old_contents: from google.appengine.ext.db import djangoforms
  from charter.models import Chart
  
  class ChartForm(djangoforms.ModelForm):
      class Meta:
          model = Chart
  
new_contents: from google.appengine.ext.db import djangoforms
  from charter.models import Chart
  
  class ChartForm(djangoforms.ModelForm):
      class Meta:
          model = Chart
          exclude = ('data', 'user', 'hash',)
  
subject: remove fields which should be autopopulated