将虚拟属性添加到 json 输出 [英] Add virtual attribute to json output

问题描述

假设我有一个处理待办事项列表的应用程序.清单有已完成和未完成的项目.现在我想向列表对象添加两个虚拟属性；列表中已完成和未完成项目的数量.我还需要将这些显示在 json 输出中.

Let's say I have an app that handles a TODO list. The list has finished and unfinished items. Now I want to add two virtual attributes to the list object; the count of finished and unfinished items in the list. I also need these to be displayed in the json output.

我的模型中有两种方法可以获取未完成/已完成的项目:

I have two methods in my model which fetches the unfinished/finished items:

def unfinished_items 
  self.items.where("status = ?", false) 
end 

def finished_items 
  self.items.where("status = ?", true) 
end

那么，如何在我的 json 输出中获取这两种方法的数量?

So, how can I get the count of these two methods in my json output?

我使用的是 Rails 3.1

I'm using Rails 3.1

推荐答案

Rails中对象的序列化有两个步骤:

The serialization of objects in Rails has two steps:

• 首先，调用 as_json 将对象转换为简化的 Hash.
• 然后，在 as_json 返回值上调用 to_json 以获得最终的 JSON 字符串.

• First, as_json is called to convert the object to a simplified Hash.
• Then, to_json is called on the as_json return value to get the final JSON string.

您通常希望单独保留 to_json，因此您需要做的就是添加 你自己的as_json 实现 有点像这样:

You generally want to leave to_json alone so all you need to do is add your own as_json implementation sort of like this:

def as_json(options = { })
  # just in case someone says as_json(nil) and bypasses
  # our default...
  super((options || { }).merge({
    :methods => [:finished_items, :unfinished_items]
  }))
end

你也可以这样做:

def as_json(options = { })
  h = super(options)
  h[:finished]   = finished_items
  h[:unfinished] = unfinished_items
  h
end

如果您想为方法支持的值使用不同的名称.

if you wanted to use different names for the method-backed values.

如果您关心 XML 和 JSON，请查看 serializable_hash.

If you care about XML and JSON, have a look at serializable_hash.

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