DropZone Help:
Step-1.
<form action="/projects/<%=current_project.try(:id)%>/uploads/dropzone_file_upload?recommendation_id=<%=recommendation.id%>" class="dropzone" id="demo-upload-<%=recommendation.id%>">
  <div class="dz-message needsclick">
    Drop files here or click to upload.<br />
  </div>
</form>            
<div id="preview-template" style="display: none;">
  <div class="dz-preview dz-file-preview">
    <div class="dz-image"><img data-dz-thumbnail /></div>
    <div class="dz-details">
      <div class="dz-size"><span data-dz-size></span></div>
      <div class="dz-filename"><span data-dz-name></span></div>              
    </div>
    <div class="dz-progress"><span class="dz-upload" data-dz-uploadprogress></span></div>
    <div class="dz-error-message"><span data-dz-errormessage></span></div>
  </div>
</div>
<script>
  dropzonSet("<%=recommendation.id%>");
</script>

Step-2.

var dropzonSet = function(recommendation_id){
  docsDropzone = new Dropzone( "#demo-upload-"+recommendation_id, {
  init: function() {
      this.on("complete", function (file) {
        data = JSON.parse(file.xhr.response)
        files=data.attachments>1 ? "Files" : "File"
        $("#attached_file_"+data.recommendation).html(data.attachments + " "+ files +" attached")
        html_remove_image =  "<a href='#' data-href='/uploads/dropzone_file_destroy?upload_id="+data.file+"&recommendation_id="+data.recommendation+"' class='remove-image remove-link-image' data-id='"+data.file+"'>X</a>"
        $(file.previewElement).prepend(html_remove_image)
        total_attachments = $($(".remove-image.remove-link-image").map(function(){return $(this).data("id")}).get()).size()
        file_count = total_attachments > 1 ? "Files" : "File"
        $("#img-attached_file").html(total_attachments + " " + file_count + " Attached");
      });
    }
  } );
}

Step-3.

respond_to do |format|
      format.json do
        render :json => {file: @file.id, recommendation: @recommendation.try(:id), attachments: @recommendation.try(:uploads).try(:size)}
      end
    end