It looks like that either the Postgres Reader and Writer doesn't support multiple column / field constraints. See discussion:
If you ask me it's a shortcomming that should be fixed!
Open
Support multiple column / field constraints for Postgres Reader and Writer
+8- Safer
Hello!
I talk about this feature with our Database development team. As you know, FME doesn’t support creating composite constraints for indices. The workaround is to use SQL to either:
- Create the table with the desired constraints before writing
- if you prefer, add them after writing, if you’re confident the written data will be compliant.
A good way to do this is to use SQL to Run Before Write on your writer, and then select Table Handle = Use Existing Existing Table in the writer feature type. If you need to use more than one SQL statement to do this, read the doc for FME_SQL_DELIMITER