在Ruby on Rails的每个循环中,如果没有迭代,有没有一种好的方法可以做某些事情？

Question

有没有简单的说法:否则,如果没有任何循环,请显示"没有对象".似乎应该有一个很好的语法方法来做这个而不是计算@ user.find_object("param")的长度

Answer 1

你可以这样做:

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

Answer 2

Rails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)nil当@products空的时候会返回.

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
=> []