Query example

announcements_query.rb

module Users
  class AnnouncementsQuery
    attr_accessor :used

    def initialize(user)
      @user = user
    end

    def unread
      active
        .joins(with_reads)
        .where(announcement_reads: { id: nil })
    end

    def read_later
      active
        .joins(with_reads(:inner))
        .where(announcement_reads: { read_later: true })
    end

    private

    def active
      Announcement
        .active
        .order(:started_at)
    end

    def with_reads(join_type = :left)
      case join_type
      when :left  then read_join 'LEFT OUTER'
      when :inner then read_join 'INNER'
      end
    end

    def read_join(type)
      <<~SQLJOIN
        #{type} JOIN
          announcement_reads
        ON
          announcement_reads.announcement_id = announcements.id
        AND
          announcement_reads.user_id = #{@user.id}
      SQLJOIN
        .squish
    end
  end
end