ActiveSupport #to_json doesn't work with DM

I also have this with ActiveRecord

@lawrence Can you provide an example where you are running into same problem with ActiveRecord.

I am able to reproduce this error with DM.

I guess if one of the instance variables refers back to the original object as is the case with the first example provided then I see two choices.

1) Let use pass an option :ignore_circular_reference => true. In this case in stead of raising an error, to_json method will ignore the circular reference and will move on.

2) Let user pass an option :ignore_items => _my_intance_variable. This will provide more control to user and rather than ignoring all circular references, user is asking to_json to ignore just this variable.

I hit the same thing with my models.
In my case, it fails if i attempt to call to_json on an activerelation object (i.e. church.where().to_json), but works if i do church.where().to_a.to_json

my model is:

class Church < ActiveRecord::Base
has_many :people has_many :groups validates_presence_of :name end

The only property it has is name.

Can someone provide a failing test using ActiveRecord? i've tried the thing that blackgold9 said but works for me ...
http://pastie.org/957044

The issue here is that ActiveSupport defines Object#to_json, and therefore Post.where.to_json tries to dump the ActiveRecord::Relation object instead of passing the method call on to it's internal collection. Note, this also applies to Object#to_yaml:

# script/rails console
include Test::Unit::Assertions

relation = Post.where # or Post.where(:author_id => 1), etc.

assert_nothing_raised(ActiveSupport::JSON::Encoding::CircularReferenceError) { relation.to_json } # fails
assert_nothing_raised(TypeError) { relation.to_yaml } # fails

ActiveRecord::Relation.send(:undef_method, :to_json)
ActiveRecord::Relation.send(:undef_method, :to_yaml)

assert_equal relation.to_a.to_json, relation.to_json # and now passes
assert_equal relation.to_a.to_yaml, relation.to_yaml # and now passes

This is important because it causes the following code to generate a 500 when requesting /posts/mine.json:

class PostsController < ApplicationController
  respond_to :html, :xml, :json
  def mine
    @posts = Posts.where(:author_id => 1)
    respond_with(@clients)
  end
end

Requiring "json/pure" solves the problem for DataMapper, you just need to implement to_json for your models (or for DataMapper::Model).

What Bernerd says.. exactly the issue I have. None of my controllers work when a json request is done. You'd think this workaround would work:

   def mine
     @posts = Posts.where(:author_id => 1).all
     respond_with(@posts)
   end

But that too fails in rails edge since a while, with "ArgumentError: wrong number of arguments (2 for 1)". Posts.where(:author_id => 1).to_yaml does work, Posts.where(:author_id => 1).to_json doesn't. I attempted to create a patch, but for some reason the delegation of to_json to to_a in ActiveRecord::Relation doesn't work. Anybody else have an idea?

(see attached what I tried; I also tried what Bernerd did, undef_method of to_json, same result)

I'm not sure if we should allow Post.where(:omg).to_json. If so, what about to_xml? And to_yaml?

This is still an issue with DataMapper 1.0.0 and Rails3 beta4. The above work-arounds using json/pure or dm-serializers don't work for me.

The test script by the original poster still fails.

Attached is patch with to_xml support. This patch needs be applied in addition to the patch previously mentioned.

How above ActiveRecord patch is supposed to solve serializing DataMapper objects??