[RUBY] if ~ .length! = 0 Find an empty value

Empty value

When implementing the function of displaying the products listed as an issue in a list I was writing a conditional expression in an if statement

that is,

When the instance variable is empty, show a dummy product instead

something like

if statement This started to work enthusiastically with ease I finished writing and confirmed the behavior ...

Dummy products are not displayed!

items_controller.rb

 def index
    @items = Item.order('created_at DESC')
  end

ruby:index.html.erb

####################↓ Display the products saved in the DB ↓####################
<ul class='item-lists'>
    <% if @items %>
      <% @items.each do |item| %>
        <li class='list' >
          <%= link_to item_path(item.user_id) do %>
            <div class='item-img-content'>
            </div>
            <div class='item-info'>
              <h3 class='item-name'>
                <%= item.name %>
              </h3>
              <div class='item-price'>
                <span><%= item.price %>Circle<br>(tax included)</span>
                <div class='star-btn'>
                  <%= image_tag "star.png ", class:"star-icon" %>
                  <span class='star-count'>0</span>
                </div>
              </div>
            </div>
          <% end %>
        </li>
      <% end %>

####################↓ The following are dummy products ↓####################
    <% else %>
        <li class='list'>
          <%= link_to '#' do %>
          <%= image_tag "https://s3-ap-northeast-1.amazonaws.com/mercarimaster/uploads/captured_image/content/10/a004.png ", class: "item-img" %>
          <div class='item-info'>
            <h3 class='item-name'>
Selling goods
            </h3>
            <div class='item-price'>
              <span>0 Yen<br>(tax included)</span>
              <div class='star-btn'>
                <%= image_tag "star.png ", class:"star-icon" %>
                <span class='star-count'>0</span>
              </div>
            </div>
          </div>
          <% end %>
        </li>
    <% end %>
    </ul>
  </div>

"In short, if the DB is empty, the instance variables will also be empty, right?" It was working based on the idea

I was at that time

"When the instance variable is empty"

I remember being obsessed with the word If only that is suppressed ...! I was convinced that it was too mysterious when I think about it now

Conviction is sometimes synonymous with stop thinking

After an hour, I finally had some doubts in myself. "... Maybe just because the table is empty doesn't mean that the contents of what you generate will be empty, right?" And the contents of params

I remembered that it was an array

An empty value can be entered, and even if the content is completely empty, it will not be recognized as empty when the array exists.

I have to prove that it's an empty value, but it's not empty

I asked the instructor for help The answer returned is

"If the contents of an instance variable are empty and you want to return false, but an array is created, why not judge whether the number of elements in the array is 0?"

It was

In other words, like this!

ruby:index.html.erb

<ul class='item-lists'>
    <% if @items.length != 0 %> #← Here!
      <% @items.each do |item| %>
        <li class='list' >
          <%= link_to item_path(item.user_id) do %>
#The following is omitted

Know the interpretation

In other words

The DB will be empty, but the contents of the instance variable will be an array, so let's judge whether the contents are empty or not.

something like By passing the number of arrays in .length and specifying! = 0 If it is not 0, true will be returned.

There was a clear and refreshing understanding because I was presented with something that I had never thought of. At the same time, there was also the regret that I thought, "Did you notice it?"

Lesson

The lesson learned this time is not related to one idea To see things from a more bird's-eye view