extensions/indexing-sql/src/main/java/org/qi4j/index/sql/support/common/ReindexingStrategy.java

/*
 * Copyright (c) 2010, Stanislav Muhametsin. All Rights Reserved.
 *
 * 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 org.qi4j.index.sql.support.common;

/**
 * Service to decide when complete re-indexing is needed, along with default implementations. TODO
 * maybe add {@code void beganReindexing()} and {@code void finishedReindexing()} methods? For
 * example, for UI interaction.
 *
 * You can decide your application's re-indexing policy for example like this:
 * {@code mainModule.addServices(ReindexingStrategy.class).withMixins(ReindexingStrategy.AlwaysNeed.class);}
 * . This way your application will always re-index all entity store data at startup.
 */
public interface ReindexingStrategy
{
    boolean reindexingNeeded( String dbAppVersion, String currentAppVersion );

    /**
     * The re-indexing strategy which ALWAYS re-indexes everything. Useful with tests and during
     * early development stage of application.
     */
    public class AlwaysNeed
        implements ReindexingStrategy
    {
        @Override
        public boolean reindexingNeeded( String dbAppVersion, String currentAppVersion )
        {
            return true;
        }
    }

    /**
     * The re-indexing strategy which NEVER re-indexes anything. Useful when deleting and re-reading
     * data is something to be avoided at all costs.
     */
    public class NeverNeed
        implements ReindexingStrategy
    {
        @Override
        public boolean reindexingNeeded( String dbAppVersion, String currentAppVersion )
        {
            return false;
        }
    }

    /**
     * The re-indexing strategy, which re-indexes everything when application version changes.
     * Useful when migration from versions is implemented, or when application structure changes
     * along with version (but not during same version).
     */
    public class NeedOnChange
        implements ReindexingStrategy
    {
        @Override
        public boolean reindexingNeeded( String dbAppVersion, String currentAppVersion )
        {
            return !dbAppVersion.equals( currentAppVersion );
        }
    }

}