CODEWITHSUNDEEP
rubyjson
Blankman
Blankman

Reputation: 267190

Why isn't my ruby class converting to json?

I am confused why my simple ruby object is not converting to json.

>irb
>
require 'json'

class User
  attr_accessor :name, :age

  def initialize(name, age)
    @name = name
    @age = age
  end
end

u1 = User.new("a", 1)
u2 = User.new("b", 2)

puts u1.to_json
"\"#<User:0x000001010e9f78>\""

What am I missing?

I want to then store these objects into an array collection, and then convert the entire collection to json.

users = []
users << User.new("a", 1)
users << User.new("b", 2)

users.to_json

Note: This is not using Rails, just plain old Ruby!

I want my json to be an array of user objects.

[
{"name": "john", "age": 22},
{"name": "john1", "age": 23}
{"name": "john2", "age": 24}
]

Upvotes: 4

Views: 181

Answers (2)

Simone Carletti
Simone Carletti

Reputation: 176482

The default implementation of to_json is quite simple and clearly is not doing what you would expect. And this is expected: you need to write code to explain to the interpreter how you want your program to behave.

It's a common standard to provide both a to_json and as_json method. The first latter returns a JSON-serializable version of the instance (generally a Hash), the latter is the actual JSON output.

class User
  attr_accessor :name, :age

  def initialize(name, age)
    @name = name
    @age = age
  end

  def as_json(*)
    { name: @name, age: @age }
  end

  def to_json(*)
    as_json.to_json()
  end
end

Here's the output

2.3.0 :034 > u1.as_json
 => {:name=>"a", :age=>1}
2.3.0 :035 > puts u1.to_json
{"name":"a","age":1}
 => nil

With a little effort you can change the as_json to automatically collect all the instance variables. However, I discourage this approach as you may end-up serializing sensitive attributes you don't really want to share (like passwords).

Upvotes: 1

AMACB
AMACB

Reputation: 1298

By default, classes cannot be made into JSON strings. You must have a to_json method in your class, so you can make it inherit from this class (type class User < JSONable):

class JSONable
    def to_json
        hash = {}
        self.instance_variables.each do |x|
            hash[x] = self.instance_variable_get x
        end
        return hash.to_json
    end
end

Then, you can call to_json and it will work properly.

Test:

$ irb

irb(main):001:0> require 'json'
=> true
irb(main):002:0> class JSONable
irb(main):003:1>     def to_json
irb(main):004:2>         hash = {}
irb(main):005:2>         self.instance_variables.each do |x|
irb(main):006:3*             hash[x] = self.instance_variable_get x
irb(main):007:3>         end
irb(main):008:2>         return hash.to_json
irb(main):009:2>     end
irb(main):010:1> end
=> nil
irb(main):011:0> class User < JSONable
irb(main):012:1>  attr_accessor :name, :age
irb(main):013:1> 
irb(main):014:1*   def initialize(name, age)
irb(main):015:2>     @name = name
irb(main):016:2>     @age = age
irb(main):017:2>   end
irb(main):018:1> end
=> nil
irb(main):019:0> 
irb(main):020:0* user = User.new("hi",3)
=> #<User:0x007fd6c8af0a90 @name="hi", @age=3>
irb(main):021:0> puts user.to_json
{"@name":"hi","@age":3}

Upvotes: 0

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