ActiveRecord中集合的Ruby类型

如果我在ActiveRecord中有一个包含子对象集合的对象，即

class Foo < ActiveRecord::Base
  has_many :bars, ...
end

我收到：

ActiveRecord::RecordNotFound: Couldn't find Bar without an ID

我认为这是因为ActiveRecord为了自己的目的劫持了

find

方法。现在，我可以使用

检测

，一切都很好。然而，为了满足我自己的好奇心，我尝试使用元编程显式地将

find

方法偷回一次运行：

unbound_method = [].method('find').unbind
unbound_method.bind(foo_instance.bars).call { ... }

我收到这个错误：

TypeError: bind argument must be an instance of Array

显然Ruby并不认为

foo_instance.bar

是一个数组，但：

foo_instance.bars.instance_of?(Array) -> true

有谁能帮我解释一下这一点，以及用元编程绕过它的方法吗

我想这是因为ActiveRecord 劫持了find方法以获取其 自己的目的

这不是真正的解释

foo_instance.bar

不返回数组的实例，而是返回

ActiveRecord:：Associations:：AssociationProxy

的实例。这是一个特殊的类，用于充当持有关联的对象和关联对象之间的代理

AssociationProxy对象充当数组，但它实际上不是数组。以下详细信息直接取自文档

# Association proxies in Active Record are middlemen between the object that
# holds the association, known as the <tt>@owner</tt>, and the actual associated
# object, known as the <tt>@target</tt>. The kind of association any proxy is
# about is available in <tt>@reflection</tt>. That's an instance of the class
# ActiveRecord::Reflection::AssociationReflection.
#
# For example, given
#
#   class Blog < ActiveRecord::Base
#     has_many :posts
#   end
#
#   blog = Blog.find(:first)
#
# the association proxy in <tt>blog.posts</tt> has the object in +blog+ as
# <tt>@owner</tt>, the collection of its posts as <tt>@target</tt>, and
# the <tt>@reflection</tt> object represents a <tt>:has_many</tt> macro.
#
# This class has most of the basic instance methods removed, and delegates
# unknown methods to <tt>@target</tt> via <tt>method_missing</tt>. As a
# corner case, it even removes the +class+ method and that's why you get
#
#   blog.posts.class # => Array
#
# though the object behind <tt>blog.posts</tt> is not an Array, but an
# ActiveRecord::Associations::HasManyAssociation.
#
# The <tt>@target</tt> object is not \loaded until needed. For example,
#
#   blog.posts.count
#
# is computed directly through SQL and does not trigger by itself the
# instantiation of the actual post records.

---

all

方法是ActiveRecordFinder方法（查找（：all）的快捷方式）。它返回结果的

数组。然后您可以在数组实例上调用
Array#find
方法。
ActiveRecord关联实际上是反射实例，它覆盖了的实例？和相关的方法来隐瞒它是什么类。这就是为什么您可以做一些事情，比如添加命名作用域（比如“最近”），然后调用foo_instance.bar.recent。如果“条”是一个数组，这将是相当棘手的

尝试签出源代码（“locate reflections.rb”应该可以在任何unix对话框中找到它）。查德·福勒（Chad Fowler）在这个话题上做了一次内容丰富的演讲，但我似乎在网上找不到任何链接。（有人想编辑这篇文章来包含一些吗？
正如其他人所说，关联对象实际上不是数组。要找出真正的类，请在irb中执行以下操作：

class << foo_instance.bars
  self
end
# => #<Class:#<ActiveRecord::Associations::HasManyAssociation:0x1704684>>

ActiveRecord::Associations::HasManyAssociation.ancestors
# => [ActiveRecord::Associations::HasManyAssociation, ActiveRecord::Associations::AssociationCollection, ActiveRecord::Associations::AssociationProxy, Object, Kernel]

类#
ActiveRecord:：Associations:：HasManyAssociation.Founders
#=>[ActiveRecord:：Associations:：HasManyAssociation，ActiveRecord:：Associations:：AssociationCollection，ActiveRecord:：Associations:：AssociationProxy，对象，内核]

要摆脱在执行foo_instance.bar.find（）时调用的ActiveRecord:：Bse#find方法，以下内容将有所帮助：

class << foo_instance.bars
  undef find
end
foo_instance.bars.find {...} # Array#find is now called

class这里要澄清的是，.all方法实际上检索所有关联的模型，这些模型可能会对内存产生巨大影响，具体取决于关联的类型。例如，如果是User has_many:posts，您可能正在检索用户的整个发布历史记录，这可能是大量数据。在可能的情况下，尝试构造一个带有条件或命名作用域的find调用，以获得更好的性能。
class << foo_instance.bars
  self
end
# => #<Class:#<ActiveRecord::Associations::HasManyAssociation:0x1704684>>

ActiveRecord::Associations::HasManyAssociation.ancestors
# => [ActiveRecord::Associations::HasManyAssociation, ActiveRecord::Associations::AssociationCollection, ActiveRecord::Associations::AssociationProxy, Object, Kernel]

class << foo_instance.bars
  undef find
end
foo_instance.bars.find {...} # Array#find is now called