undefined method `keys' for nil:NilClass when calling gem method - ruby-on-rails

Question

I am trying to call a method from a gem that I have created but keep getting the error stated in the title. I've looked into the error but still dont know why it is occurring. When I run the file in the Command prompt it works perfectly. All I want to do it populate the method with user input and display the result in my index page. I am running the following it the command prompt:
irb -rubygems
require 'unit_converter'
UnitConverter::Weight.new.conversions(1, :kg)
The output changes depending on what I type in but for example the output for this would be:
["2.20462pounds", "0.157473stone"]
It's only when I try and link it up to my erb file that i get the error mentioned.
To reproduce the error This is the method I am creating in my measurements_controller file:
def unit_converter
#input1 = params[:value]
#input2 = params[:unit]
#result = UnitConverter::Weight.new.conversions(#input1.to_i , #input2)
end
And in my index.html.erb file I have a form like so:
<%= form_tag "/validate" do %>
<%= text_field_tag :value %>
<%= text_field_tag :unit %>
<%= submit_tag "Search" %>
<% end %>
<%= #result %>
And these are my routes to link everything up
get '/check', :controller=>'measurements', :action=>'index'
post '/validate', :controller=>'measurements', :action=>'unit_converter'
This is the gem that I am using and conversions is the method:
module UnitConverter
class ConversionError < StandardError
end
class Weight
# lookup table
CONVERSIONS = {
kg: {
pounds: 2.20462,
stone: 0.157473,
},
pounds: {
kg: 0.453592,
stone: 0.0714286
},
stone: {
kg: 6.35029,
pounds: 14
}
}
def convert(value, from, to:)
raise ConversionError, "Value is not numeric" unless value.is_a? Numeric
raise ConversionError, "Value #{value} is not positive" unless value >= 0
"#{value * conversion_ratio(from, to) }#{to.to_s}"
end
def conversions(value, unit)
CONVERSIONS[unit].keys.map do |other_unit|
convert(value, unit, to: other_unit)
end
end
private
def conversion_ratio(from, to)
begin
CONVERSIONS.fetch(from).fetch(to)
rescue KeyError
raise ConversionError, "Cannot convert #{from.to_s} to #{to.to_s}"
end
end
end
end
My full stack trace:
**unit_converter (0.0.0) lib/unit_converter.rb:32:in `conversions'
app/controllers/measurements_controller.rb:9:in `unit_converter'
actionpack (6.0.2.1) lib/action_controller/metal/basic_implicit_render.rb:6:in `send_action'
actionpack (6.0.2.1) lib/abstract_controller/base.rb:196:in `process_action'
actionpack (6.0.2.1) lib/action_controller/metal/rendering.rb:30:in `process_action'
actionpack (6.0.2.1) lib/abstract_controller/callbacks.rb:42:in `block in process_action'
activesupport (6.0.2.1) lib/active_support/callbacks.rb:135:in `run_callbacks'
actionpack (6.0.2.1) lib/abstract_controller/callbacks.rb:41:in `process_action'
actionpack (6.0.2.1) lib/action_controller/metal/rescue.rb:22:in `process_action'
actionpack (6.0.2.1) lib/action_controller/metal/instrumentation.rb:33:in `block in process_action'
activesupport (6.0.2.1) lib/active_support/notifications.rb:180:in `block in instrument'
activesupport (6.0.2.1) lib/active_support/notifications/instrumenter.rb:24:in `instrument'
activesupport (6.0.2.1) lib/active_support/notifications.rb:180:in `instrument'
actionpack (6.0.2.1) lib/action_controller/metal/instrumentation.rb:32:in `process_action'
actionpack (6.0.2.1) lib/action_controller/metal/params_wrapper.rb:245:in `process_action'
activerecord (6.0.2.1) lib/active_record/railties/controller_runtime.rb:27:in `process_action'
actionpack (6.0.2.1) lib/abstract_controller/base.rb:136:in `process'
actionview (6.0.2.1) lib/action_view/rendering.rb:39:in `process'
actionpack (6.0.2.1) lib/action_controller/metal.rb:191:in `dispatch'
actionpack (6.0.2.1) lib/action_controller/metal.rb:252:in `dispatch'
actionpack (6.0.2.1) lib/action_dispatch/routing/route_set.rb:51:in `dispatch'
actionpack (6.0.2.1) lib/action_dispatch/routing/route_set.rb:33:in `serve'
actionpack (6.0.2.1) lib/action_dispatch/journey/router.rb:49:in `block in serve'
actionpack (6.0.2.1) lib/action_dispatch/journey/router.rb:32:in `each'
actionpack (6.0.2.1) lib/action_dispatch/journey/router.rb:32:in `serve'
actionpack (6.0.2.1) lib/action_dispatch/routing/route_set.rb:837:in `call'
rack-pjax (1.1.0) lib/rack/pjax.rb:12:in `call'
remotipart (1.4.4) lib/remotipart/middleware.rb:32:in `call'
warden (1.2.8) lib/warden/manager.rb:36:in `block in call'
warden (1.2.8) lib/warden/manager.rb:34:in `catch'
warden (1.2.8) lib/warden/manager.rb:34:in `call'
rack (2.2.2) lib/rack/tempfile_reaper.rb:15:in `call'
rack (2.2.2) lib/rack/etag.rb:27:in `call'
rack (2.2.2) lib/rack/conditional_get.rb:40:in `call'
rack (2.2.2) lib/rack/head.rb:12:in `call'
actionpack (6.0.2.1) lib/action_dispatch/http/content_security_policy.rb:18:in `call'
rack (2.2.2) lib/rack/session/abstract/id.rb:266:in `context'
rack (2.2.2) lib/rack/session/abstract/id.rb:260:in `call'
actionpack (6.0.2.1) lib/action_dispatch/middleware/cookies.rb:648:in `call'
activerecord (6.0.2.1) lib/active_record/migration.rb:567:in `call'
actionpack (6.0.2.1) lib/action_dispatch/middleware/callbacks.rb:27:in `block in call'
activesupport (6.0.2.1) lib/active_support/callbacks.rb:101:in `run_callbacks'
actionpack (6.0.2.1) lib/action_dispatch/middleware/callbacks.rb:26:in `call'
actionpack (6.0.2.1) lib/action_dispatch/middleware/executor.rb:14:in `call'
actionpack (6.0.2.1) lib/action_dispatch/middleware/actionable_exceptions.rb:17:in `call'
actionpack (6.0.2.1) lib/action_dispatch/middleware/debug_exceptions.rb:32:in `call'
web-console (4.0.1) lib/web_console/middleware.rb:132:in `call_app'
web-console (4.0.1) lib/web_console/middleware.rb:28:in `block in call'
web-console (4.0.1) lib/web_console/middleware.rb:17:in `catch'
web-console (4.0.1) lib/web_console/middleware.rb:17:in `call'
actionpack (6.0.2.1) lib/action_dispatch/middleware/show_exceptions.rb:33:in `call'
railties (6.0.2.1) lib/rails/rack/logger.rb:38:in `call_app'
railties (6.0.2.1) lib/rails/rack/logger.rb:26:in `block in call'
activesupport (6.0.2.1) lib/active_support/tagged_logging.rb:80:in `block in tagged'
activesupport (6.0.2.1) lib/active_support/tagged_logging.rb:28:in `tagged'
activesupport (6.0.2.1) lib/active_support/tagged_logging.rb:80:in `tagged'
railties (6.0.2.1) lib/rails/rack/logger.rb:26:in `call'
sprockets-rails (3.2.1) lib/sprockets/rails/quiet_assets.rb:13:in `call'
actionpack (6.0.2.1) lib/action_dispatch/middleware/remote_ip.rb:81:in `call'
actionpack (6.0.2.1) lib/action_dispatch/middleware/request_id.rb:27:in `call'
rack (2.2.2) lib/rack/method_override.rb:24:in `call'
rack (2.2.2) lib/rack/runtime.rb:22:in `call'
activesupport (6.0.2.1) lib/active_support/cache/strategy/local_cache_middleware.rb:29:in `call'
actionpack (6.0.2.1) lib/action_dispatch/middleware/executor.rb:14:in `call'
actionpack (6.0.2.1) lib/action_dispatch/middleware/static.rb:126:in `call'
rack (2.2.2) lib/rack/sendfile.rb:110:in `call'
actionpack (6.0.2.1) lib/action_dispatch/middleware/host_authorization.rb:83:in `call'
webpacker (4.2.2) lib/webpacker/dev_server_proxy.rb:23:in `perform_request'
rack-proxy (0.6.5) lib/rack/proxy.rb:57:in `call'
railties (6.0.2.1) lib/rails/engine.rb:526:in `call'
puma (4.3.1) lib/puma/configuration.rb:228:in `call'
puma (4.3.1) lib/puma/server.rb:681:in `handle_request'
puma (4.3.1) lib/puma/server.rb:472:in `process_client'
puma (4.3.1) lib/puma/server.rb:328:in `block in run'
puma (4.3.1) lib/puma/thread_pool.rb:134:in `block in spawn_thread'**

Answer 1

When you are calling the conversions method from the console, you are passing in a symbol :kg ... but when the method is being called in the controller, it's receiving a String.
So you just need to convert the unit of measure to a symbol, the same way you are converting the number value to an integer:
#result = UnitConverter::Weight.new.conversions(#input1.to_i , #input2.to_sym)
The error you got was b/c the lookup in your conversions table was essentially looking for Conversions['kg'] which returns nil -- hence the "undefined method keys..." error message.
Another solution, is to use a convenience method that Rails adds to the Hash class: with_indifferent_access.
If you define your lookup table like this (I'm omitting the guts of it), then you can access this Hash with either String keys or Symbol keys, and doing #input2.to_sym won't be necessary:
CONVERSIONS = {
...
}.with_indifferent_access