has_ancestry and active model serializers - ruby-on-rails

Question

I have a model Category
class Category < ActiveRecord::Base
attributes :id, :name, :order, :x, :y, :z
has_ancestry
end
In my controller, I can use the following to get the whole tree as JSON
Category.first.subtree.arrange_serializable
But this returns all DB attributes such as created_at or id
I wanted to use the active model serializer to shape my output without losing the tree structure.
class CategorySerializer < ActiveModel::Serializer
# Children is the subtree provided by ancestry
attributes :name, :x, :children
end
Controller
class CategoryController < ActionController::Base
def index
category = Category.first
render :json => category
end
end
The code above will only show the first sub level, but not the children of the children.
Any help appreciated

Answer 1

To use arrangement, we need to pass an additional parameter to serializer, you can do it this way:
category.subtree.arrange_serializable do |parent, children|
CategorySerializer.new(parent, scope: { children: children })
end
And here's how you can take that parameter in serializer:
class CategorySerializer < ActiveModel::Serializer
attributes :id, :name, :order, :children
def children
scope.to_h[:children]
end
end
You may also want to take a look at this test to have a better understanding how arrange_serializable works.

Answer 2

In AMS 10.x (master branch) we can support external parameters in such way:
class CategorySerializer < ActiveModel::Serializer
attributes :id, :name, :order, :children
def children
instance_options[:children]
# or instance_options[:children]&.as_json
end
end
Next you can simply pass children to the serializer:
category.subtree.arrange_serializable do |parent, children|
CategorySerializer.new(parent, children: children)
end
or
category.subtree.arrange_serializable do |parent, children|
ActiveModelSerializers::SerializableResource(parent, children: children)
end