How do I refer to APP_Data from another project

connectionString="Data Source=.SQLExpress; Integrated Security=true; AttachDbFilename=C:MySolutionMyMVCProjectApp_DataMyDatabase.mdf"

connectionString="Data Source=.SQLEXPRESS;AttachDbFilename=|DataDirectory|MyDatabase.mdf;Integrated Security=True;User Instance=True"

connectionString="Data Source=.SQLExpress; Integrated Security=true; AttachDbFilename=" & Server.MapPath("~App_DataMyDatabase.mdf")