JSON adapter with empty array does not maintain root key

[meltingice]

If you attempt to serialize an empty array with the JSON adapter and ArraySerializer, the root key becomes an empty string. This issue is present in 0.10.0.rc2 and the latest master branch commit at this time (17c353826056bc3eac3e6d6a2fd081af175bb6ad).

Example Code

class Api::V1::ArticlesController < Api::V1::BaseController
  def index
    @articles = []
    render json: @articles, each_serializer: Api::V1::ArticleSerializer
  end
end

Expected

{
  "articles": []
}

Actual

{
  "": []
}

[beauby]

Thing is, when you have an empty array, there is no real way for AMS to infer the type of resources you would have had in it (at least not based on the resources themselves since, well there aren't any). Two possible workarounds:

• explicitly specify the root option
• make a custom collection serializer that inherits from ArraySerializer that sets the root for you.

[NullVoxPopuli]

AMS could attempt to safe_constantize the model part of {model}Serializer and derive the root key from that?

[meltingice]

From a design standpoint, is there ever really an instance where you wouldn't have an array of homogenous object types? At least, for the JSON adapter? I don't see why AMS couldn't deduce the root key based on the serializer. The workarounds are fine, but it was definitely a surprise to me how it reacted in this instance. Doesn't seem like a good expected result.

Ryan LeFevre (@meltingice)
HODINKEE, Inc.
Sr. Software Engineer

_____________________________

From: Lucas Hosseini notifications@github.com
Sent: Tuesday, September 15, 2015 5:45 PM
Subject: Re: [active_model_serializers] JSON adapter with empty array does not maintain root key (#1153)
To: rails-api/active_model_serializers active_model_serializers@noreply.github.com
Cc: Ryan LeFevre meltingice8917@gmail.com

Thing is, when you have an empty array, there is no real way for AMS to infer the type of resources you would have had in it (at least not based on the resources themselves since, well there aren't any). Two possible workarounds: explicitly specify the root option make a custom collection serializer that inherits from ArraySerializer that sets the root for you.

—
Reply to this email directly or view it on GitHub.

[NullVoxPopuli]

@beauby @joaomdmoura how do you feel about inferring the root name in this scenario? Can you think of any down sides?

[beauby]

I think we should do it but only if it cannot be inferred from the resources themselves (mainly because there are none), otherwise it will bring pain when serializing with a custom serializer (like PostPreviewSerializer).

[NullVoxPopuli]

yeah, that's what I was thinking.

[NullVoxPopuli]

Imma get a PR for this

[NullVoxPopuli]

Addressed in #1156

[bf4]

@meltingice are we discussing Array.new or Article.none?

If Array.new, AMS does nothing to resources that have no serializer, and there's no serializer for the Array primitive (0.10.0 master, 0.10.0.rc2, 0.9.3, 0.8.3.

The option for manually specifying the serializer is serializer, not each_serializer. Naming 💥 As I commented there:

# Get serializer either explicitly :serializer or implicitly from resource
# Remove :serializer key from serializer_opts
# Replace :serializer key with :each_serializer if present

Without serializer, it couldn't know the name of the instance variable. The best it could do would be given no serializer is found for the argument to json in the controller,

class ArticleController < ApplicationController
  def index
   @articles = []
    render json: @articles, adapter: :json #=> { articles: [] }, where the resource root comes from the current controller.
  end
end

If Article.none (an empty collection), then it could find the serializer implicitly.

[meltingice]

Sorry, thought I replied to this, but must have forgotten to send the email. In this case it actually is Array.new because I'm not serializing an ActiveRecord::Relation.

[aserafin]

I've noticed it also doesn't respect the root: false option when we return empty array