server.rb

module SoftDelete
  REQUIRED_PROPERTIES = [
    [ :deleted_at,  DataMapper::Property::DateTime ],
  ].freeze

  def self.extended(klass)
    REQUIRED_PROPERTIES.each do |property|
      klass.send(:property, *property)
    end

    klass.send(:extend, SoftDelete::ClassMethods)
    klass.send(:include, SoftDelete::InstanceMethods)
  end

  module ClassMethods
    def active
      self.all(deleted_at: nil)
    end
  end

  module InstanceMethods
    def active?
      !!self.deleted_at
    end

    def destroy
      self.deleted_at = Time.now; save_self(true)
    end
  end
end

# Instead of writing all of this...
class Server
  property :deleted_at, DataMapper::Property::DateTime

  def self.active
    self.all(deleted_at: nil)
  end

  def active?
    !!self.deleted_at
  end

  def destroy
    self.deleted_at = Time.now; save_self(true)
  end
end

# All we have to write is this
class Server
  extend SoftDelete
end

# And we can reuse the code here
class Volume
  extend SoftDelete
end