Objectify optionally load referenced attributes

Question

I have a UserAccount that has a list of followings. This list of followings is saved as its own entity. I usually don't need the following list and, thus, I don't use @Load. However, I have a situation where I would like to load multiple UserAccounts together with their followings.

So, I need something like this:

OfyService.ofy().load().type(UserAccount.class).limit(200).loadReference("followerRef").list();

Example for the UserAccount:

@Entity
@Cache
public class UserAccount {
    @Id private String email;
    @Index
    private String nickname;
    private Ref<UserFollowing> followingRef;
}

elcid elcid · Accepted Answer · 2016-07-25T20:05:21

I believe Objectify already provides a way to do what you are after in the form of Load Groups. As you rightly pointed out using the @Load annotation will automatically retrieve a UserAccounts's followingRef which you don't want to happen for most cases.

In order to load a list of UserAccount with their followingRef you first have to apply the following simple modifications to your entity:

@Entity
public class UserAccount {
    public static class Everything {}

    @Id Long id;
    @Load(Everything.class) Ref<UserFollowing> followingRef;
}

You can then do the following to load a single UserAccount object:

// Doesn't load followingRef
UserAccount ua = ofy().load().key(userAccountKey).now();

// Does load followingRef
UserAccount ua = ofy().load().group(Everything.class).key(userAccountKey).now();

Similary you do this to load a list of UserAccount objects with their followinfRef:

// In your case you'd do something like
List<UserAccount> accounts = ofy().load()
                                  .type(UserAccount.class)
                                  .group(Everything.class)
                                  .list();

That should hopefully solve your problem. I don't know if that code compiles but if it doesn't shouldn't be too hard to fix.

For further reading click here and scroll down to Load Groups section

Objectify optionally load referenced attributes

1 Answers