ruby on rails - Check if attribute is unique across two columns -

my classroom model has 2 attributes, student_classcode , teacher_classcode. have after_create callback generate these 2 codes after classroom created. currently, generate student_classcode far this:

(taken here)

class classroom < activerecord::base    after_create :generate_token    private      max_retries = 10     def generate_token       update_column :student_classcode, securerandom.hex(4)     rescue activerecord::recordnotunique => e       @token_attempts = @token_attempts.to_i + 1       retry if @token_attempts < max_retries       raise e, "retries exhausted"     end  end 

right makes sure student_classcode unique (with 10 retries). want able generate teacher_classcode well, , want make sure unique among teacher_classcode column and student_classcode column.

so example, if classroom has student_classcode '12345', , (by chance) teacher_classcode of classroom b generates '12345', want classroom b regenerate classcode. or, if classroom b has student_classcode 'abcde', , classroom b has teacher_classcode 'abcde', want classroom b regenerate teacher_classcode.

i know chances of there being 2 of same classcode across both columns small, don't want take chances. how can that?

why don't make classcode model in own right, validations ensure code unique. generate generic code , through standard belongs_to associations classroom can associate teacher , student classcode.

this way can sure each classcode unique , have 1 implementation of code generation.