snippet.rb

# PROBLEM SYNOPSIS
# 
# Updating the  has n :faqs  association key :faq_category_id inside a before block in the parent modeL
# DOES NOT WORK
# 
# It does however work outside of the before block.
# 
# 

%w( rubygems dm-core dm-validations dm-timestamps dm-types dm-is-list dm-is-tree ).each { |lib| require lib }


class FaqCategory 
  include DataMapper::Resource
  property :id,                         Serial, :key => true 
  property :parent_id,                  Integer, :required => true
  property :name,                       String, :length => 100, :required => true 
  
  has n, :faqs
  
  # is :list, :scope => [:parent_id], :order => [:position]
  # is :tree, :order => [:parent_id, :position]
  
  before :destroy do 
    
    # WORKING CODE
    # faqs.map(&:id).each do |f|
    #   Faq.get(f).update(:faq_category_id => self.parent_id)
    # end
    
    # throws [ DataMapper::UpdateConflictError: Faq#update cannot be called on a dirty resource " ]
    # faqs.update(:faq_category_id => parent_id)
    
    ## doesn't update the faq_category_id on save
    faqs.each do |faq|
      faq.faq_category_id = parent_id
      puts faq.errors.inspect
      faq.save
      puts "faq.faq_category_id after save was faq.faq_category_id=[#{faq.faq_category_id}] [#{__FILE__}:#{__LINE__}]"
    end
    
    puts "faqs.class=[#{faqs.class}] [#{__FILE__}:#{__LINE__}]"
    # unless children.empty?
    #   # children.map(&:id).each do |child_id|
    #   #   FaqCategory.get(child_id).update(:parent_id => self.parent_id)
    #   # end
    #   children.map(&:id).each { |child_id| FaqCategory.get(child_id).update(:parent_id => self.parent_id) }
    # end      
  end
  
end

class Faq 
  include DataMapper::Resource
  property :id,                         Serial
  property :faq_category_id,            Integer, :required => true
  property :question,                   String, :length => 250, :required => true 
  
  belongs_to :faq_category
  # is :list, :scope => [:faq_category_id]
  
end


DataMapper::Logger.new("#{File.dirname(__FILE__)}/dm-faqs-problem.log", :debug)
DataMapper.logger.debug "Using DataMapper::VERSION=[#{DataMapper::VERSION}]"

DataMapper.setup(:default, 'sqlite3::memory:')
DataMapper.logger.debug "begin bootstraps #====================#\n"
DataMapper.auto_migrate!

@a = FaqCategory.create(:parent_id => 0, :name => "A")
@b = FaqCategory.create(:parent_id => 0, :name => "B")
@aa = FaqCategory.create(:parent_id => @a.id, :name => "Aa")
@ab = FaqCategory.create(:parent_id => @a.id, :name => "Ab")

## add some FAQs
Faq.create(:faq_category_id => @a.id, :question => "A1")
Faq.create(:faq_category_id => @b.id, :question => "B1")
DataMapper.logger.debug "end bootstraps #====================#\n"

## UPDATING THE :faq_category_id MANUALLY OUTSIDE OF A BEFORE BLOCK

faq = Faq.get(2)
puts faq.inspect   # should show faq_category_id being 2
faq.faq_category_id = 0
faq.save

puts faq.inspect # should show faq_category_id being 0


## THE PROBLEM CODE COMES HERE>>>>
## UPDATING THE :faq_category_id INSIDE A BEFORE BLOCK IN THE PARENT MODEL

puts Faq.get(1).faq_category.inspect  # should show the FaqCategory
puts Faq.get(1).faq_category_id # should show 1

f = FaqCategory.get(1)
puts f.inspect
# puts f.children.inspect
# puts f.children.first.inspect
# puts fc_child.inspect

f.destroy

puts Faq.get(1).faq_category_id  # should show it as 0
puts Faq.get(1).inspect 

%w(Aa Ab).each do |name|
  puts FaqCategory.first(:name => name).inspect
end