[jruby-dev] Example persistence code

[Alan McKean]

Here is the sample code that I have been using to persist some simple  
objects:

To write persistent objects
require 'java'
require 'employee'
require 'persistence'

include Persistence

persistent 'people'
person = Person.new('Alan')
employee = Employee.new('Bob', 12345)
@people.store(person)
@people.store(employee)
person.children = Array.new
employee.children = Array.new
person.add_child(Person.new('Jesse'))
person.add_child(Person.new('Blake'))
employee.add_child(Person.new('Ben'))
@people.commit
puts 'Committed people'

To read persistent objects (in another VM)
require 'java'
require 'employee'
require 'persistence'

include Persistence

persistent 'people'
person = @people.fetch(0)
employee = @people.fetch(1)
puts 'Person name = ' + person.name
person.children.each {|child| puts 'child = ' <<  child.name}
puts
puts 'Employee name = ' + employee.name
puts 'Employee ssn = ' + employee.ssn.to_s
employee.children.each {|child| puts 'child = ' << child.name }

Here is the Persistence module
Note: the Indexable module and the extension to Array and Hash are  
only there to add an 'p_id' field for fetching by id in the example  
above
They will probably go away:

module Indexable
  def store_by_id(object)
    unless object.p_id
      object.p_id = self.size
    end
    self[object.p_id] = object
  end
end

class Array
  include Indexable
end

class Hash
  include Indexable
end

class PersistentRoot
  def initialize(indexable = Hash.new, options = {})
    @options = options
    @objects = indexable
  end

  def fetch(p_id, conditions = {})
    @objects[p_id]
  end

  def store(object)
    unless @@session.getTransactionService.inTransaction
      @@session.getTransactionService.beginTransaction
    end
    @objects.store_by_id(object)
  end

  def store!(object)
    unless @@session.getTransactionService.inTransaction
      @@session.getTransactionService.beginTransaction
    end
    @objects.store_by_id(object)
    commit
  end

  def commit
    @@session.commit
  end

end

module Persistence
  def self.included(otherModule)
    @@session = GsSessionImpl.getImpl 
(SessionFactory.getInstance.createNonPooledSession)
  end

  def persistent(name)
    rootObject = nil
    begin
      rootObject = @@session.getInitialContext.lookup(name)
    rescue
      @@session.begin
      rootObject = PersistentRoot.new
      @@session.getInitialContext.bind(name, rootObject)
      @@session.commit
    end
    instance_variable_set('@' + name, rootObject)
  end
end

Finally, the Person and its includes

module PID
  def p_id=(num)
    @p_id = num
  end
  def p_id
    @p_id
  end
end

module Family
  def children=(children)
    @children = children
  end
  def children
    @children
  end
  def add_child(child)
    @children << child
  end
end

class Person
  include PID
  include Family

  def initialize(name)
    @name = name
  end
  def name
    @name
  end
end