Deserialize JSON Strings Directly into Models?

I have Ruby models which are populated from the responses of API calls in the following way:

• JSON.parse converts the response to a Hash

• the Hash is passed into the initialize method of a class

• the initialize method converts camelCase hash keys and assigns underscore_case instance variables

• controller code works with these instances and converts back to json to send to the browser

This works fine, but some of these response objects are large. Others are arrays of large objects.

Profiling shows that this process consumes a lot of CPU (and memory, but that is less of a concern) -- which makes sense given that I create hashes in order to create objects, and the back and forth between camelCase and underscore_case happens A LOT -- so what libraries or techniques have you come across which solve this problem?

Here is an oversimplified example:

JSON response from a third party API (unlikely to change):

"{\"abcDef\": 123, \"ghiJkl\": 456, \"mnoPqr\": 789}"

Class definition (attributes unlikely to change):

class Data
  attr_accessor :abc_def, :ghi_jkl, :mno_pqr

  def initialize(attributes = {})
    attributes.each do |key, val|
      send "#{key.underscore}=".to_sym, val
    end
  end

  def as_json
    instance_variables.reduce({}) do |hash, iv|
      iv_name = iv.to_s[1..-1]
      v = send(iv_name) if self.respond_to?(iv_name)
      hash[iv_name.camelize(:lower)] = (v.as_json(options) if v.respond_to?(:as_json)) || v
      hash
    end
  end
end

Controller:

get '/' do
  d = Data.new JSON.parse(api.get)
  # ... do some work ...
  content_type 'application/json'
  d.to_json
end

TheJSON schema and data class attributes are unlikely to change. Consider implementing the class to encapsulate the JSON hash, adapting it to the ruby idioms and whatever other custom operations you've added. This should greatly decrease the cost and complexity of deserialization.

StackExchange Code Review Q#69855, answer score: 2