Rails: :save returns NoMethodError - ruby-on-rails

Question

I am programming a small rails api for practice. The goal is to POST some data and then save it (after further processing) in a database. The object is being created successfuly. On the save method appears an error which I cannot explain:
NoMethodError (undefined method `[]' for nil:NilClass): app/controllers/api/v1/calculations_controller.rb:19:in `create'
It appears in the :create method (on POST):
# POST /calculations
def create
#calculation = Calculation.new(calculation_params)
if #calculation.save # <- This is line 19
render json: #calculation, status: :created, location: #calculation
else
render json: #calculation.errors, status: :unprocessable_entity
end
end
The model looks like this:
require 'digest'
class Calculation < ApplicationRecord
attr_reader :value, :hash_value, :algorithm, :timestamp
##known_algorithms = ['SHA2_256', 'SHA2_384', 'SHA2_512']
def initialize (params)
#value = params[:value]
#algorithm = params[:algorithm]
validate!
#hash_value, #timestamp = digest
end
private
def digest
case #algorithm
when 'SHA2_256'
result = Digest::SHA2.hexdigest(#value)
when 'SHA2_384'
result = Digest::SHA2.new(384).hexdigest(#value)
when 'SHA2_512'
result = Digest::SHA2.new(512).hexdigest(#value)
end
return result, DateTime.now
end
def validate!
raise ArgumentError.new('Value cannot be empty or NIL!') if #value.nil? or #value.empty?
raise ArgumentError.new('Unknown hashing algorithm!') unless ##known_algorithms.include? #algorithm
end
end
Why does the NoMethodError appear? Did I override some important part in the model class?
Full stack trace as requested:
/home/pbz/.gem/ruby/2.5.0/gems/activerecord-5.2.2/lib/active_record/transactions.rb:424:in `clear_transaction_record_state'
/home/pbz/.gem/ruby/2.5.0/gems/activerecord-5.2.2/lib/active_record/transactions.rb:330:in `ensure in rollback_active_record_state!'
/home/pbz/.gem/ruby/2.5.0/gems/activerecord-5.2.2/lib/active_record/transactions.rb:330:in `rollback_active_record_state!'
/home/pbz/.gem/ruby/2.5.0/gems/activerecord-5.2.2/lib/active_record/transactions.rb:309:in `save'
/home/pbz/.gem/ruby/2.5.0/gems/activerecord-5.2.2/lib/active_record/suppressor.rb:44:in `save'
/home/pbz/RubymineProjects/hasher_api/app/controllers/api/v1/calculations_controller.rb:20:in `create'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal/basic_implicit_render.rb:6:in `send_action'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/abstract_controller/base.rb:194:in `process_action'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal/rendering.rb:30:in `process_action'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/abstract_controller/callbacks.rb:42:in `block in process_action'
/home/pbz/.gem/ruby/2.5.0/gems/activesupport-5.2.2/lib/active_support/callbacks.rb:132:in `run_callbacks'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/abstract_controller/callbacks.rb:41:in `process_action'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal/rescue.rb:22:in `process_action'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal/instrumentation.rb:34:in `block in process_action'
/home/pbz/.gem/ruby/2.5.0/gems/activesupport-5.2.2/lib/active_support/notifications.rb:168:in `block in instrument'
/home/pbz/.gem/ruby/2.5.0/gems/activesupport-5.2.2/lib/active_support/notifications/instrumenter.rb:23:in `instrument'
/home/pbz/.gem/ruby/2.5.0/gems/activesupport-5.2.2/lib/active_support/notifications.rb:168:in `instrument'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal/instrumentation.rb:32:in `process_action'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal/params_wrapper.rb:256:in `process_action'
/home/pbz/.gem/ruby/2.5.0/gems/activerecord-5.2.2/lib/active_record/railties/controller_runtime.rb:24:in `process_action'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/abstract_controller/base.rb:134:in `process'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal.rb:191:in `dispatch'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_controller/metal.rb:252:in `dispatch'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/routing/route_set.rb:52:in `dispatch'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/routing/route_set.rb:34:in `serve'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/journey/router.rb:52:in `block in serve'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/journey/router.rb:35:in `each'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/journey/router.rb:35:in `serve'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/routing/route_set.rb:840:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/rack-2.0.6/lib/rack/etag.rb:25:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/rack-2.0.6/lib/rack/conditional_get.rb:38:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/rack-2.0.6/lib/rack/head.rb:12:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/activerecord-5.2.2/lib/active_record/migration.rb:559:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
/home/pbz/.gem/ruby/2.5.0/gems/activesupport-5.2.2/lib/active_support/callbacks.rb:98:in `run_callbacks'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/callbacks.rb:26:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/executor.rb:14:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/debug_exceptions.rb:61:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/show_exceptions.rb:33:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/railties-5.2.2/lib/rails/rack/logger.rb:38:in `call_app'
/home/pbz/.gem/ruby/2.5.0/gems/railties-5.2.2/lib/rails/rack/logger.rb:26:in `block in call'
/home/pbz/.gem/ruby/2.5.0/gems/activesupport-5.2.2/lib/active_support/tagged_logging.rb:71:in `block in tagged'
/home/pbz/.gem/ruby/2.5.0/gems/activesupport-5.2.2/lib/active_support/tagged_logging.rb:28:in `tagged'
/home/pbz/.gem/ruby/2.5.0/gems/activesupport-5.2.2/lib/active_support/tagged_logging.rb:71:in `tagged'
/home/pbz/.gem/ruby/2.5.0/gems/railties-5.2.2/lib/rails/rack/logger.rb:26:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/remote_ip.rb:81:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/request_id.rb:27:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/rack-2.0.6/lib/rack/runtime.rb:22:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/activesupport-5.2.2/lib/active_support/cache/strategy/local_cache_middleware.rb:29:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/executor.rb:14:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/actionpack-5.2.2/lib/action_dispatch/middleware/static.rb:127:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/rack-2.0.6/lib/rack/sendfile.rb:111:in `call'
/home/pbz/.gem/ruby/2.5.0/gems/railties-5.2.2/lib/rails/engine.rb:524:in `call'
/home/pbz/.rbenv/versions/2.5.3/lib/ruby/gems/2.5.0/gems/puma-3.12.0/lib/puma/configuration.rb:225:in `call'
/home/pbz/.rbenv/versions/2.5.3/lib/ruby/gems/2.5.0/gems/puma-3.12.0/lib/puma/server.rb:658:in `handle_request'
/home/pbz/.rbenv/versions/2.5.3/lib/ruby/gems/2.5.0/gems/puma-3.12.0/lib/puma/server.rb:472:in `process_client'
/home/pbz/.rbenv/versions/2.5.3/lib/ruby/gems/2.5.0/gems/puma-3.12.0/lib/puma/server.rb:332:in `block in run'
/home/pbz/.rbenv/versions/2.5.3/lib/ruby/gems/2.5.0/gems/puma-3.12.0/lib/puma/thread_pool.rb:133:in `block in spawn_thread'

Answer 1

Don't override initialize in the AR. It could possibly break a lot of stuff in your models.
You can use after_initialize.
The after_initialize callback will be called whenever an Active Record
object is instantiated, either by directly using new or when a record
is loaded from the database. It can be useful to avoid the need to
directly override your Active Record initialize method.
def after_initialize
# Gets called right after Calculation.new
# Do some stuff here
end
If you still want to use initialize you must do something like this:
def initialize(attributes = {})
super
self.attributes = attributes
end

Answer 2

I did find out (thanks to #Зелёный), that to create values for the model after creating it (new) I need to use the after_initialize callback Rails provides. Together with this comment on how to access model instance variables, I was able to achieve the functionality I wanted.
The original NoMethodError was a result of my incorrect use of the initialize method. The following code is the final result, which works with the default controller.
require 'digest'
class Calculation < ApplicationRecord
##known_algorithms = ['SHA2_256', 'SHA2_384', 'SHA2_512']
after_initialize :init
private
def init
validate!
calculate!
end
def calculate!
self.hash_value, self.timestamp = digest
end
def digest
case algorithm
when 'SHA2_256'
result = Digest::SHA2.hexdigest(value)
when 'SHA2_384'
result = Digest::SHA2.new(384).hexdigest(value)
when 'SHA2_512'
result = Digest::SHA2.new(512).hexdigest(value)
end
return result, DateTime.now
end
def validate!
raise ArgumentError.new('Value cannot be empty or NIL!') if value.nil? or value.empty?
raise ArgumentError.new('Unknown hashing algorithm!') unless ##known_algorithms.include? algorithm
end
end