From: Sean McEligot <sean.mceligot@...>
Date: 2005-03-05T01:31:41+09:00
Subject: Re: A wish: Simple database

> 1. Distributed as part of Ruby
> 2. Need not store entire db in memory
> 3. No SQL requirement
> 4. No special efficiency requirement
> 5. Available cross-platform
> 6. Database files are readable cross-platform

I just started on this YAML based database this week. The code is
below. I'm not sure where I'm going with this yet. It does not meet
requirement 2. I'm going to do a *dbm version also. That one will meet
requirment 2, but not 6. I'm also working a C++ database with
sleepycat here http://dbapi.sourceforge.net/ but that isn't ruby and
the ruby bindings aren't checked in.  Here's my simple yaml db. Maybe
it will give you some ideas.

#! /usr/bin/env ruby
require 'yaml'

$ydb_default_directory = "~"

class Ydb 
	def initialize(dbname, directory=$ydb_default_directory)
		@directory = File.expand_path(directory)
		@dbname = dbname
		@db = {}
		@modified = false
	end
	def load
		filename = db_filename
		if File.exists?(filename) then
			@db= YAML.load_file(filename)
		end
		@modified = false
	end
	def open
	 	load
	end
	def db_filename
		if not File.directory?(@directory) 
			p "mkdir: #{@directory}"
			Dir.mkdir(@directory)
		end
		File.join(@directory, @dbname+".yaml")
	end
	def []=(key,val)
		@db[key]=val
	end
	def [](key)
		@db[key]
	end
	def put(key,val)
		@db[key]=val
	end
	def put(obj)
		@modified||@modified = true
		if block_given?
			key = yield obj
		else
			key = obj.pk
		end
		@db[key]=obj
	end
	def has_key?(key)
		@db.has_key(keyk)
	end
	def each
		@db.each do |name, path|
			yield name, path
		end
	end
	def save
		if @modified then
			File.open( db_filename, 'w' ) do |out|
				YAML.dump( @db, out )
			end
		end
	end
	def close
		save
	end
	def keys
		@db.keys
	end
	def values
		@db.values
	end
	def index(name)
		ix = Ydb.new("#{@dbame}-#{name}")
		@db.keys.each do |key|
			val= @db[key]
			skey = yield val
			ix[key] = key
		end	
		return ix
	end
	def index!
		ix = {}
		@db.values.each do |val|
			key = yield val
			p "#{key}=#{val}"
			ix[key] = val
		end	
		return ix
	end
end

class TestItem 
	attr_accessor :id
	attr_accessor :fname
	attr_accessor :lname
	def initialize(id, fname, lname)
		@id = id
		@fname = fname
		@lname = lname
	end
	def pk
		@id
	end
	def to_s
		"#{id}:#{fname} #{lname}"
	end
end
def main
	if ARGV.length == 3 then
		db = Ydb.new("test")
		db.open
		row = TestItem.new(ARGV[0], ARGV[1], ARGV[2])
		db.put(row)
		db.close
	end

	db = Ydb.new("test")
	db.open
	db.each do |k,v| 
		p "#{k}=#{v}"
	end
	by_fname =db.index! do |i|
		i.fname
	end
	by_lname =db.index! do |i|
		i.lname
	end
	p "first names: #{by_fname.keys.join(" ")}"	
	p "last names: #{by_lname.keys.join(" ")}"	

	p "fdb"
	fdb=db.index("fname") do |i|
		i.fname
	end
	fdb.each do |k,v| 
		p "#{k}=#{v}"
	end
	db.close
end

if __FILE__ == $0
	main
end