How to stored the id value by selecting another value from Dropdown

Hello, I have a course table with field as Course Id and Course Name. In the another screen, I am having drop down which shows the Course Name for user convenience, but once the user select the Course Name, I want to store it Course Id internally in the table. Course Id : 100 Course Name : English  Once the user select English, I wish to store 100 in my table.  Please advise how to do it.    
1 answers

I used reference selector and created association between my entities as a result I don’t to save any reference field and can refer them by my association.