使用触发器在PostgreSQL中复制自动增量生成的字段

I have a problem about using trigger in PostgreSQL to create bar-code. The problem is that when Client Side access my web app and insert data in the same time, I need generate bar-code in some my purpose project. But the problem is that the Auto generated bar-code is Duplicate. Any solution, please help me. format bar-code is: I have a problem about using trigger in Postgre