这是实体框架的一部分,需要添加引用EntityFramework.dll
如果还没装实体框架去这里下
http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=8363
You dont have to import System.Data.Entity.Database. The System.Data.Entity is enough. Use Database.SetInitializer instead of DbDatabase.SetInitializer