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

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 *  to you 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,
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 *  See the License for the specific language governing permissions and
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package org.apache.polygene.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.
     */
    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.
     */
    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).
     */
    class NeedOnChange
        implements ReindexingStrategy
    {
        @Override
        public boolean reindexingNeeded( String dbAppVersion, String currentAppVersion )
        {
            return !dbAppVersion.equals( currentAppVersion );
        }
    }

}