如何将文件名更改为主键ID？

So I have a program that the user inputs text into a text box, and then that text is created into a file. Each time the submit button is pressed, the database creates a job and is given a jobID. I was wondering if there was anyway to make the name of the file the job_id.fasta instead of just calling it new.fasta. This way I am able to store more files! Thanks in advance. I will post the code of creating the file and storing it.So I have a program that the user inputs text i