序列化 to_xml 时出现 NoMethodError

Question

我尝试从数据库中获取一些模型对象并将它们序列化为 xml，但是当包含特定的 (has_many) 关联时，我收到以下错误。 JSON 序列化 (to_json) 没有问题（也包括属性）。还有一个对象（XML 和 JSON）的序列化。问题可能是什么？ （模型类没有覆盖任何 XML 序列化的东西，我使用的是 Rails 3）。

这里是命令：
Entity.all.to_xml :include => :properties

和转储：

NoMethodError：nil 的未定义方法“宏”：NilClass 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activesupport-3.0.1/lib/active_support/whiny_nil.rb:48:in `method_missing' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activerecord-3.0.1/lib/active_record/serialization.rb:41:in `serializable_add_includes' 来自/home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activerecord-3.0.1/lib/active_record/serialization.rb:40:in `each' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activerecord-3.0.1/lib/active_record/serialization.rb:40:in `serializable_add_includes' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activerecord-3.0.1/lib/active_record/serializers/xml_serializer.rb:191:in `send' 来自/home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activerecord-3.0.1/lib/active_record/serializers/xml_serializer.rb:191:in `add_includes' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activerecord-3.0.1/lib/active_record/serializers/xml_serializer.rb:186:in `add_extra_behavior' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activemodel-3.0.1/lib/active_model/serializers/xml.rb:103:in `serialize' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/builder-2.1.2/lib/builder/xmlbase.rb:134:in `call' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/builder-2.1.2/lib/builder/xmlbase.rb:134:in `_nested_structures' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/builder-2.1.2/lib/builder/xmlbase.rb:58:in `method_missing' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/builder-2.1.2/lib/builder/xmlbase.rb:31:in `tag!' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activemodel-3.0.1/lib/active_model/serializers/xml.rb:101:in `serialize' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activerecord-3.0.1/lib/active_record/serializers/xml_serializer.rb:175:in `to_xml' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activerecord-3.0.1/lib/active_record/associations/association_proxy.rb:218:in `send' 来自/home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activerecord-3.0.1/lib/active_record/associations/association_proxy.rb:218:in `method_missing' ... 5 级... 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/builder-2.1.2/lib/builder/xmlbase.rb:134:in `call' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/builder-2.1.2/lib/builder/xmlbase.rb:134:in `_nested_structures' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/builder-2.1.2/lib/builder/xmlbase.rb:58:in `method_missing' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/builder-2.1.2/lib/builder/xmlbase.rb:31:in `tag!' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activemodel-3.0.1/lib/active_model/serializers/xml.rb:101:in `serialize' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activerecord-3.0.1/lib/active_record/serializers/xml_serializer.rb:175:in `to_xml' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activesupport-3.0.1/lib/active_support/xml_mini.rb:107:in `to_tag' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activesupport-3.0.1/lib/active_support/core_ext/array/conversions.rb:159:in `to_xml' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activesupport-3.0.1/lib/active_support/core_ext/array/conversions.rb:159:in `each' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activesupport-3.0.1/lib/active_support/core_ext/array/conversions.rb:159:in `to_xml' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/builder-2.1.2/lib/builder/xmlbase.rb:134:in `call' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/builder-2.1.2/lib/builder/xmlbase.rb:134:in `_nested_structures' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/builder-2.1.2/lib/builder/xmlbase.rb:58:in `method_missing' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activesupport-3.0.1/lib/active_support/core_ext/array/conversions.rb:158:in `__send__' 来自 /home/kai/.rvm/gems/ruby-1.8.7-p302@projectx/gems/activesupport-3.0.1/lib/active_support/core_ext/array/conversions.rb:158:in `to_xml'

更新及解决方案

HoBlend 是对的......实体模型中的关联之一没有正确设置，但不是properties 之一。
在实体中还有一个与用户模型的关联：
belongs_to :created_by, :class_name => "User", :foreign_key => "created_by"
如果您习惯于使用 ActiveRecord 关联，您会发现 :foreign_key 参数在此处无效（它必须在关联的另一端，它也是）。 Rails 从来没有抱怨过这个参数，我的测试都通过了。但它使 XML 序列化以某种方式失败（令人惊讶的是不是 JSON 序列化）。

更新更新

ActiveRecord 中似乎存在错误。考虑以下模型：

class User < ActiveRecord::Base
  has_many :created_entities, :class_name => "Entity", :foreign_key => "created_by"
end

class Entity < ActiveRecord::Base
  belongs_to :created_by, :class_name => "User", :foreign_key => "created_by"
end

实体迁移中存在created_by 整数字段。似乎当您将 belongs_to 关联命名为与 :foreign_key 相同时，XML 序列化就会中断。一旦我更改为belongs_to :creator, :class_name => "User", :foreign_key => "created_by"，序列化就会按预期工作。

更新更新更新;-)

这已经在 Rails 3.0.3 中解决了（我有 3.0.1）。那我学什么……先更新软件！

Answer 1

很可能模型关系设置不正确。 你能做到吗：

e = Entity.find.first 电子财产

并让它返回关联的对象？