Oj: How can I be sure OJ 3.x is working with Active Model Serializers (render json)?

[hhff]

I remember on an old 2.x version of OJ, I had to do

module ActiveSupport::JSON::Encoding
 class Oj < JSONGemEncoder
   def encode value
     ::Oj.dump(value.as_json, options.dup)
   end
 end
end

ActiveSupport.json_encoder = ActiveSupport::JSON::Encoding::Oj

Oj.default_options = { mode: :compat }

To get OJ working with ActiveModel::Serializers (as the AMS gem simply hooks into render json: User.first).

In 3.0 - is this still something I need to do? I've added the Oj.optimize_rails() call to an initializer, but after binding into the OJ Gem i'm not seeing anything catch when running my test suite.

Happy to add something to the Rails readme once I figure this out!

[ohler55]

Just calling Oj.optimize_rails should be enough. What makes you think it is not working? Have you done a trace?

[hhff]

Yes - I ran a trace (against an endpoint that uses AMS) - I can't see any calls to the Oj Gem. I'm seeing:

#0:/Users/hhff/.rvm/gems/ruby-2.3.1/gems/active_model_serializers-0.10.6/lib/active_model_serializers/serializable_resource.rb:36:ActiveModelSerializers::SerializableResource:<:     end

#0:/Users/hhff/.rvm/gems/ruby-2.3.1/gems/activesupport-5.1.1/lib/active_support/core_ext/object/json.rb:33:ActiveSupport::ToJsonWithActiveSupportEncoder:>:     def to_json(options = nil)

But no mention of OJ. (Thankyou for this great Gem BTW!)

[ohler55]

Glad you like it. Looks like I'll have to dig into the ActiveSupport code and figure out what has changed.

[ohler55]

Can you give me a longer trace. That would help me figure out where to look.

[ohler55]

Even better would be a simple test case and I'll trace it through ActiveSupport.

[hhff]

On it!

On Fri, Sep 1, 2017 at 11:27 AM Peter Ohler [e-mail]
wrote:

Even better would be a simple test case and I'll trace it through
ActiveSupport.

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[ohler55]

Thanks. We will get to the bottom of this and then update the docs.

[hhff]

Hi @ohler55 !

You can clone a repro here: https://github.com/hhff/tracerr

This is just a vanilla Rails 5.1.2 app with a single resource, serializer & test. Commits should explain the additions to the rails boilerplate: https://github.com/hhff/tracerr/commits/master

bin/rails db:migrate RAILS_ENV=test
rake test

And you should see a trace in your console. Searching oj in stack trace won't yield anything from the OJ gem, but you should see calls to active_model_serializers. Lemme know if this helps!

[ohler55]

Still looking but I have a theory. So I put in a puts in active_support/json/encoding.rb. It shows self.encode is called and that the Encoding.json_encoder is Oj::Rails::Encoder which is correct. I'm guessing that the trace stops there because it drops into the C extension. Will add a print to Oj in C and see if it shows up.

[hhff]

Ok! Sounds promising!

On Fri, Sep 1, 2017 at 1:10 PM Peter Ohler [e-mail] wrote:

Still looking but I have a theory. So I put in a puts in
active_support/json/encoding.rb. It shows self.encode is called and that
the Encoding.json_encoder is Oj::Rails::Encoder which is correct. I'm
guessing that the trace stops there because it drops into the C extension.
Will add a print to Oj in C and see if it shows up.

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[ohler55]

Oj is being called. Now how can this be confirmed is another story. Maybe a flag is needed to trace or at least indicate that Oj was called. Let me think about that.

[hhff]

That would be great! It's almost too magic and I think most implementers will get an uneasy feeling (like I did) a spend a few hours trying to prove that it's in place!

Thankyou @ohler55 !

[ohler55]

A follow up, Oj is being called and I am surprises the trace does not show entering a C call. Seems like a bug in the tracer. Once in the Oj encode function Oj does check to see if the object is a special one or if the to_json call should be made. It looks like the to_json is being called on some part of the object if not the object itself. Once I add some tracing that should show up as well. Armed with that info a few more classes can be added to the optimized list for some performance gains.

[ohler55]

Here is the trick!

Tracer.display_c_call = true

I think that is all that is needed. That and an update to the Rails.md file.