Serialize Object/Array when no AMS Serializer is defined

[kayakyakr]

I'm receiving an issue, in latest master, where I receive NoMethodError (undefined method new' on nil:NilClass.)` when I attempt to serialize something like, ['Result is invalid'].

From everything I can tell, it's rolling through the get_serializer_for method, failing to find a serializer for my object, but trying to create an instance of that serializer anyway. It should fall back to a default serializer.

Sorry if this has been addressed, I checked through the issues but didn't see anything that stood out to me. As a workaround, I'm having to specify "render json: obj, adapter: false" when I want to render a json-ready hash rather than a rails model.

[bf4]

Needs more info. What is obj? Which ref are you on? (paste output of bundle show active_model_serializers) Which Ruby? Which Rails? What does your serializer look like? Could you provide some more of the stack trace?

[kayakyakr]

active_model_serializers-7b0a85fdda85
rbx 2.2.10
rails 4.1

code is called as:

render json: {error: 'Result is Invalid'}
# throws exception because serializer is nil

Stack trace is less than interesting and I don't currently have an example set up to cause the error, but digging through the code:

#action_controller/serialization.rb:23
@_serializer ||= ActiveModel::Serializer.serializer_for(resource) # @_serializer is nil when a serializer for the resource is not explicitly defined.

#action_controller/serialization.rb:47
object = serializer.new(resource, @_serializer_opts) # calls new on serializer when it may be nil

Is render json: {} supposed to fall back to a more appropriate renderer?

[bf4]

perfect. So, the bug is there's no serializer for Hash. solutions: call `to_json` on your hash, and the resulting string will be your response body :)

[kayakyakr]

I like my adapter: false workaround.

-- edited because it came across assholish, when I didn't mean it to be.

[bf4]

I suppose we could argue this is a bug in AMS in that if it can't find a serializer for non-string object, it should either just pass it through untouched or call to_json on it depending on the context, since that is what the renderer does it non-string, eventually.

[kayakyakr]

That would be the best, I think.

I also noticed that if you pass it a model that you haven't built a serializer for (yet or at all), it fails in the same way. Previous versions of AMS either passed those objects on to a lower renderer or just called to_json on them. Also chokes in the same way with an association without a serializer.

[bf4]

Yeah, wanna pair on a PR to pass through if adapter is nil or serializer is nil?

[kayakyakr]

I need to do some more digging. It looks like it should be passing it to super as soon as serializer comes back nil, which means something else is going on.

[bf4]

I think you have it on the nose, if I understand what you understand. tl;dr

def _render_with_renderer_json(resource, options)
  if use_adapter? && (serializer = get_serializer(resource))
    # adapter ~ Adapter.create(serializer.new(resource))
     super(adapter, options)
  else
    super(resource, options)
  end
end

• where use_adapter? is true either when :adapter is not given or when it's given and falsy
• where get_serializer(resource) returns a serializer class either when :serializer is given or when it can be inferred by ActiveModel::Serializer.serializer_for(resource)
• thus, the AMS adapter is used when the adapter is given or inferred AND the serializer is given or inferred.

So, it's surprising that render json: {error: 'Result is Invalid'} would hit object = serializer.new(resource, @_serializer_opts) since though use_adapter? is true, get_serializer should be returning nil

[kayakyakr]

Yeah, that's what is confusing me. Let cause this error to occur and see what happens.

[bf4]

So, that's an easy test to write, no?

def render_object_without_serializer
  render json: {error: 'Result is Invalid'}
end
def test_render_object_without_serializer
  get :render_object_without_serializer
  assert_equals @response.body, '{ "error": "Result is Invalid" }'
end

[kayakyakr]

I got it!

render json: ['errors']

It's because it's wrapped in an array. The error isn't in the rendering code, but instead is here:
active_model_serializers-7b0a85fdda85/lib/active_model/serializer/array_serializer.rb:17:in initialize'`

    def initialize(objects, options = {})
        options.merge!(root: nil)

        @objects = objects.map do |object|
          serializer_class = options.fetch(
            :serializer,
            ActiveModel::Serializer.serializer_for(object)
          )
          serializer_class.new(object, options.except(:serializer))
        end
        @meta     = options[:meta]
        @meta_key = options[:meta_key]
      end

So it's the array serializer that needs to know how to handle non-serializer data.

[kayakyakr]

Easier test to write. Much harder thing to fix because array serializer feeds that straight in to the adapter which doesn't know how to handle a non-serializer object or string.

[bf4]

I guess it would need a procy serializer that just calls to_json?

[joaomdmoura]

Hey ppl, just read trough the thread, I'm happy to see that you narrowed that the issue!
Just keep in mind that we are kind starting the fix the has_many at #955
I know that it's probably not related to array_serializer it self but just keep it in mind! 😄

[kayakyakr]

That should fix it @joaomdmoura, or at least indicate how this should be fixed. It's the same issue at the core if it isn't the exact same issue.

[GriffinHeart]

I think this is the same as #772

[kayakyakr]

Yes, it is. Also the same as #955 and #877, or at least should be fixed by the fix for that issue.

[GriffinHeart]

Just to add some info the nil comes from here

https://github.com/rails-api/active_model_serializers/blob/master/lib/active_model/serializer.rb#L243-L247

def self.get_serializer_for(klass)
  serializers_cache.fetch_or_store(klass) do
    serializer_class_name = "#{klass.name}Serializer"
    serializer_class = serializer_class_name.safe_constantize

    if serializer_class
      serializer_class
    elsif klass.superclass
      get_serializer_for(klass.superclass)
    end
  end
end

When using render json: ['errors'] class will be String which has no serialiser, same thing as render json: [{a: 1}] where class will be Hash which also has no serialiser, thus serializer_class is nil

[joaomdmoura]

It was fixed at #962
I'm closing this for now, but would be awesome if you guys could test it yourself 😄

[kayakyakr]

Seems to be working. Had to switch up to using the FlattenJson serializer for some of the parts where I was building up a serializable hash outside of the context of the controller, but that was an unrelated change.

[phuongnd08]

This issue has been re-introduced in 0.10.5. "render [{}]" is returning error.

UncaughtThrowError: uncaught throw :no_serializer

[bf4]

@phuongnd08 You've commented on an issue from over a year ago without sufficient information to debug. I can't think of a realistic scenario where you'd be using AMS and render an array with a hash in it to json. Please open a new issue.