Collapsing multiple trips to the datastore into a single trip?

Question

Hi,

Is there a way to merge multiple trips to the datastore into one trip? I have something like this:

class User {
    @PrimaryKey
    private String mUsername;
}

class Horse {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key mKey;

    @Persistent
    private String mOwnerUsername;
}

class Cow {
    @PrimaryKey
    @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
    private Key mKey;

    @Persistent
    private String mOwnerUsername;
}

A User can own many Horses or Cows. Right now to get all of a user's horses and cows, I'm making three separate trips to the datastore with three separate queries, something like:

User user = select from Users where userid = 'abc';
List<Horse> horses = select from Horses where ownerUsername = 'abc';
List<Cow> cows = select from Cows where ownerUsername = 'abc';

is there a way to collapse those three into a single trip to the datastore? I don't want to make the horses and cows members of the User class, because there may be a huge number of them, and don't want to load them on every load of User. Also a User does not have sole ownership of a horse or cow, they can be owned by many different entities.

Thanks

Answer 1

If you use key names, you can make the first query into a fetch by key operation, which is faster. If you're using a framework other than JDO, you can group multiple fetch by key operations into one roundtrip.

You can't, however, collapse multiple queries into a single request, nor can you (currently) do asynchronous requests.