/*
* LensKit, an open source recommender systems toolkit.
* Copyright 2010-2014 LensKit Contributors. See CONTRIBUTORS.md.
* Work on LensKit has been funded by the National Science Foundation under
* grants IIS 05-34939, 08-08692, 08-12148, and 10-17697.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
* FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
* details.
*
* You should have received a copy of the GNU General Public License along with
* this program; if not, write to the Free Software Foundation, Inc., 51
* Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
package org.grouplens.lenskit.data.dao;
import com.google.common.base.Function;
import com.google.common.base.Supplier;
import com.google.common.base.Suppliers;
import it.unimi.dsi.fastutil.longs.LongOpenHashSet;
import it.unimi.dsi.fastutil.longs.LongSet;
import org.grouplens.lenskit.cursors.Cursor;
import org.grouplens.lenskit.data.event.Event;
import org.grouplens.lenskit.util.io.Describable;
import org.grouplens.lenskit.util.io.DescriptionWriter;
import javax.annotation.Nullable;
import javax.inject.Inject;
/**
* User DAO that streams the events to get user information. The user set is fetched and memorized
* once for each instance of this class.
*
* @since 2.0
* @author <a href="http://www.grouplens.org">GroupLens Research</a>
*/
public final class PrefetchingUserDAO implements UserDAO, Describable {
private final EventDAO eventDAO;
private final Supplier<LongSet> userCache;
/**
* A function that wraps an event DAO in a prefetching user DAO. If the DAO already
* implements {@link UserDAO}, it is returned unwrapped.
* @return A wrapper function to make user DAOs from event DAOs.
*/
public static Function<EventDAO,UserDAO> wrapper() {
return WrapperFunction.INSTANCE;
}
private static enum WrapperFunction implements Function<EventDAO,UserDAO> {
INSTANCE;
@Nullable
@Override
public UserDAO apply(@Nullable EventDAO input) {
if (input instanceof UserDAO) {
return (UserDAO) input;
} else {
return new PrefetchingUserDAO(input);
}
}
}
@Inject
public PrefetchingUserDAO(EventDAO events) {
eventDAO = events;
userCache = Suppliers.memoize(new UserScanner());
}
@Override
public LongSet getUserIds() {
return userCache.get();
}
@Override
public void describeTo(DescriptionWriter writer) {
writer.putField("daoType", "User")
.putField("delegate", eventDAO);
}
private class UserScanner implements Supplier<LongSet> {
@Override
public LongSet get() {
LongSet us = new LongOpenHashSet();
Cursor<Event> events = eventDAO.streamEvents();
try {
for (Event e: events) {
us.add(e.getUserId());
}
} finally {
events.close();
}
return us;
}
}
}