Model compatibility cannot be checked because the database does not contain model metadata

使用EF的时候映射数据的时候，出现了下面的问题。如图：

错误的提示为：Model compatibility cannot be checked because the database does not contain model metadata.Model compatibility can only be checked for databases created using Code First or Code First Migrations.

解决方法：

USE [master]
GO

/****** Object: Database [DBname] ******/
 ALTER DATABASE [DBname] SET SINGLE_USER WITH ROLLBACK IMMEDIATE
 ALTER DATABASE [DBname] SET SINGLE_USER WITH NO_WAIT
 DROP DATABASE [DBname]
 GO

DBname 即为你的数据库名称，执行完上面的这段Sql语句，上面出现的问题就解决了。