ruby-on-rails - 在每个循环的 Ruby on Rails 中，如果没有迭代，是否有一种好方法可以做某事？

Question

有没有一种简单的说法：否则，如果没有任何循环，则显示“无对象”。似乎应该有一种很好的语法方法来做到这一点，而不是计算 @user.find_object("param") 的长度

Answer 1

您可以执行以下操作：

if @collection.blank?
  # @collection was empty
else
  @collection.each do |object|
    # Your iteration  logic
  end
end

Answer 2

导轨视图

# index.html.erb
<h1>Products</h1>
<%= render(@products) || content_tag(:p, 'There are no products available.') %> 

# Equivalent to `render :partial => "product", @collection => @products

render(@products)为空nil时将返回。@products

红宝石

puts "no objects" if @collection.blank?

@collection.each do |item|
  # do something
end

# You *could* wrap this up in a method if you *really* wanted to:

def each_else(list, message)
  puts message if list.empty?

  list.each { |i| yield i }
end

a = [1, 2, 3]

each_else(a, "no objects") do |item|
  puts item
end

1
2
3
=> [1, 2, 3]

each_else([], "no objects") do |item|
  puts item
end

no objects
=> []

Answer 3

if @array.present?
  @array.each do |content|
    #logic
  end
else
  #your message here
end

Answer 4

我执行以下操作：

<% unless @collection.empty? %>
<% @collection.each do |object| %>
    # Your iteration  logic
  <% end %>
<% end %>