ruby on rails -如何检索值为true的实例属性名

Question

我使用Ruby on Rails 3.2.9和Ruby 1.9.3。我有一个符号数组和一个模型类(ActiveModel)，这些符号(更多其他)作为布尔属性。给定一个类实例，我想检索其值为true的所有属性名。即:

# Given an array of symbols
[:attr_1, :attr_2, :attr_3]
# Given a class instance
<#Model attr_1: true, attr_2: false, attr_3: false, attr_4: true, ... attr_N: true>
# Then I would like to return
[:attr_1, :attr_4, ..., :attr_N]

我怎么做呢?

Answer 1

attrs = [:attr_1, :attr_2, :attr_3]
class Model
  def are_true?(attr_names)
    eval(attr_names.map {|a| "send(:#{a})"}.join(" && "))
  end
  def which_true?(attr_names)
    attr_names.map {|a| a if send(a) == true}.compact
  end
end
m = <#Model attr_1: true, attr_2: false, attr_3: false, attr_4: true, ... attr_N: true>
m.are_true?(attrs)  # evals if all given attr_names are true
m.which_true?(attrs) # returns array of attr_names which are true

Answer 2

如果您有符号列表，您可以遍历它们并选择为真

symbols = [:attr_1, :attr_2, :attr_3]
symbols.select {|sym| object.send(sym) == true }

如果你没有你想要的符号列表，你可以简单地遍历模型的所有属性

symbols = object.attributes
symbols.select {|sym| object.send(sym) == true }