为这是 DbContext API(在 Set 方法中很明显，但总是有助于显式标记)，您可以使用 IDbSetExtensions.AddOrUpdate让 EF 确定对象是否需要插入或更新的方法。