fix: allow using active_model_serializers in associations (compat)

lib/oj_serializers/compat.rb

@@ -14,6 +14,38 @@ def self.one(object, options = nil)
   def self.many(array, options = nil)
     array.map { |object| new(object, options) }
   end
+
+  # OjSerializer: Used internally to write a single object association in :hash mode.
+  #
+  # Returns nothing.
+  def self.one_as_hash(object)
+    new(object)
+  end
+
+  # OjSerializer: Used internally to write an association in :hash mode.
+  #
+  # Returns nothing.
+  def self.many_as_hash(array)
+    array.map { |object| new(object) }
+  end
+
+  # OjSerializer: Used internally to write a single object association in :json mode.
+  #
+  # Returns nothing.
+  def self.write_one(writer, object, options)
+    writer.push_value(new(object, options))
+  end
+
+  # OjSerializer: Used internally to write an association in :json mode.
+  #
+  # Returns nothing.
+  def self.write_many(writer, array, options)
+    writer.push_array
+    array.each do |object|
+      write_one(writer, object, options)
+    end
+    writer.pop
+  end
 end
 
 require 'oj_serializers'

spec/oj_serializers/compat_spec.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+require 'support/models/album'
+require 'support/serializers/active_model_serializer'
+
+class CompatSerializer < Oj::Serializer
+  has_one :item, serializer: ActiveModelSerializer
+  has_many :items, serializer: ActiveModelSerializer
+end
+
+RSpec.describe "AMS Compat", type: :serializer do
+  def expect_encoded_json(object)
+    expect(Oj.dump(object).tr("\n", ''))
+  end
+
+  it 'can use ams serializer in associations' do
+    album = Album.abraxas.tap { |a| a.id = 1 }
+    object = OpenStruct.new(item: album, items: [album, album])
+    attrs = {id: 1, name: "Abraxas"}
+
+    expect_encoded_json(CompatSerializer.one(object)).to eq({
+      item: attrs,
+      items: [attrs, attrs],
+    }.to_json)
+  end
+end