title: accepts_nested_attributes_for whith json PUT (update)
body: <p>I have seen many examples of using accepts_nested_attributes_for but only a few of them for json POST/PUT and none of them helped me :/</p>
  
  <p>My application will be used to create forms.</p>
  
  <p>So, a form has many form_rows and a form_row can have many choices (in case it is a select of radio).
  So, I have my form model like this :</p>
  
  <pre><code>class Form &lt; ActiveRecord::Base
      attr_accessible :name
      has_many :form_rows
      accepts_nested_attributes_for :form_rows
  end
  </code></pre>
  
  <p>and my controller looks like this :</p>
  
  <pre><code>def update
      @form = Form.find(params[:id])
      @form.update_attributes!(params[:form])
  end
  </code></pre>
  
  <p>Here is the json I am trying to send</p>
  
  <pre><code>{
    "name": "form test 4",
    "form_rows_attributes": [
      {
        "domtype": "Input",
        "label": "Super row new"
      }
    ]
  }
  </code></pre>
  
  <p>In my scenario, the form creation only takes a name, it is after that that the user add the form_rows.</p>
  
  <p>When I do that, the name is correctly updated but the form_rows are not created at all. There is no error in my console, just the UPDATE for the form.</p>
  
  <p>What am I doing wrong?</p>