如果数据库已连接，请转到Management Studio并将数据库与SQL Server实例分离.之后，您的代码应该可以在运行数据库时附加数据库.

If the database is already attached, go to Management Studio and detach the database from the SQL Server instance. After that your code should be able to attach the database when you run it.

开发者社区1号连接字符串参考

Developers community number 1 connection string reference