Handling JSON in JS/ERB template in Rails 3

Question

I have no trouble making typical AJAX calls to and from Rails(3) with JSON objects and jQuery-rails (jQuery library plus a special rails.js file).

In one controller, though, I want to RETURN some JSON in an erb template (create.js.erb) after an AJAX call.

I've tried every combination of things in the controller (@object.to_json, '[{"content":"hello world"}]', etc.) and in the template itself (JSON.parse(), single quotes, double quotes, etc.), but the object keeps on rendering like this:

'[{"groups":{},"created_at":"2010-09-21T03:49:34Z" ...

and as a result, my jQuery code cannot parse it and I get errors.

How do I need to prep my object in the controller, and what erb syntax do I need in the view for it to render as a valid JSON object?

Thanks so much!

Answer 1

I'm not sure this is the cause, but you can also try playing around with html_safe method. ERB might be escaping your JSON because it thinks it's not html safe. Try calling that method when using the string:

@object.to_json.html_safe

Answer 2

Using html_escape or raw alone will leave you vulnerable to XSS.

Instead, define a sensible version of the json_escape (a.k.a. j) helper:

module ActionView::Base
  def json_escape(s)
    result = s.to_s.gsub('/', '\/')
    s.html_safe? ? result.html_safe : result
  end

  alias j json_escape
end

Use it like this:

<script>
  var Accounts = new Backbone.Collection;
  Accounts.reset(<%=j @accounts.to_json.html_safe %>);
  var Projects = new Backbone.Collection;
  Projects.reset(<%=j @projects.to_json(:collaborators => true).html_safe %>);
</script>

See this post for further details.

Be aware that there's a naming conflict between j aliased to json_escape in ERB::Util and j aliased to escape_javascript in ActionView::Helpers::JavaScriptHelper. It's my hope that the JavaScriptHelper alias will be renamed to js.

Answer 3

To return json you have to write your render in the controller as follows:

render :json => @object

and the .to_json will automatically be called.

If you would want to include some relations, you could do the following:

render :json => @post.to_json(:include => [:comments, :authors])

I am not sure if it would work to use an erb to render your json.