When do you register classes in Objectify for GAE?

Question

So this might be kind of a dumb question but when do you register classes with:

ObjectifyService.register( User.class );

Currently, I'm doing this in the constructor of an interface-like class that I use in my other classes to simplify usage of the Data store specifically to my application. However, I'm getting this error:

Attempted to register kind 'User' twice

So, I guess my question is how often and specifically when do you register classes in Objectify?

Thanks!

P.S. Here's my entire class:

import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.Iterator;

import javax.crypto.BadPaddingException;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.persistence.Id;

import com.googlecode.objectify.Objectify;
import com.googlecode.objectify.ObjectifyService;
import com.googlecode.objectify.annotation.Indexed;
import com.googlecode.objectify.annotation.Unindexed;

public class UsersService {

    Objectify ojy;

    public UsersService(){
        ObjectifyService.register( User.class );
        ojy = ObjectifyService.begin();
    }

    public void regUser(String email, String password, String firstName, String lastName){
        //TODO: Check syntax if email
        //TODO: store encrypted password
    }

    public void regUser(String email, String password, String firstName){
        regUser(email, password, firstName, null);
    }

    public void regUser(String email, String password){
        regUser(email, password, "", "");
    }

    public boolean checkFor(Long acc_id){
        User checked_user = ojy.find(User.class, acc_id);
        if(checked_user == null){
            return false;
        }else{
            return true;
        }
    }

    public User getUser(String email, String password) throws InvalidKeyException, IllegalBlockSizeException, BadPaddingException, NoSuchAlgorithmException, NoSuchPaddingException{
        String pass_enc = MyUtils.getEncrypted(password);
        Iterable<User> users = ojy.query(User.class).filter("email", email).filter("password", pass_enc);
        Iterator<User> iter = users.iterator();
        if(iter.hasNext()){
            return iter.next();
        }else{
            return null;
        }
    }

}

Answer 1

Update

Here is the Best Practice Solution:

Use Your Own Service , This guarantees that your entities are registered before you use Objectify, but doesn't necessarily impact application startup for requests which do not access the datastore.

import com.googlecode.objectify.Objectify;
import com.googlecode.objectify.ObjectifyFactory;
import com.googlecode.objectify.ObjectifyService;


public class OfyService {
    static {
        ObjectifyService.register(User.class);
    }

    public static Objectify ofy() {
        return ObjectifyService.begin();//prior to v.4.0 use .begin() , 
                                        //since v.4.0  use ObjectifyService.ofy();
    }

    public static ObjectifyFactory factory() {
        return ObjectifyService.factory();
    }

}

Then use it like this:

public User createUser(User pUser) {

    Objectify objectify = OfyService.ofy();
    objectify.put(pUser);

    return pUser;
}

---

Original Answer (better use the code above):

you should do it this way in your class, just put a static block like this:

static{
    ObjectifyService.register( User.class );
}

p.s , you take a look at the best practice of objectify too

http://code.google.com/p/objectify-appengine/wiki/BestPractices

Answer 2

Based on Danie's answer and in case someone else is using dependency injection I did this for Spring MVC and worked perfect:

I created a service as follows:

@Service
@Qualifier("objectifyService")
public class OfyService {
    static {
        ObjectifyService.register(GaeUser.class);
    }

    public static Objectify ofy() {
        return ObjectifyService.ofy();
    }

    public static ObjectifyFactory factory() {
        return ObjectifyService.factory();
    }

}

Then whenever I want to use it I just inject the service like this:

@Autowired
@Qualifier("objectifyService")
OfyService objectifyService;

And then I use it like this:

objectifyService.ofy().save().entity(user).now();

Answer 3

I use the @Entity annotation, the Reflections library and runtime registration with no significant impact in start up time of any of my applications because all the information is collected at compile/build time.

ObjectifyLoaderContextListener.java

package com.vertigrated.servlet;

import com.google.appengine.api.ThreadManager;
import com.googlecode.objectify.ObjectifyFactory;
import com.googlecode.objectify.ObjectifyService;
import com.googlecode.objectify.annotation.Entity;
import org.reflections.Reflections;
import org.reflections.util.ClasspathHelper;
import org.reflections.util.ConfigurationBuilder;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.annotation.Nonnull;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * This class processes the classpath for classes with the @Entity or @Subclass annotations from Objectify
 * and registers them with the ObjectifyFactory, it is multi-threaded uses a prebuilt list of classes to process
 * created by the Reflections library at compile time and works very fast!
 */
public class ObjectifyLoaderContextListener implements ServletContextListener
{
    private static final Logger L = LoggerFactory.getLogger(ObjectifyLoaderContextListener.class);

    private final Set<Class<?>> entities;

    public ObjectifyLoaderContextListener()
    {
        this.entities = new HashSet<>();
    }

    @Override
    public void contextInitialized(@Nonnull final ServletContextEvent sce)
    {
        final ConfigurationBuilder cb = new ConfigurationBuilder();
        cb.setUrls(ClasspathHelper.forPackage(""));
        final ExecutorService es = Executors.newCachedThreadPool(ThreadManager.currentRequestThreadFactory());
        cb.setExecutorService(es);
        final Reflections r = new Reflections(cb);
        this.entities.addAll(r.getTypesAnnotatedWith(Entity.class));
        es.shutdown();
        final ObjectifyFactory of = ObjectifyService.factory();
        for (final Class<?> cls : this.entities)
        {
            of.register(cls);
            L.debug("Registered {} with Objectify", cls.getName());
        }
    }

    @Override
    public void contextDestroyed(@Nonnull final ServletContextEvent sce)
    {
        /* this is intentionally empty */
    }
}