Rubyonrails Rails：比枚举更惯用的排序可比较列表方法

也许scope个就是你想要的.挑你喜欢的:

class Model < ApplicationRecord
  enum :priority, {low: 10, moderate: 20, high: 30, very_high: 40}

  ##
  # Add scopes, aka class methods. Append `.order(:priority)` if you like
  #
  #   Model.min_priority(:high).pluck(:priority)
  #   #=> ["high", "high", "very_high"]
  #
  scope :min_priority, ->(name) { where("priority >= ?", priorities[name]) }
  scope :max_priority, ->(name) { where("priority <= ?", priorities[name]) }


  ##
  # Add a shortcut method
  #
  #   Model.first.rank > Model.last.rank
  #   #=> false
  #
  def rank
    priority_before_type_cast
  end


  ##
  # Define the methods you need
  #
  #   Model.first.gt(Model.last)
  #   #=> false
  #
  def rank = priority_before_type_cast
  def gt(other)   = (rank >  other.rank)
  def gteq(other) = (rank >= other.rank)
  def lt(other)   = (rank <  other.rank)
  def lteq(other) = (rank <= other.rank)


  ##
  # You could include Comparable into the model, which will give you:
  # <, <=, >, >=, ==, between?, clamp
  # However, `==` method will cause different models with the same priority
  # to be equal each other. Other than that, you can compare your models:
  #
  #   Model.first <= Model.last
  #   #=> true
  #
  alias_method :eq_copy, :==   # copy the == method
  include Comparable
  alias_method :==, :eq_copy   # put it back
  remove_method :eq_copy       # get rid of the witness
  # this defines how your models compare to each other, aka spaceship operator
  def <=> other
    priority_before_type_cast <=> other.priority_before_type_cast
  end
end

您可能不想将Comparable包含在模型中，但仅定义<=>也很有用，因为当您使用sort时，您会比较:

>> Model.all.pluck(:priority)
=> ["low", "moderate", "high", "very_high", "low", "low"]

>> Model.all.sort.pluck(:priority)
=> ["low", "low", "low", "moderate", "high", "very_high"]

但sort_by可以在没有额外服务的情况下解决这个问题，而且速度更快.(use 101 if applicable instead):

>> Model.all.sort_by(&:priority_before_type_cast) # or sort_by(&:rank)
=>
[#<Model:0x00007f99f1380b98 id: 1, priority: "low">,
 #<Model:0x00007f99f06ad178 id: 5, priority: "low">,
 #<Model:0x00007f99f06ad0d8 id: 6, priority: "low">,
 #<Model:0x00007f99f06ad358 id: 2, priority: "moderate">,
 #<Model:0x00007f99f06ad2b8 id: 3, priority: "high">,
 #<Model:0x00007f99f06ad218 id: 4, priority: "very_high">]

还有一件事你可以做，以获得任意的顺序:

Model.in_order_of(:priority, [:low, :moderate, :high, :very_high])