to_json of hash containing an array

Hi there,

I am fairly new to the Rails framework, so forgive me if there is an
obvious solution to this problem.

I am using Rails 2.1.0 and trying to jsonify a hash containing an
array. E.g.

result = { :name => "McLovin", :attachments => ['file.pdf', 'file.jpg'] }

=> {:attachments=>["file.pdf", "file.jpg"], :name=>"McLovin"}

result.to_json

I would expect something like:

{
    "name": "McLovin",
    "attachments": [
        "file.pdf",
        "file.jpg"
    ]
}

But instead I get:

TypeError: wrong argument type Hash (expected Data)
  from /Library/Ruby/Gems/1.8/gems/activesupport-2.1.0/lib/
active_support/json/encoding.rb:21:in `to_json'
  from /Library/Ruby/Gems/1.8/gems/activesupport-2.1.0/lib/
active_support/json/encoding.rb:21:in `send'
  from /Library/Ruby/Gems/1.8/gems/activesupport-2.1.0/lib/
active_support/json/encoding.rb:21:in `encode'
  from /Library/Ruby/Gems/1.8/gems/activesupport-2.1.0/lib/
active_support/json/encoding.rb:31:in `raise_on_circular_reference'
  from /Library/Ruby/Gems/1.8/gems/activesupport-2.1.0/lib/
active_support/json/encoding.rb:20:in `encode'
  from /Library/Ruby/Gems/1.8/gems/activesupport-2.1.0/lib/
active_support/json/encoders/hash.rb:42:in `to_json'
  from /Library/Ruby/Gems/1.8/gems/activesupport-2.1.0/lib/
active_support/json/encoders/hash.rb:41:in `map'
  from /Library/Ruby/Gems/1.8/gems/activesupport-2.1.0/lib/
active_support/json/encoders/hash.rb:41:in `to_json'
  from /Library/Ruby/Gems/1.8/gems/activesupport-2.1.0/lib/
active_support/core_ext/object/misc.rb:28:in `returning'
  from /Library/Ruby/Gems/1.8/gems/activesupport-2.1.0/lib/
active_support/json/encoders/hash.rb:40:in `to_json'
  from (irb):54

If I do "result.to_json( :except => :attachments )", then it works.

Best regards, Mads Kristiansen