Having 'allocator undefined for Data' when saving with ActiveResource - ruby

Question

What I am missing? I am trying to use a rest service for with Active resource, I have the following:
class User < ActiveResource::Base
self.site = "http://localhost:3000/"
self.element_name = "users"
self.format = :json
end
user = User.new(
:name => "Test",
:email => "test.user#domain.com")
p user
if user.save
puts "success: #{user.uuid}"
else
puts "error: #{user.errors.full_messages.to_sentence}"
end
And the following output for the user:
#<User:0x1011a2d20 #prefix_options={}, #attributes={"name"=>"Test", "email"=>"test.user#domain.com"}>
and this error:
/Library/Ruby/Gems/1.8/gems/activeresource-3.0.10/lib/active_resource/base.rb:1233:in `new': allocator undefined for Data (TypeError)
from /Library/Ruby/Gems/1.8/gems/activeresource-3.0.10/lib/active_resource/base.rb:1233:in `load'
from /Library/Ruby/Gems/1.8/gems/activeresource-3.0.10/lib/active_resource/base.rb:1219:in `each'
from /Library/Ruby/Gems/1.8/gems/activeresource-3.0.10/lib/active_resource/base.rb:1219:in `load'
from /Library/Ruby/Gems/1.8/gems/activeresource-3.0.10/lib/active_resource/base.rb:1322:in `load_attributes_from_response'
from /Library/Ruby/Gems/1.8/gems/activeresource-3.0.10/lib/active_resource/base.rb:1316:in `create_without_notifications'
from /Library/Ruby/Gems/1.8/gems/activeresource-3.0.10/lib/active_resource/base.rb:1314:in `tap'
from /Library/Ruby/Gems/1.8/gems/activeresource-3.0.10/lib/active_resource/base.rb:1314:in `create_without_notifications'
from /Library/Ruby/Gems/1.8/gems/activeresource-3.0.10/lib/active_resource/observing.rb:11:in `create'
from /Library/Ruby/Gems/1.8/gems/activeresource-3.0.10/lib/active_resource/base.rb:1117:in `save_without_validation'
from /Library/Ruby/Gems/1.8/gems/activeresource-3.0.10/lib/active_resource/validations.rb:87:in `save_without_notifications'
from /Library/Ruby/Gems/1.8/gems/activeresource-3.0.10/lib/active_resource/observing.rb:11:in `save'
from import_rest.rb:22
If I user curl for my rest service it would be like:
curl -v -X POST -H 'Content-Type: application/json' -d '{"name":"test curl", "email":"test#gmail.com"}' http://localhost:3000/users
with the response:
{"email":"test#gmail.com","name":"test curl","admin":false,"uuid":"afb8c98b-562a-4603-bbe4-f8f0816cef0d","creation_limit":5}

Answer 1

There is a built-in type named Data, whose purpose is rather mysterious. You appear to be bumping into it:
$ ruby -e 'Data.new'
-e:1:in `new': allocator undefined for Data (TypeError)
from -e:1
The question is, how did it get there? The last stack frame puts us here. So, it appears Data wandered out of a call to find_or_create_resource_for. The code branch here looks likely:
$ irb
>> class C
>> end
=> nil
>> C.const_get('Data')
=> Data
This leads me to suspect you have an attribute or similar floating around named :data or "data", even though you don't mention one above. Do you? Particularly, it seems we have a JSON response with a sub-hash whose key is "data".
Here's a script that can trigger the error for crafted input, but not from the response you posted:
$ cat ./activeresource-oddity.rb
#!/usr/bin/env ruby
require 'rubygems'
gem 'activeresource', '3.0.10'
require 'active_resource'
class User < ActiveResource::Base
self.site = "http://localhost:3000/"
self.element_name = "users"
self.format = :json
end
USER = User.new :name => "Test", :email => "test.user#domain.com"
def simulate_load_attributes_from_response(response_body)
puts "Loading #{response_body}.."
USER.load User.format.decode(response_body)
end
OK = '{"email":"test#gmail.com","name":"test curl","admin":false,"uuid":"afb8c98b-562a-4603-bbe4-f8f0816cef0d","creation_limit":5}'
BORKED = '{"data":{"email":"test#gmail.com","name":"test curl","admin":false,"uuid":"afb8c98b-562a-4603-bbe4-f8f0816cef0d","creation_limit":5}}'
simulate_load_attributes_from_response OK
simulate_load_attributes_from_response BORKED
produces..
$ ./activeresource-oddity.rb
Loading {"email":"test#gmail.com","name":"test curl","admin":false,"uuid":"afb8c98b-562a-4603-bbe4-f8f0816cef0d","creation_limit":5}..
Loading {"data":{"email":"test#gmail.com","name":"test curl","admin":false,"uuid":"afb8c98b-562a-4603-bbe4-f8f0816cef0d","creation_limit":5}}..
/opt/local/lib/ruby/gems/1.8/gems/activeresource-3.0.10/lib/active_resource/base.rb:1233:in `new': allocator undefined for Data (TypeError)
from /opt/local/lib/ruby/gems/1.8/gems/activeresource-3.0.10/lib/active_resource/base.rb:1233:in `load'
from /opt/local/lib/ruby/gems/1.8/gems/activeresource-3.0.10/lib/active_resource/base.rb:1219:in `each'
from /opt/local/lib/ruby/gems/1.8/gems/activeresource-3.0.10/lib/active_resource/base.rb:1219:in `load'
from ./activeresource-oddity.rb:17:in `simulate_load_attributes_from_response'
from ./activeresource-oddity.rb:24
If I were you, I would open /Library/Ruby/Gems/1.8/gems/activeresource-3.0.10/lib/active_resource/base.rb, find load_attributes_from_response on line 1320 and temporarily change
load(self.class.format.decode(response.body))
to
load(self.class.format.decode(response.body).tap { |decoded| puts "Decoded: #{decoded.inspect}" })
..and reproduce the error again to see what is really coming out of your json decoder.

Answer 2

I just ran into the same error in the latest version of ActiveResource, and I found a solution that does not require monkey-patching the lib: create a Data class in the same namespace as the ActiveResource object. E.g.:
class User < ActiveResource::Base
self.site = "http://localhost:3000/"
self.element_name = "users"
self.format = :json
class Data < ActiveResource::Base; end
end
Fundamentally, the problem has to do with the way ActiveResource chooses the classes for the objects it instantiates from your API response. It will make an instance of something for every hash in your response. For example, it'll want to create User, Data and Pet objects for the following JSON:
{
"name": "Bob",
"email": "bob#example.com",
"data": {"favorite_color": "purple"},
"pets": [{"name": "Puffball", "type": "cat"}]
}
The class lookup mechanism can be found here. Basically, it checks the resource (User) and its ancestors for a constant matching the name of the sub-resource it wants to instantiate (i.e. Data here). The exception is caused by the fact that this lookup finds the top-level Data constant from the Stdlib; you can therefore avoid it by providing a more specific constant in the resource's namespace (User::Data). Making this class inherit from ActiveResource::Base replicates the behaviour you'd get if the constant was not found at all (see here).

Answer 3

Thanks to phs for his analysis - it got me pointed in the right direction.
I had no choice but to hack into ActiveResource to fix this problem because an external service over which I have no control had published an API where all attributes of the response were tucked away inside a top-level :data attribute.
Here's the hack I ended up putting in config/initializers/active_resource.rb to get this working for me using active resource 3.2.8:
class ActiveResource::Base
def load(attributes, remove_root = false)
raise ArgumentError, "expected an attributes Hash, got #{attributes.inspect}" unless attributes.is_a?(Hash)
#prefix_options, attributes = split_options(attributes)
if attributes.keys.size == 1
remove_root = self.class.element_name == attributes.keys.first.to_s
end
# THIS IS THE PATCH
attributes = ActiveResource::Formats.remove_root(attributes) if remove_root
if data = attributes.delete(:data)
attributes.merge!(data)
end
# END PATCH
attributes.each do |key, value|
#attributes[key.to_s] =
case value
when Array
resource = nil
value.map do |attrs|
if attrs.is_a?(Hash)
resource ||= find_or_create_resource_for_collection(key)
resource.new(attrs)
else
attrs.duplicable? ? attrs.dup : attrs
end
end
when Hash
resource = find_or_create_resource_for(key)
resource.new(value)
else
value.duplicable? ? value.dup : value
end
end
self
end
class << self
def find_every(options)
begin
case from = options[:from]
when Symbol
instantiate_collection(get(from, options[:params]))
when String
path = "#{from}#{query_string(options[:params])}"
instantiate_collection(format.decode(connection.get(path, headers).body) || [])
else
prefix_options, query_options = split_options(options[:params])
path = collection_path(prefix_options, query_options)
# THIS IS THE PATCH
body = (format.decode(connection.get(path, headers).body) || [])
body = body['data'] if body['data']
instantiate_collection( body, prefix_options )
# END PATCH
end
rescue ActiveResource::ResourceNotFound
# Swallowing ResourceNotFound exceptions and return nil - as per
# ActiveRecord.
nil
end
end
end
end

Answer 4

I solved this using a monkey-patch approach, that changes "data" to "xdata" before running find_or_create_resource_for (the offending method). This way when the find_or_create_resource_for method runs it won't search for the Data class (which would crash). It searches for the Xdata class instead, which hopefully doesn't exist, and will be created dynamically by the method. This will be a a proper class subclassed from ActiveResource.
Just add a file containig this inside config/initializers
module ActiveResource
class Base
alias_method :_find_or_create_resource_for, :find_or_create_resource_for
def find_or_create_resource_for(name)
name = "xdata" if name.to_s.downcase == "data"
_find_or_create_resource_for(name)
end
end
end