Question

I was reading the GAE documentation for NDB data storing on this page.

https://developers.google.com/appengine/docs/python/ndb/overview#storing

In the following code,

greeting = Greeting(parent=ndb.Key("Book", guestbook_name or "*notitle*"),
                    content = self.request.get('content'))

Greeting has a Key set as it’s parent. Besides, that Key is constructed with a “Book” string which seems like just a random string.

Does Key class constructor accepts a random string for kind parameter?

Thank you.

Answer 1

When you set a parent it does not actually have to exist.

So yes, in a way it’s a random string. But if you had a model called Book

class Book(ndb.Model):
  content = ndb.StringProperty()

That could have been written like this:

greeting = Greeting(parent=ndb.Key(Book, guestbook_name or "*notitle*"),
                    content = self.request.get('content'))

The docs note:

Alternatively, you can use the model class object itself, rather than its name, to specify the entity’s kind

Which is what I did here. Both amount to the same thing.