how to get most recent document uploaded in grid.I have created grid with 3 columns ,in which how to get most recent document which is uploaded by user.
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Do you mean that a User can upload 3 different documents into your interface in any order and you want to know which was the latest one they uploaded? When you execute the saveInto() on your a!fileUploadField() you could execute an additional a!save() and store the value of fn!now() into a local variable, one for each of the files the user can upload. You can then compare the local variables to determine which was the latest.
do we get documentation on the same?
All of the needed functions are documented in the Appian Functions Documentation among other places. I'm afraid people here won't generally be able to write your code for you, especially without either a specific problem/issue to report, and/or a better-described use case, at least.