Wrong return value when calling a method - ruby-on-rails

I need to Add a tractor_beam instance method that takes a string description of an item as a parameter (e.g., "cow"). When called, the method should disable the shield, add the item to the inventory along with the ship's current location if it isn't too heavy to pick up (see algorithm below), enable the shield again, and return true. If the item is too heavy to pick up, the method should skip the inventory update and return false.
Algorithm:
An item is too heavy to pick up if its letters add up to more than 500. using .ord (Not very scientific, i know.) For example, the letters of cow add up to 329, so our tractor beam can abduct a cow, no problem.
My problem is that it returns nil and an empty hash, how do i break down the item to add each together?
Code:
class Spaceship
attr_accessor :name, :location, :item, :inventory
attr_reader :max_speed
def initialize (name, max_speed, location)
puts "Initializing new Spaceship"
#name = name
#max_speed = max_speed
#location = location
#item = item
#inventory = {}
end
def disable_shield
puts "Shield is off!"
end
def enable_shield
puts "Shield is on!"
end
def warp_to(location)
puts "Traveling at #{max_speed} to #{location}!"
#location = location
end
def tractor_beam(item)
disable_shield
item = item.split('')
item.each do |let|
let.ord
let + let.next
end
return item
if item > 500
enable_shield
#inventory[#location] = item
return true
else
return false
end
end
end
Driver Code:
uss_enterprise = Spaceship.new("USS Enterprise","200,000 mph", "China")
hms_anfromeda = Spaceship.new("HMS Andromeda", "108,277 mph", "China")
uss_enterprise.disable_shield
hms_anfromeda.enable_shield
p hms_anfromeda.location
hms_anfromeda.warp_to("Namibia")
p hms_anfromeda.location
hms_anfromeda.tractor_beam("cow")
p hms_anfromeda.item
Terminal:
Initializing new Spaceship
Initializing new Spaceship
Shield is off!
Shield is on!
"China"
Traveling at 108,277 mph to Namibia!
"Namibia"
Shield is off!
nil

Firstly, you have a return statement before your if conditional, so the conditional will never be ran. Remove that.
Secondly, you get the weight of the item by using ord, but you aren't assigning the value to anything:
item.each do |let|
let.ord
let + let.next
end
return item
if item > 500
This should do the trick:
item = item.split('')
weight = 0
item.each do |let|
weight += let.ord # add the ord of this letter to the weight
end
if weight > 500 # weight is now the ord of each letter of item 'cow'
enable_shield
#inventory[#location] = item
return true
else
return false
end

This line return item in your tractor_beam method will get run every time before getting to your if statement I think that is causing the problem.
Also you are not using the instance variable #item that you are created in the initialize method I think you might actually want something like this:
def tractor_beam(item)
disable_shield
#item = item.split('')
weight = 0
#item.each do |let|
weight += let.ord
end
if weight < 500
enable_shield
#inventory[#location] = #item
return true
else
return false
end
end
end

Related

array.select not iterating through every element

I have a rails controller and this code only loop through the first element in the metrics array? Why is that?
# /metrics/:id
def values
#metric = metrics.select do |metric|
id = metric['href'].split('/').last
p "id == params[:id] = #{id == params[:id]}" # false on the first iteration (but never gets to the next iteration
return id == params[:id]
end
p "HERE?" # We never get here!
end
You need to remove the return statement from your method, Ruby uses implicit return (see https://jtrudell.github.io/blog/ruby_return_values/), so the result of a block is the last line that is evaluated in that block, the return statement in your code is treated as a return from the values method. Your method needs to look something like:
def values
#metric = metrics.select do |metric|
metric['href'].split('/').last == params[:id]
end
end

Class variable access from top level

I am a complete beginner to Ruby. I am working on Lesson 45 of Learn Ruby the Hard Way currently and am creating a game similar to Zork and Adventure.
I have created a structure where I am creating 'scenes' in different files and requiring all the scenes in one file where I have an engine/map that ensures if the current scene does not equal 'finished' that it runs 'X' scene's 'enter' method.
However I have two issues:
1) I keep getting a error saying 'Warning class variable access from top level'
2) Even though the script is running I get
ex45.rb:30:in `play': undefined method `enter' for nil:NilClass (NoMethodError) from ex45.rb:59:in
The following is all of my code from each file. My apologies if it's a long read, but I would love to know why I am getting these two errors and what I can do to fix them.
Ex45.rb:
require "./scene_one.rb"
require "./scene_two.rb"
require "./scene_three.rb"
##action = SceneOne.new
##action_two = SceneTwo.new
##action_three = SceneThree.new
class Engine
def initialize(scene_map)
#scene_map = scene_map
end
def play()
current_scene = #scene_map.opening_scene()
last_scene = #scene_map.next_scene('finished')
while current_scene != last_scene
next_scene_name = current_scene.enter()
current_scene = #scene_map.next_scene(next_scene_name)
end
current_scene.enter()
end
end
class Map
##scenes = {
'scene_one' => ##action,
'scene_two' => ##action_two,
'scene_three' => ##action_three
}
def initialize(start_scene)
#start_scene = start_scene
end
def next_scene(scene_name)
val = ##scenes[scene_name]
return val
end
def opening_scene()
return next_scene(#start_scene)
end
end
a_map = Map.new('scene_one')
a_game = Engine.new(a_map)
a_game.play()
scene_one.rb:
class SceneOne
def enter
puts "What is 1 + 2?"
print "> "
answer = $stdin.gets.chomp
if answer == "3"
puts "Good job"
return 'scene_two'
else
puts "try again"
test
end
end
end
scene_two.rb
class SceneTwo
def enter
puts "1 + 3?"
print "> "
action = $stdin.gets.chomp
if action == "4"
return 'scene_three'
else
puts "CANNOT COMPUTE"
end
end
end
scene_three.rb
class SceneThree
def enter
puts "This is scene three"
end
end
Thanks in advance!
Answer to your first question:
You need to move the class variable definitions inside your Map class to get rid of these warnings:
Ex45.rb:5: warning: class variable access from toplevel
Ex45.rb:6: warning: class variable access from toplevel
Ex45.rb:7: warning: class variable access from toplevel
So, your Map class would look like this:
class Map
##action = SceneOne.new
##action_two = SceneTwo.new
##action_three = SceneThree.new
##scenes = {
'scene_one' => ##action,
'scene_two' => ##action_two,
'scene_three' => ##action_three
}
def initialize(start_scene)
#start_scene = start_scene
end
def next_scene(scene_name)
val = ##scenes[scene_name]
return val
end
def opening_scene()
return next_scene(#start_scene)
end
end
To answer your 2nd question:
You are getting undefined method 'enter' for nil:NilClass (NoMethodError) because your current_scene becomes nil at some point and then you try to call: current_scene.enter() i.e. nil.enter and it fails with that error message.
To solve this problem, you have to make sure you always have some value in your current_scene i.e. make sure it's not nil.
I think, you can just remove current_scene.enter() line from the end of your play method in the Engine class. So, your Engine class will look like this:
class Engine
def initialize(scene_map)
#scene_map = scene_map
end
def play()
current_scene = #scene_map.opening_scene()
last_scene = #scene_map.next_scene('finished')
while current_scene != last_scene
next_scene_name = current_scene.enter()
current_scene = #scene_map.next_scene(next_scene_name)
end
# current_scene.enter()
end
end
And, you won't get that error anymore.
Just so you know:
##y = 20
p Object.class_variables
--output:--
1.rb:1: warning: class variable access from toplevel
[:##y]
And:
class Object
def self.y
##y
end
end
puts Object.y
--output:--
20
But:
class Dog
##y = "hello"
def self.y
##y
end
end
puts Dog.y #=>hello
puts Object.y #=>What do you think?
The output of the last line is the reason that class variables are not used in ruby. Instead of class variables, you should use what are known as class instance variables:
class Object
#y = 10 #class instance variable
def self.y
#y
end
end
puts Object.y
class Dog
#y = "hello"
def self.y
#y
end
end
puts Dog.y #=> hello
puts Object.y #=> 10
A class instance variable is just an #variable that is inside the class, but outside any def. And instead of there being one ##variable that is shared by all the subclasses, each subclass will have its own #variable.

rails model action check

I have Coupon model and in this model file I have a suitable_for_use method.I want to list Coupons if coupon.suitable_for_use == true.Is there any short way to do this ? I wrote this code but it doesn't work.
#coupons = []
coupons = Coupon.all.each do |coupon|
if coupon.suitable_for_use
#coupons << coupon
end
end
#coupons = coupons
suitable_for_use method
def suitable_for_use
result = true
if is_used?
result = false
elsif self.start > Time.now.in_time_zone
result = false
elsif self.end < Time.now.in_time_zone
result = false
end
return result
end
The problem is your assigning twice to #coupons. The return value from each is the collection it was given. So your last line reassigns the original set of coupons returned by Coupon.all.
#coupons = Coupon.all.select(&:suitable_for_use)
If your not sure what that does, here's the expanded version.
#coupons = Coupon.all.select {|coupon| coupon.suitable_for_select}
Basically, select takes a block that it will iterate over and if the block returns true then it will add that element to the returned collection. So any coupon that returns false will not be returned by select.
The &:suitable_for_use is called a symbol to proc. It literally expands to the block in the second line and is pretty common in ruby one-liners.

Nested ActiveRecords: Find many childrens of many parents

In my Rails 3.2 app a Connector has_many Incidents.
To get all incidents of a certain connector I can do this:
(In console)
c = Connector.find(1) # c.class is Connector(id: integer, name: string, ...
i = c.incidents.all # all good, lists incidents of c
But how can I get all incidents of many connectors?
c = Connector.find(1,2) # works fine, but c.class is Array
i = c.incidents.all #=> NoMethodError: undefined method `incidents' for #<Array:0x4cc15e0>
Should be easy! But I don't get it!
Here’s the complete code in my statistics_controller.rb
class StatisticsController < ApplicationController
def index
#connectors = Connector.scoped
if params['connector_tokens']
logger.debug "Following tokens are given: #{params['connector_tokens']}"
#connectors = #connectors.find_all_by_name(params[:connector_tokens].split(','))
end
#start_at = params[:start_at] || 4.weeks.ago.beginning_of_week
#end_at = params[:end_at] || Time.now
##time_line_data = Incident.time_line_data( #start_at, #end_at, 10) #=> That works, but doesn’t limit the result to given connectors
#time_line_data = #connectors.incidents.time_line_data( #start_at, #end_at, 10) #=> undefined method `incidents' for #<ActiveRecord::Relation:0x3f643c8>
respond_to do |format|
format.html # index.html.haml
end
end
end
Edit with reference to first 3 answers below:
Great! With code below I get an array with all incidents of given connectors.
c = Connector.find(1,2)
i = c.map(&:incidents.all).flatten
But idealy I'd like to get an Active Records object instead of the array, because I'd like to call where() on it as you can see in methode time_line_data below.
I could reach my goal with the array, but I would need to change the whole strategy...
This is my time_line_data() in Incidents Model models/incidents.rb
def self.time_line_data(start_at = 8.weeks.ago, end_at = Time.now, lim = 10)
total = {}
rickshaw = []
arr = []
inc = where(created_at: start_at.to_time.beginning_of_day..end_at.to_time.end_of_day)
# create a hash, number of incidents per day, with day as key
inc.each do |i|
if total[i.created_at.to_date].to_i > 0
total[i.created_at.to_date] += 1
else
total[i.created_at.to_date] = 1
end
end
# create a hash with all days in given timeframe, number of incidents per day, date as key and 0 as value if no incident is in database for this day
(start_at.to_date..end_at.to_date).each do |date|
js_timestamp = date.to_time.to_i
if total[date].to_i > 0
arr.push([js_timestamp, total[date]])
rickshaw.push({x: js_timestamp, y: total[date]})
else
arr.push([js_timestamp, 0])
rickshaw.push({x: js_timestamp, y: 0})
end
end
{ :start_at => start_at,
:end_at => end_at,
:series => rickshaw #arr
}
end
As you only seem to be interested in the time line data you can further expand the map examples given before e.g.:
#time_line_data = #connectors.map do |connector|
connector.incidents.map do |incident|
incident.time_line_data(#start_at, #end_at, 10)
end
end
This will map/collect all the return values of the time_line_data method call on all the incidents in the collection of connectors.
Ref:- map
c = Connector.find(1,2)
i = c.map(&:incidents.all).flatten

Rails - Triggering Flash Warning with method returning true

I'm trying to trigger a warning when a price is entered too low. But for some reason, it always returns true and I see the warning regardless. I'm sure there something wrong in the way I'm doing this as I'm really new to RoR.
In model:
def self.too_low(value)
res = Class.find_by_sql("SELECT price ……. WHERE value = '#{value}'")
res.each do |v|
if #{value} < v.price.round(2)
return true
else
return false
end
end
end
In controller:
#too_low = Class.too_low(params[:amount])
if #too_low == true
flash[:warning] = 'Price is too low.'
end
I would write it somewhat different. You iterate over all items, but you are only interested in the first element. You return from inside the iteration block, but for each element the block will be executed. In ruby 1.9.2 this gives an error.
Also i would propose using a different class-name (Class is used to define a class)
So my suggestion:
Class YourGoodClassName
def self.too_low(amount)
res = YourGoodClassName.find_by_sql(...)
if res.size > 0
res[0].price.round(2) < 1.00
else
true
end
end
end
You can see i test if any result is found, and if it is i just return the value of the test (which is true or false); and return true if no price was found.
In the controller you write something like
flash[:warning] = 'Price is too low' if YourGoodClassName.too_low(params[:amount])

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