How to make the validation that only accepts lower case 'a-z' and number '0-9'

Question

I have my app and it has username column. For user input, I'd like to make this column with validation.

username has to contain only the characters below

abcdefghijklmnopqrstuvwxyz0123456789

Answer 1

Use a format validator:

validates :username, format: { with: /\A[a-z0-9]+\z/ }

https://guides.rubyonrails.org/v3.2/active_record_validations_callbacks.html