CollectionProxy与AssociationRelation [英] CollectionProxy vs AssociationRelation

问题描述

我想知道 ActiveRecord :: Associations :: CollectionProxy 和 ActiveRecord :: AssociationRelation 之间的区别。 / p>

I am wondering about the difference between ActiveRecord::Associations::CollectionProxy and ActiveRecord::AssociationRelation.

class Vehicle < ActiveRecord::Base
  has_many :wheels
end

class Wheel < ActiveRecord::Base
  belongs_to :vehicle
end

我愿意：

v = Vehicle.new

v.wheels＃=> ＃< ActiveRecord :: Associations :: CollectionProxy []>

v.wheels.all＃=> ; ＃< ActiveRecord :: AssociationRelation []>

我不知道它们之间有什么区别，以及为什么以这种方式实现？

I have no idea what is the difference between them and why this is implemented this way?

推荐答案

ActiveRecord :: Relation 是简单的查询对象，在被打开之前进入查询并执行后， CollectionProxy 则稍微复杂一些。

ActiveRecord::Relation are simple query objects before being turned into a query and executed, CollectionProxy on the other hand are a little bit more sophisticated.

首先要获得关联范围，您可能会看到类似这样的情况，假设图书商店模型包含很多书籍

First of all you get association extentions, you probably saw something that looks like this, assume a book store model that has many books

class Store < ActiveRecord::Base
  has_many :books do
    def used
      where(is_used: true)
    end
  end
end

通过这种方式，您可以在商店中调用旧书

This way you get to call used books in a store using a syntax that looks like this

Store.first.books.used

但这是最基本的用法，您可以使用集合代理中公开的属性，这些属性是所有者，反射和目标

But this is the most basic uses, you could use the attributes that are exposed to you in the collection proxy, which are owner, reflection and target

所有者提供了对持有关联的父对象的引用

The owner provides a a reference to the parent object holding the association

reflection 对象是 ActiveRecord :: Reflection :: AssocciationReflection 的实例，并包含所有

The reflection object is an instance of ActiveRecord::Reflection::AssocciationReflection and contains all the configuration options for the association.

目标是关联集合对象（或单个o当 has_one 和属于时被拒绝。）

The target is the association collection objects (or single object when has_one and belongs_to).

使用这些您可以在关联范围内做一些处理的方法，例如，如果我们有一个博客，我们会将所有已删除帖子的访问权限授予管理员用户（我知道的例子是

Using those methods you could do some conditons in your association extention, for example if we have a blog, we give access to all deleted posts to users who are admins (lame example I know)

Class Publisher < ActiveRecord::Base
  has_many :posts do
    def deleted
      if owner.admin?
        Post.where(deleted: true)
      else
        where(deleted: true)
      end
    end
  end
end

您还可以使用另外两种方法，即 reset 和 reload ，第一个（ reset ）清除缓存的关联对象，第二个（ reload ）更为常见，它用于重置，然后从数据库中加载关联的对象。

You also get access to two more methods which are reset and reload, the first one (reset) clears the cached association objects, the second one (reload) is more common and is used to reset and then loads the associated objects from the database.

我希望这可以解释为什么拥有 CollectionProxy 类会如此有用

I hope this explains how having a CollectionProxy class would be so useful

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