find_one

# File activerecord/lib/active_record/relation/finder_methods.rb, line 432
    def find_one(id)
      if ActiveRecord::Base === id
        id = id.id
        ActiveSupport::Deprecation.warn(          You are passing an instance of ActiveRecord::Base to `find`.          Please pass the id of the object by calling `.id`.squish)
      end

      relation = where(primary_key => id)
      record = relation.take

      raise_record_not_found_exception!(id, 0, 1) unless record

      record
    end