ruby on rails - How do you deal with the conflict between ActiveSupport::JSON and the JSON gem?

Question

I am stumped with this problem.

ActiveSupport::JSON defines to_json on various core objects and so does the JSON gem. However, the implementation is not the same -- the ActiveSupport version takes arguments and the JSON gem version doesn't.

I installed a gem that required the JSON gem and my app broke. The issue is that I'm using to_json in a controller that returns a list of objects, but I want to control which attributes are returned.

When code anywhere in my system does require 'json' I get this error message:

TypeError: wrong argument type Hash (expected Data)

I tried a couple of things that I read online to fix it, but nothing worked. I ended up re-writing the gem to use ActiveSupport::JSON.decode instead of JSON.parse.

This works but it's not sustainable...I can't be forking gems every time I want to use a gem that requires the JSON gem.

Update: The best solution of this problem is to upgrade to Rails 2.3 or higher, which fixed it.

Answer 1

UPDATE: Even with Rails 3.2, the same problem remains unfixed. The nasty hack to forcibly load the json gem and overwrite it, that is.

Eventually I ended up with the following code, to entirely bypass ActiveSupport's to_json completely. Put it in config/initializers/patches.rb, and you can do {}.jsonize or [].jsonize to generate JSON string. No conflicts with anything, guaranteed.

# Undo the effect of 'active_support/core_ext/object/to_json'
require 'json'
[Object, Array, Hash].each do |klass|
  klass.class_eval <<-RUBY, __FILE__, __LINE__
    def jsonize(options = nil)
      ::JSON.generate self, :quirks_mode => true
    end
  RUBY
end

The 8 lines of code make your app 50 times faster for JSON encoding. Probably you want to do the same. :)

---

I've been having a similar problem up until Rails 2.3.8.

The problem is that ActiveSupport::JSON.backend = 'JSONGem' is a half-assed solution and you still need to overwrite some encoders yourself. (WARNING: for Rails 3.x, which uses MultiJson, it must be ActiveSupport::JSON.backend = :json_gem at least, or it will be silently no-op.)

In my case, I needed to overwrite String#to_json because JSON gem 1.4.3 is better in that it doesn't blindly encode non-ascii-but-valid-UTF8 characters in the form of "uXXXX" where it's not necessary, so you get shorter bytes (good for serialization) and easy-to-read results ("日本語" looks much sexier to my eyes than "u65e5u672cu8a9e").

Here's the monkey patch that I've been using - put the following code in config/initializers/patches.rb

module ActiveSupport
  module JSON
    module Encoding
      class << self
        def escape(string)
          ::JSON.generate([string])[1..-2]
        end
      end
    end
  end
end

and you're free to use to_json on anything - String, Array and Hash.