how use app.confi

sir

string connectionString =(string)ConfigurationSettings.AppSettings["SanaSoh"];
this line run on page rightly but when i run in class then it give me a error
somebody give me idea for app.cofing file
i use app.cofing file and give path of me database but no access databasse in class
please give me idea how i use database in class form win.confing by using app.conging or directly


thank you






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