Staging table "insert" method doesn't get a call while inserting records from txt file to staging table in Dynamics ax 2012 DMF

Hi, I am looking out a way to call the standard methods e.g. initValue(), insert() etc in staging table while inserting records from text file to staging table in Dynamics ax 2012 R3 data import export framework.  In my case, I added few logic in insert() in staging table which doesn't get executed during staging data upload. Any feedback will be appreciated. 

Thanks in advance.