# To\_json of hash containing an array

**URL:** <https://www.ruby-forum.com/t/to-json-of-hash-containing-an-array/146720>\
**Category:** Rails\
**Created:** [August 24, 2008, 7:28pm UTC](https://www.ruby-forum.com/t/to-json-of-hash-containing-an-array/146720 "2008-08-24T19:28:52Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Mads\_K](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/54ee81/32.png) [@Mads\_K](https://www.ruby-forum.com/u/Mads_K)\
**Post date:** [August 24, 2008, 7:28pm UTC](https://www.ruby-forum.com/t/to-json-of-hash-containing-an-array/146720/1 "2008-08-24T19:28:52Z")

</div>

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 K.