Oj.generate: don't call as_json on rails model

[yosiat]

Hi,

Since I upgraded to Oj 3.11.4 (from 3.11.2) json serialization of rails models don't work as expected.

# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  # Activate the gem you are reporting the issue against.
  gem "activerecord", "~> 6.1.0"
  gem "sqlite3"
  gem "oj", "3.11.4"
end

require "active_record"
require "minitest/autorun"
require "logger"
require "oj"

Oj.optimize_rails

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")

ActiveRecord::Schema.define do
  create_table :posts, force: true do |t|
    t.string :title
    t.string :body
  end
end

class Post < ActiveRecord::Base
end

post = Post.create!(title: "Hello", body: "World")

puts Oj.generate({ post: post })

With Oj 3.11.2, the output is:

{"post":{"id":1,"title":"Hello","body":"World"}}

And with 3.11.4, the output is:

{"post":"#<Post:0x00007f808b8b30b8>"}

Am I missing configuration step ? or is it a bug?

[ohler55]

Have you tried the most recent Oj? 3.11.4 is 5 months out of date.

[yosiat]

@ohler55 same with 3.13.7, I upgraded from 3.11.2 and did manual bisect to find the version who caused this bug.

[ohler55]

I see, okay will try to identify what changed and if it is different than what active support does. Thanks for the very clear way to reproduce.

[kmasuda-aiming]

https://github.com/ohler55/oj/blob/develop/CHANGELOG.md#3114---2021-04-14

Fixed compatibility issue with Rails and the JSON gem that requires a special case when using JSON.generate versus call to_json on an object.

https://github.com/ohler55/oj/issues/651

Oj.generate now behaves the same as JSON.generate.

If you expect {"post":{"id":1,"title":"Hello","body":"World"}} , Oj.dump({ post: post }) or { post: post }.to_json seems to good to use.

[yosiat]

@kmasuda-aiming thanks! so in some places I will need to use Oj.dump.

I found an issue with Oj.dump, same reproduction script (I posted on issue body) with oj 3.13.8

and added those lines:

post_obj = { post: post }

puts Oj.generate(post_obj)
puts post_obj.to_json
puts Oj.dump(post_obj)

And Oj.dump fails (Oj.generate and .to_json are working) -

Traceback (most recent call last):
        1: from oj_bug.rb:42:in `<main>'
oj_bug.rb:42:in `dump': Too deeply nested. (NoMemoryError)

If I put mode: :rails in Oj.dump call - it works.

Any idea why?

[ohler55]

Without knowing what the active record layout is I would guess there is an object that implements #as_json by returning itself instead of a Hash or in some cases I have seen it actually calls generate in the #as_json. In rails mode Oj takes some additional steps to catch that. The other modes don't bother as according to the docs #as_json always returns a Hash. Oddly enough active support started the use of #as_json and so far that is the only gem I have seen violate their own documentation.

[kmasuda-aiming]

I'm sorry I gave you the wrong information.

In the case of mode: :object, it generates a string like the blew.

{"^o":"Post","new_record":false,"attributes":{"^o":"ActiveModel::AttributeSet","attributes":{"id":{"^o":"ActiveModel::Attribute::FromDatabase","name":"id","value_before_type_cast":1,"type":{"^o":"ActiveRecord::ConnectionAdapters::SQLite3Adapter::SQLite3Integer","precision":null,"scale":null,"limit":null,"range":{"^u":["Range",-9223372036854775808,9223372036854775808,true]}},"original_attribute":null,"value":1},"title":{"^o":"ActiveModel::Attribute::FromDatabase","name":"title","value_before_type_cast":"Hello","type":{"^o":"ActiveModel::Type::String","true":"t","false":"f","precision":null,"scale":null,"limit":null},"original_attribute":null,"value":"Hello"},"body":{"^o":"ActiveModel::Attribute::FromDatabase","name":"body","value_before_type_cast":"World","type":{"^o":"ActiveModel::Type::String","true":"t","false":"f","precision":null,"scale":null,"limit":null},"original_attribute":null,"value":"World"}}},"association_cache":{},"primary_key":"id","readonly":false,"previously_new_record":true,"destroyed":false

mode: :json ( same as mode: :compat ) or mode: :rails generates {"post":{"id":1,"title":"Hello","body":"World"}}.

Oj.dump(post_obj, mode: :rails) to change the mode. If you want to change the settings for the whole system, you can use Oj.default_options = { mode: :rails } .

[ohler55]

I think this issue can be closed. Any objections?