active model serializer has_many association not working

Question

I have two associated models, the parent= Activity, and it has_many association to Cost. I do an API call to get activity detail which uses a serializer, and also wanted to add Cost serialized as well. So inside the ActivitySerializer I have tried this:

Class ActivitySerializer: < ActiveModel::Serializer


ActiveModel::Serializer.config.key_transform = :unaltered




attributes :id, 
          :name, 
          :description
 ...
has_many costs, each_serializer: CostSerializer
end

The CostSerializer looks like this:

class CostSerializer < ActiveModel::Serializer

ActiveModel::Serializer.config.key_transform = :unaltered

attributes  :id, 
          :amount, 
          :description
end

The result is that Activity data looks good but Cost data give me this:

relationships":{"costs":{"data":[{"id":"20","type":"costs"}]}

Not sure why amount and description get dropped off. If I do this, it works (add listCosts to attributes in ActivitySerializer):

def listCosts
  object.costs.map do |cost|
    CostSerializer.new(cost, scope:scope, root: false, event: object)
  end
end 

The output is a bit different, doesn't have Relationship, but does have the serializer attributes that I want. I am using Rails 5.1.3 with AMS 0.10.

Answer 1

I'm assuming you're using the json_api adapter. As per the sample for the JSON API specification in http://jsonapi.org/examples/, any other attribute other than the "type" and "id" of the associated model can be exposed through the "included" property. You may checkout the discussion in https://github.com/rails-api/active_model_serializers/issues/1056