在谷歌 appengine 上使用 django 使用数据初始化表单

Question

I have a post handler that uses a 'from google.appengine.ext.db.djangoforms.ModelForm'. It pulls the existing instance the data base then initialises the form by:

  myForm = TestForm(instance=self_instance, data=post_data)

I'm only putting one of the three properties in the post_data which is being correctly copied to the form but the other two properties which already have values in the 'self_instance' are being set to None. Can this be avoided?

Thanks, Richard

Answer 1

This is giving me the behaviour I'm after:

if self_instance:
  logging.info('creating form with instance so updating the post data, we need this to bind the form so we can validate it')
  if post_data:
    #update the post data with existing values
    for prop in self_instance._properties:
      if prop not in post_data:
        cur_prop_val = getattr(self_instance, prop)
        if isinstance(cur_prop_val,db.Model):
          str(cur_prop_val.key())
        else:
          post_data[prop] = cur_prop_val
  else:
    logging.info('no post data so not adding it to form')
  form_data = form_class(data=post_data,instance=self_instance)
else:
  logging.info('creating form without instance')
  form_data = form_class(data=post_data)  

Answer 2

You don't show your form definition. But, generally, if you don't want to include fields in the form, you should specify them in the Meta exclude tuple - then they won't be overwritten by non-existent POST data.

Answer 3

1. If you supply instance arg, the form is considered unbound
2. If you supply data arg, the form is considered bound

If you supply both, data will override instance (=> same as case 2, form bound).

So in your case, it's better to load self_instance then update it with data and then use the unbound form:

myForm = TestForm(instance=self_instance)