创建实例时初始化哈希变量答案

【问题标题】：Initializing a hash variable when creating an instance创建实例时初始化哈希变量
【发布时间】：2010-12-06 11:48:15
【问题描述】：

当我创建 SomeClass 的实例时，我试图将类变量初始化为哈希，但我一直收到错误消息。对 ruby 来说有点新，所以任何帮助都将不胜感激。谢谢

class SomeClass < ActiveRecord::Base  
  attr_accessible :some_hash  
  serialize :some_hash,   Hash  

  def initialize(args = {})  
    @some_hash != {}  
  end  
end

NoMethodError：未定义的方法has_key?' for nil:NilClass from /opt/local/lib/ruby/gems/1.8/gems/activesupport-2.3.8/lib/active_support/whiny_nil.rb:52:inmethod_missing'
来自 /opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:2827:in has_attribute?' from /opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:2888:ininspect'
来自 /opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:2887:in collect' from /opt/local/lib/ruby/gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:2887:ininspect'
来自 /opt/local/lib/ruby/1.8/irb.rb:310:in output_value' from /opt/local/lib/ruby/1.8/irb.rb:159:ineval_input'
来自 /opt/local/lib/ruby/1.8/irb.rb:271:in signal_status' from /opt/local/lib/ruby/1.8/irb.rb:155:ineval_input'
来自 /opt/local/lib/ruby/1.8/irb.rb:154:in eval_input' from /opt/local/lib/ruby/1.8/irb.rb:71:instart'
来自 /opt/local/lib/ruby/1.8/irb.rb:70:in catch' from /opt/local/lib/ruby/1.8/irb.rb:70:instart'
来自 /opt/local/bin/irb:13

【问题讨论】：

标签： ruby-on-rails

【解决方案1】：

这个article 应该可以帮到你。

在 Ruby 中，您可以通过简单地重新定义方法（“monkey patching”）轻松地覆盖 gems 中的现有代码

这是你重写的#initialize 方法：

# active_record/base.rb
  def initialize(attributes = nil)
    @attributes = attributes_from_column_definition
    @attributes_cache = {}
    @new_record = true
    @readonly = false
    @destroyed = false
    @marked_for_destruction = false
    @previously_changed = {}
    @changed_attributes = {}

    ensure_proper_type

    populate_with_current_scope_attributes
    self.attributes = attributes unless attributes.nil?

    result = yield self if block_given?
    _run_initialize_callbacks
    result
  end

【讨论】：