How to get a list of key names in Python/Google app engine?

In Python/Google app engine, I'd like to store a property as a key name in order to save resources and speed things up. But I don't know how to get the list of key names.

As an example, consider the data model:

class Book(db.Model):
    isbn = db.StringProperty() # Make this a key name instead.
    category = db.StringProperty()
    author = db.StringProperty()
    title = db.StringProperty()
    ...

Now let's say I set the key name to the isbn instead of making it a property name:

new_book = Book(category="fantasy,comedy", title="The Light Fantastic", author="Terry Pratchett", key_name=isbn_number)

I guess that, if I could find a way of getting a list of key names, I would save resources? For example, when ch开发者_StackOverflow社区ecking if a particular book is already in the collection.

Is this correct, and how do I get a list of key names?

If this isn't the case, then would the following be a decent compromise:

class ISBN(db.Model):
    isbn = db.StringProperty()

class Book(db.Model):
    isbn = db.ReferenceProperty(ISBN)
    category = db.StringProperty()
    author = db.StringProperty()
    title = db.StringProperty()
    ...  

Would it save resources/be faster?

For the first approach, ISBN as key:

class Book(db.Model):
    #isbn is key, so it shouldn't be a property
    category = db.StringProperty()
    author = db.StringProperty()
    title = db.StringProperty()

new_book = Book(category="fantasy,comedy", title="The Light Fantastic", author="TerryPratchett", key_name=isbn_number)

Then getting list of all ISBNs:

isbns = [b.name() for Book.all(keys_only=True)]

Creating a Book

b = Book(key_name='isbn:0134815100494', **props)
b.put()

Querying

keys = Book.all(keys_only=True).fetch(100)
key_names = [key.name() for key in keys]

Look for keys_only and key_name when searching

You don't need a list of key names for your use case.

If you want to see if a book is already in the database, simply do Book.get_by_key_name(someISBN). There's also get_or_insert for writes, which will check if the entity you're adding is already in the database, writing it if it's not and returning it if it is.