Cannot attach the file as database这个异常是在EF的code frist里经常出现的，解决方法很简单，只要重新启动一下V11实例即可。
CMD> sqllocaldb.exe stop v11.0 LocalDB instance "v11.0" stopped. CMD> CMD> sqllocaldb.exe delete v11.0 LocalDB instance "v11.0" deleted. CMD> sqllocaldb.exe start v11.0 LocalDB instance "v11.0" started.
再次运行应用程序，搞定！
EF架构~Cannot attach the file as database
原文：http://www.cnblogs.com/lori/p/5206687.html