Using sparse fieldsets in ActiveModelSerializers

sparse_fieldsets.rb

class BaseApiController
  def render_json_api(options)
    render(
      options.merge(included).merge(fields: fields).merge(adapter: :json_api)
    )
  end

  # Allows limiting fields in given resource type's payloads.
  # `fields` param is sent as a hash in which:
  # - keys are singular or plural resource names (e.g. `accounts` or `account`)
  # - values are attribute names in snake or camel case.
  #   Can be either sent as array:
  #   `fields[accounts][]=name&fields[accounts][]=search_interval`
  #   or divided by commas: `fields[accounts]=name,searchInterval`
  #
  # Examples of valid request:
  # - /accounts/1?fields[account]=name,search_interval&fields[custom_feeds]=notifications&include[]=custom_feeds
  # - /accounts/1?fields[account][]=searchInterval&fields[account][]=name&fields[custom_feeds][]=notifications&include[]=custom_feeds
  #
  # More info: https://jsonapi.org/format/#fetching-sparse-fieldsets
  def fields
    result = params.permit(fields: {})[:fields]
    return unless result.respond_to?(:to_h)

    result.to_h.map do |k, v|
      v = v.split(",") if v.is_a?(String)
      [k, v.map(&:underscore)]
    end.to_h
  end

  def included
    params.permit(include: []).to_h.symbolize_keys
  end
end