just_and_exactly.rb

# frozen_string_literal: true

require "active_record"

module JustAndExactly
  module ActiveRecordExtensions
    MultipleRecordsFound = Class.new(ActiveRecord::ActiveRecordError)

    # Like +first!+, but will also fail if the query would match more than
    # one record.
    def exactly_one!
      results = find_nth_with_limit(0, 2)
      raise ActiveRecord::RecordNotFound, "Couldn't find #{@klass.name} with [#{arel.where_sql}]" \
        if results.empty?

      raise MultipleRecordsFound, "Query returned more than one result for [#{arel.where_sql}]" \
        if results.size > 1

      results.first
    end

    # Like +find+, but will fail if the query would match more than one record.
    def just_one
      exactly_one!
    rescue ActiveRecord::RecordNotFound
      nil
    end
  end
end

ActiveRecord::Relation.include JustAndExactly::ActiveRecordExtensions