How to implement a unique constrait in an Active Record migration

unique-constrait-on-active-record-migration.md

Here are the docs and here is a highly rated StackOverflow answer. (The docs are pretty long, you will probably want to search the web page for "unique" to find the relevant info.)

Bottom line: You need to create an index and make the index unique:

add_index :table_name, :column_name, :unique => true

Hope this helps. Any questions let me know.

-Phil