Take a backup of the database on 2008R2, example shown below:

USE Master

GO

BACKUP DATABASE [SQLTraining]

TO DISK = N'D:\SQLTraining_FullBackup.bak' WITH NOFORMAT, NOINIT,

NAME = N'SQLTraining-Full Database Backup', SKIP, NOREWIND, NOUNLOAD, STATS = 10

GO

Restore the same on 2012 box

USE master

GO

RESTORE DATABASE [SQLTraining2012] FILE = N'SQLTraining'

FROM DISK = N'D:\SQLTraining_FullBackup.bak'

WITH FILE = 1,

MOVE N'SQLTraining'

TO N'D:\SQLTraining2012.mdf',

MOVE N'SQLTraining_log' TO N'D:\SQLTraining2012.LDF',

NOUNLOAD, STATS = 10

GO

This works like charm 🙂