Question

我已经在rails中实现了继承，并从Person类中获取了子孙。

但现在我想使用简单的ruby类从Person类中获取子孙，而不使用ActiveRecord。

我设法从一个人对象中获取孩子。请指导我如何从Person实例中获取孙子。

class Person
  attr_accessor :name, :age
  attr_reader :ref

 def initialize(name, ref)
   @name = name
   @ref = ref
 end
end

class Parent < Person
  attr_reader :children

  def initialize(names = %w(A B C))
   @children = names.map do |n|
     Person.new(n, self)
    end
  end
end


bar = Parent.new.children.first
bar.ref

Answer 1

如果父，子和granchild之间没有行为差异，那么可以使用一个类建模：

class Person

  attr_reader :children
  attr_reader :name

  def initialize(name, children: [])
    @name = name
    @children = children
  end

  def grandchildren
    @children.flat_map(&:children)
  end

end

我们添加了一个#grandchildren方法，询问每个孩子的孩子。此示例显示了它的工作原理：

sally = Person.new("Sally")
fred = Person.new("Fred", children: [sally])
mary = Person.new("mary", children: [fred])
p mary.children.map(&:name)         # => ["Fred"]
p mary.grandchildren.map(&:name)    # => ["Sally"]

Answer 2

让我们通过NameMagic（gem y_support/name_magic，gem install y_support安装）将问题简化为最低要求：

require 'y_support/name_magic'

class Person
  include NameMagic
  attr_accessor :children

  def initialize( children: [] )
    @children = Array( children )
  end

  def grandchildren
    children.map( &:children ).flatten.uniq
  end
end

现在NameMagic负责为您命名，同时您负责定义家谱：

Mary = Person.new
Fred, Joe = Person.new, Person.new
Mary.children << Fred << Joe
Sally, Sam = Person.new, Person.new
Fred.children << Sally << Sam
Jane = Person.new
Joe.children << Jane

然后

Mary.grandchildren
#=> [Sally, Sam, Jane]

请注意，y_support/name_magic允许您仅通过常量赋值来命名对象，并告诉inspect方法显示名称。它还会自动处理:name构造函数的new关键字参数：

Joe.children << Person.new( name: :Mike )
# now Mary has 4 grandchildren
Mary.grandchildren
#=> [Sally, Sam, Jane, Mike]

Answer 3

你们都比我快。但是，有时孩子会有新的孩子：

suzie   = Person.new(name: 'Suzie')
bobby   = Person.new(name: 'Bobby')
harriet = Person.new(name: 'Harriet')
suzie.children = [bobby, harriet]

苏西有两个孩子，鲍比和哈丽特：

puts "Suzie has #{suzie.grandchildren.count} grandchildren named #{suzie.grandchildren.map(&:name)}"
=> Suzie has 0 grandchildren named []

但是，可怜的苏西没有孙子：

ralph   = Person.new(name: 'Ralph')
madge   = Person.new(name: 'Madge')
bea     = Person.new(name: 'Bea')

bobby.children = [ralph]
harriet.children = [madge, bea]

但是，那小小的祝福来了：

puts "Suzie has #{suzie.grandchildren.count} grandchildren named #{suzie.grandchildren.map(&:name)}"
Suzie has 3 grandchildren named ["Ralph", "Madge", "Bea"]

现在Suzie是一个快乐的奶奶：

johnny = Person.new(name: 'Johhny')
bobby.children = [johnny]

puts "Suzie has #{suzie.grandchildren.count} grandchildren named #{suzie.grandchildren.map(&:name)}"
=> Suzie has 4 grandchildren named ["Ralph", "Johhny", "Madge", "Bea"]

Bobby不停地来：

{{1}}

感谢Wayne for flat_map！

从简单的红宝石中获取来自Person实例的孙子

3 个答案: