Ruby使用JSON序列化结构 [英] Ruby serialize struct with JSON

问题描述

我正在尝试将一个简单的结构序列化为可以正常工作的JSON，但是我无法从JSON中创建该结构的实例.这就是我试图做到的方式.

I am trying to serialize a simple struct to JSON which works fine, but I can't get it to create an instance of that struct from the JSON. Here is how I am trying to do it.

require 'rubygems'
require 'json'

Person = Struct.new(:name, :age)

json = Person.new('Adam', 19).to_json
puts json

me = JSON.load(json)
puts me.name

我得到以下输出:

"#<struct Person name=\"Adam\", age=19>"
/usr/lib/ruby/1.9.1/json/common.rb:148:in `parse': 746: unexpected token at '"#<struct Person name=\"Adam\", age=19>"' (JSON::ParserError)
    from /usr/lib/ruby/1.9.1/json/common.rb:148:in `parse'
    from /usr/lib/ruby/1.9.1/json/common.rb:309:in `load'
    from why.rb:9:in `<main>'

推荐答案

在这种情况下，person.to_json并没有达到您的期望.

In this case, person.to_json is not doing what you expect.

当您使用require 'json'时，JSON库会在Object上插入#to_json方法，如果其他地方没有提供专门的#to_json方法，则该方法会作为备用方法. 此插入的方法基本上是与在对象上调用#to_s#to_json相同.

When you require 'json', the JSON library inserts a #to_json method on Object that is a fallback if there's no specialized #to_json method provided elsewhere. This inserted method is basically the same as calling #to_s#to_json on an object.

对于这里的Person类，#to_s输出标准Object#to_s ，默认情况下，该标准不提供JSON库可解析的字符串.

In the case of your Person class here, #to_s outputs the standard Object#to_s, which, by default, doesn't provide a string parseable by the JSON library.

但是，Struct 确实提供了#to_h方法，可用于将该结构转换为Hash，并且Hash(根据需要JSON库)知道如何生成JSON可解析的输出.

However, Struct does provide a #to_h method that can be used to convert that struct to a Hash, and Hash is (upon requiring the JSON library) aware of how to generate a JSON parseable output.

因此只需更改:

json = Person.new('Adam', 19).to_json
puts json

收件人:

person = Person.new('Adam', 19)
puts person.to_h.to_json

将按照您的期望进行操作.

will do what you expect.

(顺便说一句，我实际上建议直接在Person类上实现#to_json，因为调用#to_h#to_json违反了法律特米特.)

(An aside, I would actually recommend implementing #to_json on the Person class directly as calling #to_h#to_json violates the Law of Demeter.)

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