Optional reference field in app engine datastore

Question

I have a model

class MyModel(ndb.Model):
    foo = ndb.StringProperty()

class OtherModel(ndb.Model):
    baz = ndb.StringProperty()
    ref = ndb.KeyProperty(kind=MyModel)

I built a view where I can create and modify these model entities and I would like the ref field of OtherModel to be optional but when I try to submit and empty ref field or remove the old value of it I got an error of the ndb.KeyProperty's validation

My updating logic looks like this:

for property in editableProperties:
    # Lets suppose this parses values from a form in a request to the needed type
    new_value = deserialize(property._kind, self.request.get(property._name))
    setattr(item, property._name, new_value)

Where I tried setting the new_value to None and empty string. How can I make possible to do this?

Answer 1

If you don't have a Model entity key to set the ref property to just do not set it - i.e. do not include that property in the entity value that you're passing back to the datastore for writing. If you do, the property value you're passing will be subjected to sanity checks and they'll fail.

In other words: do not do at all

`setattr(item, property._name, new_value)`

for ref when new_value is not a key. Instead do something along these lines:

if hasattr(item, property._name):
   delattr(item, property._name)