from json to a ruby hash?

Question

I can go one way using

require 'json'

def saveUserLib(user_lib)
    File.open("/Users/name/Documents/user_lib.json","w") do |f|
    f.write($user_lib.to_json)
    end
end

uname = gets.chomp
$user_lib["_uname"] = uname
saveUserLib($user_lib)

but how do i get it back again as my user_lib?

Small code criticism: you should not hardcode the file path into your method. You should either have your method accept a file path, or put a constant at the top of your file with the path to use. Rule of thumb (there are always exceptions): if you ever hard code a number (other than perhaps 1) or user-facing string inside a method, you're making your code more fragile and harder to maintain. — Phrogz, Jan 29 '12 at 17:57
when I remove my `$`'s I get the following error: `
': undefined local variable or method `user_lib' for main:Object (NameError) — beoliver, Jan 29 '12 at 18:07
but about the path - this i am aware - but it was for a quick test! thanks for the heads up though — beoliver, Jan 29 '12 at 18:10

Phrogz · Accepted Answer · 2016-04-12T20:13:28.670

97

You want JSON.parse or JSON.load:

def load_user_lib( filename )
  JSON.parse( IO.read(filename) )
end

The key here is to use IO.read as a simple way to load the JSON string from disk, so that it can be parsed. Or, if you have UTF-8 data in your file:

  my_object = JSON.parse( IO.read(filename, encoding:'utf-8') )

I've linked to the JSON documentation above, so you should go read that for more details. But in summary:

json = my_object.to_json — method on the specific object to create a JSON string.
json = JSON.generate(my_object) — create JSON string from object.
JSON.dump(my_object, someIO) — create a JSON string and write to a file.
my_object = JSON.parse(json) — create a Ruby object from a JSON string.
my_object = JSON.load(someIO) — create a Ruby object from a file.

Alternatively:

def load_user_lib( filename )
  File.open( filename, "r" ) do |f|
    JSON.load( f )
  end
end

Note: I have used a "snake_case" name for the method corresponding to your "camelCase" saveUserLib as this is the Ruby convention.

edited Apr 12 '16 at 20:13

answered Jan 29 '12 at 17:29

Phrogz

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what is the difference between `JSON.dump` / `.to_json` / `JSON.generate` and then `JSON.parse` / `JSON.load` ? – beoliver Jan 29 '12 at 17:35
@user969617 I've edited my answer to show the difference, and summarize the ways of dealing with JSON data. – Phrogz Jan 29 '12 at 17:48
Both `JSON.parse` and `JSON.load` can "create a Ruby object from a JSON string" – pje Aug 30 '12 at 13:17
1

As this is the top answer, I think you should correct the JSON.parse call to `JSON.parse(IO.read(filename))` – mwallisch Mar 10 '13 at 20:57
@walfish3d But of course, and thanks. (You're also welcome in the future to edit someone else's answer when such an obvious mistake has been made. ;) – Phrogz Mar 11 '13 at 02:40
3

Contrary to what you may expect, you get stuff like `user['name']` not `user[:name]` – ashes999 Apr 16 '14 at 01:15

alexkv · Answer 2 · 2012-01-29T18:18:50.170

2

here is some example:

require 'json'

source_hash = {s: 12, f: 43}
json_string = JSON.generate source_hash
back_to_hash = JSON.parse json_string

edited Jan 29 '12 at 18:18

answered Jan 29 '12 at 17:26

alexkv

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Not true! `JSON.parse` result is string-full as `{"s"=>12, "f"=>43}` not `{s: 12, f: 43}` – S.M.Mousavi Nov 17 '12 at 14:40

score 2 · Answer 3 · edited Jan 29 '12 at 17:31

2

JSON.load will do the trick. Here's an example that goes both ways:

>> require 'json'
=> true
>> a = {"1" => "2"}
=> {"1"=>"2"}
>> b = JSON.dump(a)
=> "{\"1\":\"2\"}"
>> c = JSON.load(b)
=> {"1"=>"2"}

edited Jan 29 '12 at 17:31

Ken Bloom

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answered Jan 29 '12 at 17:28

Chris Bunch

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from json to a ruby hash?

3 Answers3

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