捕捉到 System.InvalidOperationException
_HResult=-2146233079
_message=意外的连接状态。在使用包装提供程序时，请确保在已包装的 DbConnection 上实现 StateChange 事件。
HResult=-2146233079
解决参考：
https://stackoverflow.com/questions/4867602/entity-framework-there-is-already-an-open-datareader-associated-with-this-comma
https://stackoverflow.com/questions/20693216/there-is-already-an-open-datareader-associated-with-this-connection-which-must-b
EF There is already an open DataReader associated with this Command
原文：http://www.cnblogs.com/mschen/p/7479087.html