Can anyone help me in validating the fields entered in the form with the details that are already existing in the database.
like entered details and existing details are matched then some functionality need to be performed.
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My first question is what are you trying to achieve? If you have data about anything (a User in your example) and you want to validate fields being entered about that data, why aren't you simply retrieving the data you already have, rather than having someone enter the same data and then checking if it's correct? What's the Use Case here?
Actually I have created a user management application in appian and in that i have created registration page and storing the values of the registered users in database .Now I have created a login page also.Now my problem is I have username and password fields in login page when entered values in those fields , the values should get compared with those in registered database table.If entered values are equal to values in database they should login and redirect to another page otherwise throw an error.
So now my next question is: why are you replicating a User Authentication capability that already exists within Appian?
Because I need a separate registration and login interface for my application
Why would a user need to log in for your application when they've already been authenticated by Appian login? At this point the normal design is to simply expose to them any application(s) they're eligible to see - all information that should be tracked inside Appian already.