The major issue here is that datepart is expected to be a keyword - but the default rendering of the sql will produce a literal. This adds some difficultly in mapping to a user defined function.
SQLServer translator already maps the timestampadd system function to the SQLServer dateadd function and handles the source sql for you. Is there a reason you don't want to use the system timestampadd function?
Thanks for response . You are right. Even I realized this after posting it in forum. Initially I tried executing timestampadd in SQL server directly, which was not working.so thought it is not supported by sql server. So ended up exploring other options which took me to DateAdd & pushing same to source.
Sorry for confusion.