ROXML from_xml not returning an object instance...

rubyonrails-talk
1

Hello,

I have two ActiveRecord classes. One is Route the other is Waypoints. I have constructed an XML representation so I can use AJAX to create a Route with all waypoints in a single create call to RouteController. When I call Route.from_xml(xmlString) it is not returning an object - it's leaving the object (@route) nil, but not erroring. Any ideas? Here's some code:

RoutesController:

  def create     @route = nil;     if params[:requestXML]

      # unserialise from XML using ROXML       @route = Route.from_xml(params[:requestXML]);

    else       @route = Route.new(params[:route])     end

    respond_to do |format|

     #The following line unsurprisingly fails, as @route is nil       if @route.save

        flash[:notice] = 'Route was successfully created.'         format.html { redirect_to(@route) }         format.xml { render :xml => @route, :status => :created, :location => @route }         format.js       else         format.html { render :action => "new" }         format.xml { render :xml => @route.errors, :status => :unprocessable_entity }       end     end   end

Route.rb:

class Route < ActiveRecord::Base   include ROXML

  has_many :waypoints

  xml_reader :title   xml_reader :totalDist   xml_reader :totalMis   xml_reader :totalHg   xml_reader :lonlatx   xml_reader :lonlaty   xml_reader :grcenter

  xml_accessor :waypoints, [Waypoint], :in => "waypoints" end

Waypoint.rb:

class Waypoint < ActiveRecord::Base   include ROXML

  belongs_to :route

  xml_reader :isLeg   xml_reader :lonlatx   xml_reader :lonlaty   xml_reader :gridReference   xml_reader :ascent   xml_reader :descent   xml_reader :distance   xml_reader :bearing   xml_reader :timemins end

NB I've not specified types at the moment for the above elements. I'm just trying to verify that the XML is being parsed by ROXML's from_xml method.

Error Message in logs:

Processing RoutesController#create (for 127.0.0.1 at 2009-02-03 16:36:12) [POST]   Session ID: BAh7DToMY3NyZl9pZCIlZWY5NWRjODFjMTI5ZDg3ZDlhZGRjODM0ODA3NmZl YTE6DW5hdnN0YWNrWwYiBi86DnJldHVybl90byIaL2FkYW1mb3dsZXIvZGFz aGJvYXJkOhBsYXN0X2FjdGl2ZVU6IEFjdGl2ZVN1cHBvcnQ6OlRpbWVXaXRo Wm9uZVsISXU6CVRpbWUNb0MbgAAAwMEGOh9AbWFyc2hhbF93aXRoX3V0Y19j b2VyY2lvblQiCFVUQ0AMOgl1c2VyaRM6C2ZvcnVtc3sAOgt0b3BpY3NADiIK Zmxhc2hJQzonQWN0aW9uQ29udHJvbGxlcjo6Rmxhc2g6OkZsYXNoSGFzaHsG Ogtub3RpY2UiJFJvdXRlIHdhcyBzdWNjZXNzZnVsbHkgY3JlYXRlZC4GOgpA dXNlZHsGOxBU--48a6d44f6baa5129fd1160815273a9c30ca746a8   Parameters: {"requestXML"=>"<route><totalDist>11185.321521477119</

<totalHg>640</totalHg><totalMins>235.75000000000003</ <lonlatx>357865</lonlatx><lonlaty>271635</ <grcenter>SH 71635 57865</ <waypoints><waypoint><isLeg>false</isLeg><lonlatx>357290</ <lonlaty>271650</lonlaty><gridReference>SH 71650 57290</ <ascent>81</ascent><descent>220</descent><distance>0</ <bearing>0</bearing></waypoint><waypoint><isLeg>false</ <lonlatx>357260</lonlatx><lonlaty>274600</ <gridReference>SH 74600 57260</gridReference><ascent>275</ <descent>48</descent><distance>2950.152538429157</ <bearing>91</bearing></waypoint><waypoint><isLeg>false</ <lonlatx>359160</lonlatx><lonlaty>273330</ <gridReference>SH 73330 59160</gridReference><ascent>73</ <descent>170</descent><distance>2285.3664913969487</ <bearing>326</bearing></waypoint><waypoint><isLeg>false</ <lonlatx>359170</lonlatx><lonlaty>270050</ <gridReference>SH 70050 59170</gridReference><ascent>182</ <descent>172</descent><distance>3280.015243867016</ <bearing>270</bearing></waypoint><waypoint><isLeg>false</ <lonlatx>357470</lonlatx><lonlaty>269740</ <gridReference>SH 69740 57470</gridReference><ascent>29</ <descent>107</descent><distance>1728.0335644888382</ <bearing>190</bearing></waypoint><waypoint><isLeg>false</ <lonlatx>356840</lonlatx><lonlaty>270440</ <gridReference>SH 70440 56840</gridReference><ascent>640</ <descent>717</descent><distance>941.7536832951597</ <bearing>132</bearing></waypoint></waypoints></route>",

"authenticity_token"=>"a538a4ed8056e17ded2904abfb00628ff6594a07", "action"=>"create", "controller"=>"routes"} [globalite] loading locale: en-US from config [globalite] Locale set to en-US [globalite] loading locale: en-US from config [globalite] Locale set to en-US

NoMethodError (You have a nil object when you didn't expect it! You might have expected an instance of Array. The error occurred while evaluating nil.delete):     /Library/Ruby/Gems/1.8/gems/activerecord-2.1.2/lib/active_record/ transactions.rb:124:in `rollback_active_record_state!'     /Library/Ruby/Gems/1.8/gems/activerecord-2.1.2/lib/active_record/ transactions.rb:106:in `save'     /app/controllers/routes_controller.rb:52:in `create'     /Library/Ruby/Gems/1.8/gems/actionpack-2.1.2/lib/action_controller/ mime_responds.rb:106:in `call'     /Library/Ruby/Gems/1.8/gems/actionpack-2.1.2/lib/action_controller/ mime_responds.rb:106:in `respond_to'     /app/controllers/routes_controller.rb:51:in `create' ...

Thanks,

Adam.

2

Hey Adam,

I'll take a look at this later today and get back to you. I specifically haven't tested intermixing ROXMl and ActiveRecord (as you have with :waypoints). I suspect the problem is that I'm setting the instance variable rather than going through the proxy accessor. I'll post here again when I have that worked out.

Or, if you're so inclined, you can dig into the code yourself. See the "instance_variable_set" line, line 586 here: http://github.com/Empact/roxml/blob/c9a3d82827d6939fcc76fa354a52f8bc357ba169/lib/roxml.rb

3

Alright, the problem seems to be that ROXML uses the Object#allocate to generate objects, and never calls #initialize on those objects, owing to the fact that you would want to initialize differently in a world where your attributes are already initialized than in one where they are not (which is the base #new case). There's a workaround though, which I haven't tested but which will definitely solve the immediate problem. That is to implement the #xml_initialize method on your objects, and in it, call the regular #initialize, like so:

class RoxmlClass < ActiveRecord::Base   include ROXML   def self.xml_initialize     initialize   end end

#xml_initialize (http://roxml.rubyforge.org/rdoc/classes/ROXML/ InstanceMethods/Construction.html#M000010) is called at the end of #from_xml, and can be used to do things like call initialize with the data from your xml attributes, or whatever else.

Hope that helps, and I'll have something which handles this in a general way out in the near future. Feel free to contact me directly in the future. You'll find my email on the website: http://empact.github.com/roxml/

4

Alright, I found that this actually required a bit more to work properly, but if you look at my latest code: http://github.com/Empact/roxml/tree/master, I have a examples/active_record.rb, and spec/examples/active_record.rb to show it's working properly.

So install this latest version from my github and you should have things working. See the history: http://github.com/Empact/roxml/blob/a2434d5c14a31ec2099c38a6248b4fcf4e5f5565/History.txt for the changes involved.

You should also get some deprecation warnings from this newest code. I'm preparing for a bit of an API shakeup in 3.0 which should be the last. In short, all type declaration come via the :as parameter, all location declarations come via :from and :in, all options come as separate arguments. The rdocs should be up to date on this.