From: Casimir Pohjanraito <piksNOSeliPAM@...>
Date: 2008-12-17T03:22:35+09:00
Subject: Persistent Objects with Ruby - simple beginning

Object persistence, I want it, without SQL or other schemes that could be 
implemented in ruby and somewhat automated instead. Smalltalk and Squeak 
inspired. Objects exist, no CRUD or 'saving' or 'writes'.

So, as an attempt to I made this Storage singleton and Storable -class. 
(code at end or at http://pastie.org/340631 )

It is very simple and crude. I am not a computer scientist, more like an 
artist with tourettes.

Nevertheless, I was hoping to get input. I think perhaps the next step 
would be changing this into a module.

If time and skills permit it, it would be fun to make a ruby fork with 
persistence similar to Prevayler (mem + snapshots&transactions record) or 
Squeak (save image of VM), like DHH suggested in 2k8 Rubyconf:

Persruby.

Have fun,
Casimir

#start START
#See example at end of file. Paste into IRB or save as file and load to 
test.

class Storable

  #Marshals objects, creates meta-data labels
  #Intent: abstracts marshaling, unique filename, structured labeling
  #ORM-like?

  
attr_accessor :filename, :label, :label_str, :user, :private, :tags, :description

  def initialize(given_name = "unknown_object") 
    @creation_time = Time.now.tv_sec
    @given_name = given_name.to_s
    @tags = "storable" #for metainfo
    @description = "desc"

    #generate label
    self.labelize()

    #generate filename
    filename_str = @given_name +"."+ self.object_id.to_s 
# +"."+ @creation_time.to_s
    filename_str = filename_str.gsub(" ", "_")
    @filename = filename_str #why this again?!?
  end #init

  def labelize #sets storable's attribs for the purposes of labeling them
    @label = {
    	#   - object class
    	:class => self.class.to_s,
    	# 	- given name
    	:given_name => @given_name,
    	# 	- object id
    	:object_id => self.object_id.to_s,
    	#   - time created
    	:time_created => @creation_time.to_s, #seconds since epoch
    	# 	- owner
    	:user => "user",
    	#   - tags_str
    	:tags => @tags.to_s,
    	#   - description_str
    	:description => @description.to_s
    	#   - date now (filesystem?)		
    }
    
    #Label packaged to a String -form
    @label_str = ""
    self.label.each_pair { |key, val|
    	#each pair into string delimited by |
    	label_str << key.to_s + "|" + val.gsub("|", "!").to_s + "\n"
    }

  end #end labelize

  def put_into_storage
  #marshals, labels and stores object in Storage
    #future args command_msg_str
    #set object label
    labelize()
    #marshal object
    package = Marshal.dump(self)
    #store label and object
    #resolve 'storage path'
    relative_path_str = "serialized." + self.class.to_s + "." + 
@filename.to_s

    #store label
    lbl_path = relative_path_str + ".label"
    Storage.store(lbl_path, @label_str)
    
    #store file
    Storage.store(relative_path_str, package)
  end

   def self.find_by_fname(fname) #not implemented 
     found = nil  
     ObjectSpace.each_object(Object) { |o|  
       found = o if o.fname == fname  
     }  
     found  
  end

end #Class Storable

# Storage.rb - datastore-module
# - Storage abstraction 1st. Scalability 2nd.
# - gold spike: store marshaled objects
# - future store YML -objects in a namespace of some kind.
# - future SQL

#Roadmap
# DB/QL support
# I. Marshall objects
#     - serialize/re-instance
#     - namespace?
# II. Yaml/JSON/XML
# III. ODB?
# IV. MySQL and so on
#
#Inteface Roadmap
#   * Make a module instead of inheritable?!?
#   * store.config. Configurable parameters.
#   * Store object.
#   * Retrieve object.
#   * Sort/Compare/etc

require "singleton.rb"

class Storage 

  include Singleton

  #Instantiated with:
  #Storage = Storage.instance
  #
  #Requires:
  #writable storage_home_local_path -directory
  #Object to be stored is of class storable
  #
  #Usage:
  #Storage.store(object, path_str)
  #
  #Returns:
  #future: status code indicating the result
  
  #TODO move this to config-file

  @@storage_home_local_path = '/tmp/'

  attr_reader :storage_home_local_path 

  ### Constructor ###############################
  def initialize() 

  end #init

  def set_storage_configuration()
  end

   ### CLASS METHODS #############################
  def self.store(relative_path_str, content_string)
    store_content_string(relative_path_str, content_string)
   end

  def self.store_content_string(relative_path_str, content_string)
    	target_path = @@storage_home_local_path + relative_path_str
      #print target_path
      wf_io = File.open(target_path, "w")
    	wf_io.write(content_string)
        unless wf_io.closed?
          #wf_io.flush()
    		  wf_io.close()
      end
  end

  def self.query(selector_str, keyword_str)

    case selector_str
      when "by_path"
        items = Dir[@@storage_home_local_path + keyword_str]
        labels = Dir[@@storage_home_local_path + keyword_str + ".label"]
        items = items-labels

      when "by_class"
    		#etc etc
  
    end #case
  end

  def self.unpack(relative_path_or_filename_str)  
    #returns unpacked stored object
    #resolve path
    relative_path_or_filename_str = relative_path_or_filename_str.gsub
(@@storage_home_local_path, "") #remove path in case exists so no dbl path
    target_path = @@storage_home_local_path + 
relative_path_or_filename_str.to_s

    begin 
      open(target_path) do |f|
      @loaded_object = Marshal.load(f)
      end
    rescue StandardError => crash
      print "Storage unpack: Standard Error opening file "
      print target_path.to_s + ", returned: " + crash + ". "
    end
    
    return @loaded_object
  end

end #e Storage

#Example code

Storage.instance #a instance of the Storage

class Tester < Storable
  def initialize(some_str)
    super()
    @stuff = Array.new
    20.times { @stuff.push(some_str.to_s) }
  end

  attr_reader :stuff
end

this_test = Tester.new("Test for comp.lang.ruby")
this_test.put_into_storage()
print this_test = "blah"

presumed_obj = Dir["/tmp/**unknown_object**"][0].to_s
unserred = Storage.unpack(presumed_obj)
print unserred.inspect()
print unserred.stuff #??!??

#end END END


Casimir Pohjanraito - Portfolio http://csmr.dreamhosters.com