Persistent Objects with Ruby - simple beginning


#1

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 P. - Portfolio http://csmr.dreamhosters.com


#2

Casimir P. wrote:

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 might be interesting to compare your ideas with fsdb[1]. It does have
metadata for objects, but the only meta attr currently used is file
version.

[1] http://redshift.sourceforge.net/fsdb/doc/api/index.html


#3

Casimir P. wrote:

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’.

Have you looked at Madeleine?