How To Check If Ndb Model Is Valid

I have a model class like: class Book(ndb.Model): title = ndb.StringProperty(required=True) author = ndb.StringProperty(required=True) and I have some code using this:

Solution 1:

The approach below does not work! I run into problems later on. I cannot recall right now what is was.

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I have not found an "official" way of doing this. This is my workaround:

classCredentials(ndb.Model):
    """
    Login credentials for a bank account.
    """
    username = ndb.StringProperty(required=True)
    password = ndb.StringProperty(required=True)

    def__init__(self, *args, **kwds):
        super(Credentials, self).__init__(*args, **kwds)
        self._validate()   # call my own validation here!def_validate(self):
        """
        Validate all properties and your own model.
        """for name, prop in self._properties.iteritems():
            value = getattr(self, name, None)
            prop._do_validate(value)
        # Do you own validations at the model level below.

Overload __init__ to call my own _validate function. There I call _do_validate for each property, and eventually a model level validation.

There is a bug opened for this: issue 177.

Solution 2:

The model is valid, but you have specified that both title and author are required. So you have to provide values for these properties every time you write something in. Basically you are trying to write an empty record.

try:

book = Book()
title = "Programming Google App Engine"author = "Dan Sanderson"book_key = book.put()

Solution 3:

You could try using the validation method that NDB itself uses when it raises the BadValueError.

book = Book()
book._check_initialized()

This will raise the BadValueError like when you try to put the entry into the datastore.