Ruby rails 不创建实例变量

Question

I am using a lynda.com tutorial for Ruby on Rails. The very first instance of creating and using array instance variables does not work. At first I thought it was that @array might have become a reserve word in the newer 5.0 version of rails that I am using, but changing it did not cause the "nil" (undefined) error to go away.

What is wrong with Ruby Rails 5.0? It is refusing to define instance variables and to pass them to the appropriate template.

This is extremely aggravating, since rails is not behaving as documented (ie RAILS IS BRAIN DEAD OUT OF THE BOX).

****************
demo_controller.rb

class DemoController < ApplicationController

  def index
    render('hello')
  end

  def hello
     @zarray = [1,2,3,4,5]  <------------ this is defined
  end

  def other_hello
    render(:text => "Hello EVERYONE!")
  end

end

******************
hello.html.erb

<h1>Demo#hello</h1>

<p>Hello World!</p>

<%= 1 + 1 %>   <------ works
<% target = "world" %>
</br>
<%= "Hello #{target}" %>   <----- works
</br>
<% @zarray.each do |n| %>   <---- line 10.  Rails claims that @zarray is 
not defined
  <%= n %></br>
<% end %>

ActionView::Template::Error (undefined method `each' for nil:NilClass):

Answer 1

I copied and ran your code and it worked fine. I guess it could be down to the fact that controllers should as a rails convention be pluralized, and your controller is called DemoController and perhaps you've called demo S #action somewhere? So, generate a new controller from your terminal called:

DemosController

with the generator:

rails g controller Demos

And copy paste everything from the old controller to the new controller. And in your routes.rb you need to first make sure you have the correct resources :demos (the name of your model) which will give you the standard RESTful resources ( index , new , create , etc), but as your ' hello ' method is not a part of the RESTful api, you need to create a custom route for that:

  get 'hello' => 'demos#hello',  :as => :hello

get = HTTP method

' hello ' = The URL you want to hello.html.erb to be reachable on: localhost:3000/hello

' demos#hello ' = demos is the DemosController and #hello is the action in the controller.

' :as => :hello ' (_path)is the named helper you can call in a link_to on any page for instance: link_to hello_path.

Answer 2

I am new to Ruby and Rails. I tested using a plain STRING instance variable, and THAT got passed from my controller to my template, so the issue was the array definition. Apparently the older form of array definition that was in the tutorial that I was using no longer works in the version of rails and ruby that I am using.

I am using Ruby on Rails 5.0.1 with Ruby 2.2.4p230 (2015-12-16 revision 53155) [i386-mingw32] on Windows (rails/ruby compatibility is kosher).

@zarray = [1,2,3,4,5]     <-- the array is not defined when passed to template
@zarray = Array.new << 1 << 2 << 3 << 4 << 5      <-- this works

It is a bit distressing that Ruby does not even BOTHER to complain about the format of the array definition. It just DOES NOTHING (ie, refuses to initialize the array).

In the template:

<% @zarray.each do |n| %>
  <%= n %></br>
<% end %>

I should add that @zarray = {1,2,3,4,5] works if you use it after @zarray = Array.new

In other words, at some point in the evolution of Ruby, EXPLICITLY classing arrays was introduced? It is not always clear in the documentation. The earlier tutorial I was using does NOT explicitly class the array.

---

The problem seems to be in the current RAILS version (5.0.1) that I am running. I has done SOMETHING to destroy the ability of Ruby to create an array using array literal syntax. When I run array definitions with literal syntax in IRB, I have no problem creating them. So Ruby is fine. It is a serious BUG in the 5.0.1 version of rails. So I think I should report it.

Welcome to Git (version 1.8.1.2-preview20130201)
$ irb
irb(main):002:0> service_mileage = [5000,15000,30000,60000,100000]
=> [5000, 15000, 30000, 60000, 100000]
irb(main):003:0> service_mileage[0]
=> 5000
irb(main):004:0> service_mileage[2]
=> 30000
irb(main):005:0>