ROXML from_xml not returning an object instance


#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”=>“11185.321521477119</
totalDist>640235.75000000000003</
totalMins>357865271635</
lonlaty>SH 71635 57865</
grcenter>false357290</
lonlatx>271650SH 71650 57290</
gridReference>812200</
distance>0false</
isLeg>357260274600</
lonlaty>SH 74600 57260275</
ascent>482950.152538429157</
distance>91false</
isLeg>359160273330</
lonlaty>SH 73330 5916073</
ascent>1702285.3664913969487</
distance>326false</
isLeg>359170270050</
lonlaty>SH 70050 59170182</
ascent>1723280.015243867016</
distance>270false</
isLeg>357470269740</
lonlaty>SH 69740 5747029</
ascent>1071728.0335644888382</
distance>190false</
isLeg>356840270440</
lonlaty>SH 70440 56840640</
ascent>717941.7536832951597</
distance>132”,
“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:insave’
/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:incall’
/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:increate’

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/

On Feb 4, 9:33 am, Ben W. removed_email_address@domain.invalid


#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.