Could you please set an example for us? Are you try to retrieve your table schema in runtime?
If you want to build schema at the runtime, please have a look at the subscription solution of Talend to get access to dynamic schema functionality.
Talend named a Leader.
Kickstart your first data integration and ETL projects.
Learn how to do cool things with Context Variables
Find out how to migrate from one database to another using the Dynamic schema
Pick up some tips and tricks with Context Variables