net.sf.derquinsej.hib3.seq.SequenceDAO.java Source code

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Here is the source code for net.sf.derquinsej.hib3.seq.SequenceDAO.java

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/*
 * Copyright 2007 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package net.sf.derquinsej.hib3.seq;

import org.hibernate.LockOptions;
import org.hibernate.Session;
import org.hibernate.SessionFactory;

import com.google.common.base.Preconditions;

/**
 * Data access object for the sequence entity. As it represents a very specific case, it does not
 * follow normal best-practices (interface-based, etc.). WARNING: Transactional sequences are a
 * source of locks and may hurt scalability.
 * @author Andres Rodriguez
 */
public class SequenceDAO {
    /** Hibernate Session factory. */
    private final SessionFactory sessionFactory;

    /**
     * Initialized the DAO
     * @param sessionFactory Hibernate Session factory.
     */
    public SequenceDAO(final SessionFactory sessionFactory) {
        this.sessionFactory = Preconditions.checkNotNull(sessionFactory, "The session factory is mandatory.");
    }

    private static String nonNull(String id) {
        return Preconditions.checkNotNull(id, "The sequence name (id) is mandatory.");
    }

    /**
     * Gets the current value of a sequence.
     * @param id Sequence name.
     * @return The current value of the specified sequence.
     * @throws SequenceNotFoundException if the sequence is not found.
     */
    public long getCurrentValue(final String id) throws SequenceNotFoundException {
        nonNull(id);
        final Session session = sessionFactory.getCurrentSession();
        final Sequence sequence = (Sequence) session.get(Sequence.class, id, LockOptions.READ);
        if (sequence == null) {
            throw new SequenceNotFoundException(id);
        }
        return sequence.getCurrent();
    }

    /**
     * Gets the next value of a sequence. The row is locked in the current transaction.
     * @param id Sequence name.
     * @return The next value of the specified sequence.
     * @throws SequenceNotFoundException if the sequence is not found.
     */
    public long getNextValue(final String id) throws SequenceNotFoundException {
        nonNull(id);
        final Session session = sessionFactory.getCurrentSession();
        final Sequence sequence = (Sequence) session.get(Sequence.class, id, LockOptions.UPGRADE);
        if (sequence == null) {
            throw new SequenceNotFoundException(id);
        }
        final long next = sequence.getNext();
        session.update(sequence);
        return next;
    }

    /**
     * Gets the next value of a sequence, creating it if it does not exist.
     * @param id Sequence name.
     * @param initial Initial value.
     * @param increment Increment between values.
     * @return The next value of the specified sequence.
     */
    public long getNextValue(final String id, final long initial, final long increment) {
        nonNull(id);
        final Session session = sessionFactory.getCurrentSession();
        Sequence sequence = (Sequence) session.get(Sequence.class, id, LockOptions.UPGRADE);
        if (sequence != null) {
            return sequence.getNext();
        }
        // Create a new sequence and save it.
        sequence = new Sequence(id, initial, increment);
        session.save(sequence);
        // TODO: handle duplicates.
        return initial;
    }
}