A small extension to `sequel` to add a #one method to Dataset

sequel_one_extension.rb

# frozen_string_literal: true
#
# The one extension adds Dataset#one which performs a LIMIT(2) query and will raise a
# Sequel::NoMatchingRow if exactly one row is not returned.

module Sequel
  module One
    MSG = 'Expected query to produce exactly 1 row but received %<rows>s.'

    def one
      rows = fetch_two

      return rows.first if rows.one?

      fail NoMatchingRow, format(MSG, rows: rows.size)
    end

    private

    def fetch_two
      limit(2).all
    end
  end # One

  Dataset.register_extension(:one, One)
end # Sequel

Thank you very much for the gist. I found it very useful. I reformatted it based on the instruction found here

module Sequel
  module Plugins
    module One
      module DatasetMethods
        MSG = 'Expected query to produce exactly 1 row but received %<rows>s.'

        def one
          rows = fetch_two

          return rows.first if rows.one?

          fail NoMatchingRow, format(MSG, rows: rows.size)
        end

        private

        def fetch_two
          limit(2).all
        end
      end
    end
  end
end