如何知道今天是本月的周一，周二，周三等（数量）？(How to know today is which Monday, Tuesday, Wednesday, etc. (in number) of this month?)

 一些提示。 
 
 代替 
 
@lawn = Lawn.where("selected = ?", "true")
 
 最好在模型中添加范围。 @lawn是一个对象数组，因此请使用复数。 
 
  def display_lawns
    @lawns = Lawn.all
  end

  def display_status
   @lawns = Lawn.all.where("selected = ?", "true")
  end
 
 @lawns是一个数组，所以你不能使用@lawn.description 
 
 如果您需要数组的第一项， @lawn.first.description可以正常工作 
 
<h2><%= @lawns.first.description %></h2>
<ul>
  <% @lawns.each do |lawn| %>
    <li>
      <%= lawn.description %>
      <%= button_to "Select", update_booking_path(booking_id: lawn.booking), remote: true %>
    </li>
  <% end %>
</ul>

A couple of hints.
 
Instead of 
 
@lawn = Lawn.where("selected = ?", "true")
 
Is better to add a scope in your model. @lawn is an array of objects, so use plural.
 
  def display_lawns
    @lawns = Lawn.all
  end

  def display_status
   @lawns = Lawn.all.where("selected = ?", "true")
  end
 
@lawns is an array, so you can't use @lawn.description
 
@lawn.first.description works if you need the first item of the array
 
<h2><%= @lawns.first.description %></h2>
<ul>
  <% @lawns.each do |lawn| %>
    <li>
      <%= lawn.description %>
      <%= button_to "Select", update_booking_path(booking_id: lawn.booking), remote: true %>
    </li>
  <% end %>
</ul>