teichmann@6847: /* Copyright (C) 2011, 2012, 2013 by Bundesanstalt für Gewässerkunde
teichmann@6847:  * Software engineering by Intevation GmbH
teichmann@6847:  *
teichmann@6847:  * This file is Free Software under the GNU AGPL (>=v3)
teichmann@6847:  * and comes with ABSOLUTELY NO WARRANTY! Check out the
teichmann@6847:  * documentation coming with Dive4Elements River for details.
teichmann@6847:  */
teichmann@6847: 
teichmann@6847: package org.dive4elements.river.utils;
teichmann@6847: 
teichmann@6847: import java.util.ArrayList;
teichmann@6847: import java.util.HashMap;
teichmann@6847: import java.util.Iterator;
teichmann@6847: import java.util.List;
teichmann@6847: import java.util.Map;
teichmann@6847: 
teichmann@6847: import org.apache.log4j.Logger;
teichmann@6847: import org.hibernate.SQLQuery;
teichmann@6847: import org.hibernate.Session;
teichmann@6847: 
teichmann@6847: /** To reduce the number of SQL queries send to the backend
teichmann@6847:  *  (mainly by the fixings overviews) we execute them in batches of ids
teichmann@6847:  *  and store the results in a small cache.
teichmann@6847:  *  TODO: It currently relies on dynamic SQL.
teichmann@6847:  *  Is there a way to use Hibernate with java.sql.Array
teichmann@6847:  *  in cross database compatible manner?
teichmann@6847:  */
teichmann@6847: public abstract class BatchLoader<T> {
teichmann@6847: 
teichmann@6847:     private static Logger log = Logger.getLogger(BatchLoader.class);
teichmann@6847: 
teichmann@6847:     public static final int BATCH_SIZE = 100;
teichmann@6847: 
teichmann@6847:     private Map<Integer, T> loaded;
teichmann@6847:     private List<Integer>   rest;
teichmann@6847:     private Session         session;
teichmann@6847:     private String          sqlTemplate;
teichmann@6847: 
teichmann@6847:     public BatchLoader(
teichmann@6847:         List<Integer> columns,
teichmann@6847:         Session       session,
teichmann@6847:         String        sqlTemplate
teichmann@6847:     ) {
teichmann@6847:         rest             = new ArrayList<Integer>(columns.size());
teichmann@6847:         loaded           = new HashMap<Integer, T>();
teichmann@6847:         this.session     = session;
teichmann@6847:         this.sqlTemplate = sqlTemplate;
teichmann@6847: 
teichmann@6847:         // Insert in reverse order to minize searching.
teichmann@6847:         for (int i = columns.size()-1; i >= 0; --i) {
teichmann@6847:             rest.add(columns.get(i));
teichmann@6847:         }
teichmann@6847:     }
teichmann@6847: 
teichmann@6847:     /** Searches for id and fill a batch to load containing the found id. */
teichmann@6847:     private List<Integer> prepareBatch(int id) {
teichmann@6847:         List<Integer> batch = new ArrayList<Integer>(BATCH_SIZE);
teichmann@6847: 
teichmann@6847:         boolean found = false;
teichmann@6847: 
teichmann@6847:         for (int i = rest.size()-1; batch.size() < BATCH_SIZE && i >= 0; --i) {
teichmann@6847:             Integer cid = rest.get(i);
teichmann@6847:             if (cid == id) {
teichmann@6847:                 found = true;
teichmann@6847:                 batch.add(cid);
teichmann@6847:                 rest.remove(i);
teichmann@6847:             }
teichmann@6847:             else if ((found && batch.size() < BATCH_SIZE)
teichmann@6847:                  || (!found && batch.size() < BATCH_SIZE-1)) {
teichmann@6847:                 batch.add(cid);
teichmann@6847:                 rest.remove(i);
teichmann@6847:             }
teichmann@6847:         }
teichmann@6847: 
teichmann@6847:         return batch;
teichmann@6847:     }
teichmann@6847: 
teichmann@6847:     /** Converts id to a list of comma separated ints. */
teichmann@6847:     private static String idsAsString(List<Integer> ids) {
teichmann@6847:         StringBuilder sb = new StringBuilder();
teichmann@6847:         for (Iterator<Integer> i = ids.iterator(); i.hasNext();) {
teichmann@6847:             sb.append(i.next());
teichmann@6847:             if (i.hasNext()) {
teichmann@6847:                 sb.append(',');
teichmann@6847:             }
teichmann@6847:         }
teichmann@6847:         return sb.toString();
teichmann@6847:     }
teichmann@6847: 
teichmann@6847:     /** Get data for id. */
teichmann@6847:     public T get(int id) {
teichmann@6847:         T already = loaded.get(id);
teichmann@6847:         if (already != null) {
teichmann@6847:             return already;
teichmann@6847:         }
teichmann@6847: 
teichmann@6847:         List<Integer> batch = prepareBatch(id);
teichmann@6847:         if (batch.isEmpty()) {
teichmann@6847:             return null;
teichmann@6847:         }
teichmann@6847:         String sql = sqlTemplate.replace("$IDS", idsAsString(batch));
teichmann@6847:         if (log.isDebugEnabled()) {
teichmann@6847:             log.debug(sql + " " + sql.length());
teichmann@6847:         }
teichmann@6847:         fill(session.createSQLQuery(sql));
teichmann@6847:         return get(id);
teichmann@6847:     }
teichmann@6847: 
teichmann@6847:     /** Call this from fill() to store data in the cache. */
teichmann@6847:     protected void cache(int key, T data) {
teichmann@6847:         loaded.put(key, data);
teichmann@6847:     }
teichmann@6847: 
teichmann@6847:     /** Override this to fill the cache */
teichmann@6847:     protected abstract void fill(SQLQuery query);
teichmann@6847: }