How to use conditional attributes with jsonapi-serializers

I am working on a Ruby on Rails project with ruby-2.5.0 and Rails 5. i am working on api part, i have used jsonapi-serializers gem in my app. I want to add conditional attribute in serializer.

Controller:

class RolesController < ApplicationController
  def index
    roles = Role.where(application_id: @app_id)
    render json: JSONAPI::Serializer.serialize(roles, is_collection: true)
  end
end

Serializer:

class RoleSerializer
  include JSONAPI::Serializer

  TYPE = 'role'

  attribute :id
  attribute :name
  attribute :application_id

  attribute :application do
    JSONAPI::Serializer.serialize(object.application)
  end
end

Here application is a model which has_many roles and roles belongs to application. I want to add application details in some conditions. I also tried like:

Controller:

    class RolesController < ApplicationController
      def index
        roles = Role.where(application_id: @app_id)
        render json: JSONAPI::Serializer.serialize(roles, is_collection: true, params: params)
      end
    end

Serializer:

class RoleSerializer
  include JSONAPI::Serializer

  TYPE = 'role'

  attribute :id
  attribute :name
  attribute :application_id

  attribute :application do
    JSONAPI::Serializer.serialize(object.application), if: @instance_options[:application] == true
  end
end

But @instance_options is nil. Please help me how i can fix it. Thanks in advance.

In the jsonapi-serializers this is what is said about custom attributes: 'The block is evaluated within the serializer instance, so it has access to the object and context instance variables.'

So, in your controller you should use:

render json: JSONAPI::Serializer.serialize(roles, is_collection: true, context: { application: true })

And in your serializer you should use context[:application] instead of @instance_options