Question

我有一个哈希列表，如下：

incoming_links = [
 {:title => 'blah1', :url => "http://blah.com/post/1"},
 {:title => 'blah2', :url => "http://blah.com/post/2"},
 {:title => 'blah3', :url => "http://blah.com/post/3"}]

一个ActiveRecord模型，其中包含一些匹配行的数据库中的字段，例如：

Link.all => 
[<Link#2 @title='blah2' @url='...post/2'>,
 <Link#3 @title='blah3' @url='...post/3'>,
 <Link#4 @title='blah4' @url='...post/4'>]

我想在Link.all上使用incoming_links进行设置操作，以便我可以发现<Link#4 ...>不在incoming_links和{{{ 1}}不在{:title => 'blah1', :url =>'http://blah.com/post/1'}集合中，如此：

Link.all

糟糕的解决方案a）：

我宁愿不重写#pseudocode #incoming_links = as above links = Link.all expired_links = links - incoming_links missing_links = incoming_links - links expired_links.destroy missing_links.each{|link| Link.create(link)}等等，我也可以将Array#-转换为一组未保存的incoming_links个对象;所以我尝试在Link中覆盖hash eql?等等，以便忽略Link默认提供的id等式。但这是在应用程序中应该考虑这种平等的唯一地方 - 在其他地方需要Link＃id默认标识。有没有什么方法可以将Link子类化并应用AR::Base，hash等覆盖那里？

糟糕的解决方案b）：

我尝试过的另一条路线是为每个链接提取属性哈希并执行eql?以修剪哈希值。但这需要编写单独的.slice('id',...etc)方法，以便在对哈希进行集合操作时跟踪链接对象，并编写单独的代理类来包装-哈希和链接，这看起来有点矫枉过正。尽管如此，对我来说这是current solution。

您能想到设计此互动的更好方法吗？额外的清洁信用。

Answer 1

试试这个

incoming_links = [
 {:title => 'blah1', :url => "http://blah.com/post/1"},
 {:title => 'blah2', :url => "http://blah.com/post/2"},
 {:title => 'blah3', :url => "http://blah.com/post/3"}]

ar_links = Link.all(:select => 'title, url').map(&:attributes)

# wich incoming links are not in ar_links
incoming_links - ar_links

# and vice versa
ar_links - incoming_links

<强> UPD

对于您的链接模型：

def self.not_in_array(array)
  keys = array.first.keys
  all.reject do |item|
    hash = {}
    keys.each { |k| hash[k] = item.send(k) }
    array.include? hash
  end
end

def self.not_in_class(array)
  keys = array.first.keys
  class_array = []
  all.each do |item|
    hash = {}
    keys.each { |k| hash[k] = item.send(k) }
    class_array << hash
  end
  array - class_array
end

ar = [{:title => 'blah1', :url => 'http://blah.com/ddd'}]
Link.not_in_array ar
#=> all links from Link model which not in `ar`
Link.not_in_class ar
#=> all links from `ar` which not in your Link model

Answer 2

如果你重写了相等方法，ActiveRecord会抱怨吗？

你不能做类似的事情（比如常规的ruby类）：

class Link
  attr_reader :title, :url

  def initialize(title, url)
    @title = title
    @url = url
  end

  def eql?(another_link)
    self.title == another_link.title and self.url == another_link.url
  end

  def hash
     title.hash * url.hash
  end
end

aa = [Link.new('a', 'url1'), Link.new('b', 'url2')]
bb = [Link.new('a', 'url1'), Link.new('d', 'url4')]

(aa - bb).each{|x| puts x.title}

Answer 3

要求是：

#  Keep track of original link objects when 
#   comparing against a set of incomplete `attributes` hashes.
#  Don't alter the `hash` and `eql?` methods of Link permanently, 
#   or globally, throughout the application.

当前解决方案使用Hash的eql?方法生效，并使用原始对象注释哈希：

class LinkComp < Hash
  LINK_COLS = [:title, :url]
  attr_accessor :link
  def self.[](args)
    if args.first.is_a?(Link) #not necessary for the algorithm, 
                              #but nice for finding typos and logic errors
      links = args.collect do |lnk|
         lk = super(lnk.attributes.slice(*(LINK_COLS.collect(&:to_s)).to_a)
         lk.link = lnk
         lk
      end
    elsif args.blank?
       []
    #else #raise error for finding typos
    end        
  end
end

incoming_links = [
 {:title => 'blah1', :url => "http://blah.com/post/1"},
 {:title => 'blah2', :url => "http://blah.com/post/2"},
 {:title => 'blah3', :url => "http://blah.com/post/3"}]

#Link.all => 
#[<Link#2 @title='blah2' @url='...post/2'>,
# <Link#3 @title='blah3' @url='...post/3'>,
# <Link#4 @title='blah4' @url='...post/4'>]

incoming_links= LinkComp[incoming_links.collect{|i| Link.new(i)}]
links = LinkComp[Link.all] #As per fl00r's suggestion 
                           #this could be :select'd down somewhat, w.l.o.g.

missing_links =  (incoming_links - links).collect(&:link)
expired_links = (links - incoming_links).collect(&:link)

比较字段哈希与等效AR对象的列表

3 个答案: