Question

I’m using the Handsontable jquery plugin to change cells in a datagrid. Handsontable sends the data in an array as such:

var change = [['Z', null, 'X']]

I then pass this data to the server using ajax:

$.ajax({
  url: "/incomes",
  dataType: "text",
  type: "POST",
  data: { data: change },
});

The problem is that with a null value ajax will ignore this value and change the array, like such:

change[0][0]    Z
change[0][1]    
change[0][2]    X

Because this value in the array is null, Webrick throws the following error:
Internal Server Error
expected Hash (got Array) for param 0

I’m really hoping to avoid looping through the data (there are multiple arrays in a real example) and changing any of these null values. Is there an easier way to ensure that data can be sent to the server without erring out?

HTML Error:

Internal Server Error

expected Hash (got Array) for param `0′

---

WEBrick/1.3.1 (Ruby/1.9.3/2012-11-10) at
localhost:3000

Terminal Error:

ERROR TypeError: expected Hash (got Array) for param `0'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/rack-1.4.4/lib/rack/utils.rb:127:in `normalize_params'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/rack-1.4.4/lib/rack/utils.rb:128:in `normalize_params'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/rack-1.4.4/lib/rack/utils.rb:96:in `block in parse_nested_query'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/rack-1.4.4/lib/rack/utils.rb:93:in `each'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/rack-1.4.4/lib/rack/utils.rb:93:in `parse_nested_query'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/rack-1.4.4/lib/rack/request.rb:332:in `parse_query'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/rack-1.4.4/lib/rack/request.rb:209:in `POST'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/rack-1.4.4/lib/rack/methodoverride.rb:26:in `method_override'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/rack-1.4.4/lib/rack/methodoverride.rb:14:in `call'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/rack-1.4.4/lib/rack/runtime.rb:17:in `call'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/activesupport-3.2.9/lib/active_support/cache/strategy/local_cache.rb:72:in `call'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/rack-1.4.4/lib/rack/lock.rb:15:in `call'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/actionpack-3.2.9/lib/action_dispatch/middleware/static.rb:62:in `call'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/railties-3.2.9/lib/rails/engine.rb:479:in `call'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/railties-3.2.9/lib/rails/application.rb:223:in `call'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/rack-1.4.4/lib/rack/content_length.rb:14:in `call'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/railties-3.2.9/lib/rails/rack/log_tailer.rb:17:in `call'
    /home/g/.rvm/gems/ruby-1.9.3-p327/gems/rack-1.4.4/lib/rack/handler/webrick.rb:59:in `service'
    /home/g/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
    /home/g/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
    /home/g/.rvm/rubies/ruby-1.9.3-p327/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'

Answer 1

This is a stab in the dark, but you might try doing your POST with JSON or some other content type:

$.ajax({
  url: "/incomes",
  dataType: "text",
  type: "POST",
  data: JSON.stringify({ data: change }),
  contentType: 'application/json'
});

I suggest this as a solution because the JSON format can represent null values and nested arrays more naturally (IMO) than the default x-www-form-urlencoded format.

How this Works

JSON.stringify will make sure your data are serialized as JSON. Using the contentType setting like this will cause the Content-Type header to ‘application/json’ in the HTTP request. Rails uses this as a clue to interpret the incoming POST body as JSON.