ActiveSupport::JSON.encode is Inconsistent for #as_json and #to_json

I am also having the same issues with 3.0.0.beta3 with ruby 1.9.1p378.

@Huet most likely you already know that rails3 does not support ruby 1.9.1. Officially rails3 is supported on ruby 1.9.2 .

Assigning it to Mr. Valim to get his input on the design strategy behind to_json and as_json and to clarify which one end users should be using.

It is my understanding that as_json is implementation detail and end users (not inside rails) should be using to_json.

as_json should return an object to be represented in json. You should always overwrite as_json in your module, but always call to_json.

About the bug, have you tried on Rails master? There was a bug related with the json gem overwriting Rails behavior which was fixed a few days ago. That fixed, for instance, the ArgumentError a few reported above.

I'm glad to reopen if this is still an issue.

Implementing as_json is right. Using to_json is a mess because JSON libraries use it for their internal encoding API.

This is similar to the Marshal library: you implement _dump to return a primitive Ruby object to marshal. You're responsible for returning a marshalable representation of your object, not the action marshaled bytes.

Similarly for JSON: you implement as_json to return a JSON representation of your object. The actual work of building a JSON string is handled by internal methods.

This is a clearer, cleaner separation of responsibility than using a single to_json method for both providing JSON representations and for building JSON strings.

So yes, this is a bug :)

Reviewing the examples above, this was fixed. Please verify on latest master!

As JK assigned, if someone wants to backport the fix from master to 2-3-stable, a patch is welcome. The original commit is:

http://github.com/rails/rails/commit/7bd85a8fc2d216a5e2b1d0380df572...

Mr. Valim,

Looks like the patch you provided is not working for me in rails3. Here is the breakdown.

ActiveRecord::Schema.define(:version => 20100630160235) do

  create_table "users", :force => true do |t|
    t.string   "name"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

end

class User < ActiveRecord::Base
end

class UsersController < ApplicationController
  def index
    User.delete_all
    User.create(:name => 'John')
    User.create(:name => 'Mary')
    @users = User.all

    respond_to do |format|
      format.html # index.html.erb
      format.xml  { render :xml => @users }
      format.json  { render :json => @users.as_json(:only => :name) }
    end
  end
end

format.json  { render :json => @users.as_json(:only => :name) }
[{"user":{"name":"John","created_at":"2010-06-30T16:07:42Z","updated_at":"2010-06-30T16:07:42Z","id":9}},{"user":{"name":"Mary","created_at":"2010-06-30T16:07:42Z","updated_at":"2010-06-30T16:07:42Z","id":10}}]

#If I change to to_json from as_json then it is working great

format.json  { render :json => @users.to_json(:only => :name) }
[{"user":{"name":"John"}},{"user":{"name":"Mary"}}]

# once again note that I conducted this test on rails edge and it is failing

• installed latest json gem
• Successfully installed json-1.4.3
• if I use @users.to_json(:only => :name) then every thing works fine.

Whether to use to_json or as_json is little confusing. As JK and JV mentioned above, as_json is means to get to right to_json output. as_json should be used in the model to change the behavior of the model when to_json is invoke.

by invoking @users.as_json(), to_json will NEVER get invoked and that is wrong.

I am closing this issue. If there is any question please feel free to post.

I do believe that there should be a rails guide/blog about when to use as_json and when to use to_json.

I am having problems with associations. They do not seem to honor either the to_json or the as_json methods within the child models.

ActiveRecord::Schema.define(:version => 20100713002653) do

  create_table "boos", :force => true do |t|
    t.string   "name"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

  create_table "foos", :force => true do |t|
    t.string   "name"
    t.integer  "boo_id"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

end
class Boo < ActiveRecord::Base
  has_many :foos
end
class Foo < ActiveRecord::Base
  belongs_to :boo

  def as_json(option = {})
    super({ :only => [ :name ] } )
  end
end
class BoosController < ApplicationController
  def index
    b1 = Boo.create(:name => "Tom");
    b1.foos.create(:name => "Alice");
    b1.foos.create(:name => "Jane");
    b2 = Boo.create(:name => "George");
    b2.foos.create(:name => "Suzy");
    b2.foos.create(:name => "Jenny");
    render :json => Boo.find(:all).to_json({ :include => [ :foos ] })
  end
end

curl localhost:3000/boos.json
[{"boo":{"created_at":"2010-07-13T00:52:35Z","id":1,"name":"Tom","updated_at":"2010-07-13T00:52:35Z","foos":[{"boo_id":1,"created_at":"2010-07-13T00:52:35Z","id":1,"name":"Alice","updated_at":"2010-07-13T00:52:35Z"},{"boo_id":1,"created_at":"2010-07-13T00:52:35Z","id":2,"name":"Jane","updated_at":"2010-07-13T00:52:35Z"}]}},{"boo":{"created_at":"2010-07-13T00:52:35Z","id":2,"name":"George","updated_at":"2010-07-13T00:52:35Z","foos":[{"boo_id":2,"created_at":"2010-07-13T00:52:35Z","id":3,"name":"Suzy","updated_at":"2010-07-13T00:52:35Z"},{"boo_id":2,"created_at":"2010-07-13T00:52:35Z","id":4,"name":"Jenny","updated_at":"2010-07-13T00:52:35Z"}]}}]

I would expect all the foos to have only the names.
I also don't understand why the as_json only takes :only and :except. How am I suppose to include associations from a controller if to_json is not suppose to be used?

(I'm using Rails 2.3.5)

@pedz Attached is a patch that fixes the issue that you mentioned. Please try it and let us know if it works for you.

Neeraj, the test in your patch was supposed to be calling super(:only => :size), no? I don't think the following is/should be supported:

def as_json
  { :only => :size }
end

I don't even think as_json should consider such options as :only and :except. Or you either do it manually:

def as_json
  super.slice("only")
end

Or you overwrite to_json to change how to encode it (the representation in as_json is still the same):

def to_json
  super(:only => :size)
end

Attached is a failing test case.

#5374 as_json should return a hash for ActiveModel/ActiveRecord objects

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