Cannot Convert String and Fixnum to JSON in Rails 3

Question

    JSON.parse('abc'.to_json) gives this error (in rails):

    JSON::ParserError: 757: unexpected token at '"abc"'
    from /Users/mpapper/.rvm/gems/ruby-1.9.2-p290@dfc-site/gems/json-1.7.4/lib/json/common.rb:155:in `parse'
    from /Users/mpapper/.rvm/gems/ruby-1.9.2-p290@dfc-site/gems/json-1.7.4/lib/json/common.rb:155:in `parse'
    from (irb):20
    from /Users/mpapper/.rvm/gems/ruby-1.9.2-p290@dfc-site/gems/railties-3.1.3/lib/rails/commands/console.rb:45:in `start'
    from /Users/mpapper/.rvm/gems/ruby-1.9.2-p290@dfc-site/gems/railties-3.1.3/lib/rails/commands/console.rb:8:in `start'
    from /Users/mpapper/.rvm/gems/ruby-1.9.2-p290@dfc-site/gems/railties-3.1.3/lib/rails/commands.rb:40:in `<top (required)>'
    from script/rails:41:in `require'
    from script/rails:41:in `<main>'

Likewise this fails:

 JSON.parse(100.to_json)

And this too (with a slightly different error):

 JSON.parse(1.to_json)

Why dont I just wrap the outputted json in {} to make it look like real json? Because I'm writing code that should be able to take any object and serialize it as JSON and pull it back out again.

I think the issue comes from this: JSON looks like a set of encoded key-value pairs all put within {}. But the to_json methods in rails (3.x) don't output any {} at all.

Given that, all I really want is an easy way to serialize arbitrary ruby/rails objects into strings and back again. Already, many objects have a to_json method (String, Fixnum, Array, Hash) but the String and Fixnum versions don't produce Json that can be parsed.

Mark Bolusmjak · Accepted Answer · 2012-08-22 14:57:54Z

2

In the JSON RFC, we have the statement

A JSON text is a serialized object or array.

That pretty much sums it up. At the top level, your JSON must be one of array or object.

Can your code simply do something like:

json = {'myprotocol' => whatever}.to_json
result = JSON.parse(json)['myprotocol']

answered Aug 22, 2012 at 14:57

Mark Bolusmjak

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1 Comment

Mike P. Over a year ago

Thanks, that code works. Thus its up to my code to take the output of to_json and package it up nicely. Using ActiveSupport::JSON.decode as suggested by Serge is a much nicer way to do this (for me).

Serge Balyuk · Accepted Answer · 2012-08-22 15:03:47Z

1

It's not the JSON you're looking for. Try this:

ActiveSupport::JSON.decode('abc'.to_json)
ActiveSupport::JSON.decode(1.to_json)

edited Aug 22, 2012 at 15:03

answered Aug 22, 2012 at 14:53

Serge Balyuk

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