query_class.rb

class BaseQuery
  attribute_accessor :object, :query

  def initialize
    @object = Null
    @query = [@object]
  end

  def execute
    @query.map.with_index { |q, i| i == 0 ? q : merge(q) }.join(send '.') # wtf
  end

  private

  def self.queries(*names)
    names.each do |name|
      define_method name do |*args|
        @query << send("_#{name}", args)
        self
      end
    end
  end
end

class NullQuery < BaseQuery
  queries :this, :that, :void

  private

  def _this(arg)
    joins(:something).where(something: { id: arg })
  end

  def _that
    where(thing: 1 || 2)
  end

  def _void
    where(:vampire > :werewolf)
  end
end

NullQuery.new.this(37).that.execute
#=> SELECT * FROM nulls INNER JOIN somethings WHERE somethings.id = 37 AND (nulls.thing = 1 OR nulls.thing = 2);