Rails not decoding JSON from jQuery correctly (array becoming a hash with integer keys)

Question

Every time I want to POST an array of JSON objects with jQuery to Rails, I have this problem. If I stringify the array I can see that jQuery is doing its work correctly:

"shared_items"=>"[{\"entity_id\":\"253\",\"position\":1},{\"entity_id\":\"823\",\"position\":2}]"

But if I just send the array it as the data of the AJAX call I get:

"shared_items"=>{"0"=>{"entity_id"=>"253", "position"=>"1"}, "1"=>{"entity_id"=>"823", "position"=>"2"}}

Whereas if I just send a plain array it works:

"shared_items"=>["entity_253"]

Why is Rails changing the array to that strange hash? The only reason that comes to mind is that Rails can't correctly understand the contents because there is no type here (is there a way to set it in the jQuery call?):

Processing by SharedListsController#create as 

Thank you!

Update: I'm sending the data as an array, not a string and the array is created dynamically using the .push() function. Tried with $.post and $.ajax, same result.

Answer 1

In case someone stumbles upon this and wants a better solution, you can specify the "contentType: 'application/json'" option in the .ajax call and have Rails properly parse the JSON object without garbling it into integer-keyed hashes with all-string values.

So, to summarize, my problem was that this:

$.ajax({
  type : "POST",
  url :  'http://localhost:3001/plugin/bulk_import/',
  dataType: 'json',
  data : {"shared_items": [{"entity_id":"253","position":1}, {"entity_id":"823","position":2}]}
});

resulted in Rails parsing things as:

Parameters: {"shared_items"=>{"0"=>{"entity_id"=>"253", "position"=>"1"}, "1"=>{"entity_id"=>"823", "position"=>"2"}}}

whereas this (NOTE: we're now stringifying the javascript object and specifying a content type, so rails will know how to parse our string):

$.ajax({
  type : "POST",
  url :  'http://localhost:3001/plugin/bulk_import/',
  dataType: 'json',
  contentType: 'application/json',
  data : JSON.stringify({"shared_items": [{"entity_id":"253","position":1}, {"entity_id":"823","position":2}]})
});

results in a nice object in Rails:

Parameters: {"shared_items"=>[{"entity_id"=>"253", "position"=>1}, {"entity_id"=>"823", "position"=>2}]}

This works for me in Rails 3, on Ruby 1.9.3.