Q:

objectify query by keys

I have an Entity as
@Entity
public class Book{
  ...
  List<Key<Page>> pages;
  ...
}

So to get a book I do
Book book = ofy().load().type(Book.class).id(id).now();

Having obtained the book, I want to get the pages; hence my question: can I query by keys or must I query by ids? If I had the ids I could do
List<Page> pages = ofy().load().type(Page.class).ids(ids);

But what I need is
List<Page> pages = ofy().load().type(Page.class).keys(keys);

otherwise I have to do linear work to iterate through the keys to extract the ids or the names, which I am not even sure will work because the keys actually have parents so that a key for a page is constructed as
Key pageKey = KeyFactory.createKey(bookKey, Page.class.getSimpleName(),someString);

So what is my final answer in this case?

A:

You can easily load entities by Keys. From ofy's Concepts page (https://code.google.com/p/objectify-appengine/wiki/Concepts) 
Map<Key<Object>, Object> lotsOfThings = ofy().load().keys(carKey, airplaneKey, chairKey, personKey, yourMamaKey);

