org.eobjects.metamodel.jdbc.SplitQueriesDataSet Maven / Gradle / Ivy

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/**
 * eobjects.org MetaModel
 * Copyright (C) 2010 eobjects.org
 *
 * This copyrighted material is made available to anyone wishing to use, modify,
 * copy, or redistribute it subject to the terms and conditions of the GNU
 * Lesser General Public License, as published by the Free Software Foundation.
 *
 * 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 Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution; if not, write to:
 * Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor
 * Boston, MA  02110-1301  USA
 */

package org.eobjects.metamodel.jdbc;

import java.util.Iterator;
import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.eobjects.metamodel.DataContext;
import org.eobjects.metamodel.MetaModelException;
import org.eobjects.metamodel.data.AbstractDataSet;
import org.eobjects.metamodel.data.DataSet;
import org.eobjects.metamodel.data.Row;
import org.eobjects.metamodel.query.Query;
import org.eobjects.metamodel.query.SelectItem;

/**
 * DataSet for split queries. Queries will be executed as needed, not
 * at once.
 * 
 * @see org.eobjects.metamodel.jdbc.QuerySplitter
 */
final class SplitQueriesDataSet extends AbstractDataSet {

	private static final Logger logger = LoggerFactory
			.getLogger(SplitQueriesDataSet.class);
	private final DataContext _dataContext;
	private final SelectItem[] _selectItems;
	private Iterator _queryIterator;
	private DataSet _currentDataSet;
	private int _queryIndex = 0;

	public SplitQueriesDataSet(DataContext dataContext, List splitQueries) {
		if (dataContext == null || splitQueries == null) {
			throw new IllegalArgumentException("Arguments cannot be null");
		}
		_dataContext = dataContext;
		_queryIterator = splitQueries.iterator();
		if (splitQueries.size() == 0) {
			_selectItems = new SelectItem[0];
		} else {
			_selectItems = splitQueries.get(0).getSelectClause().getItems()
					.toArray(new SelectItem[0]);
		}
	}

	@Override
	public void close() {
		if (_currentDataSet != null) {
			logger.debug("currentDataSet.close()");
			_currentDataSet.close();
		}
		_currentDataSet = null;
		_queryIterator = null;
	}

	@Override
	public Row getRow() throws MetaModelException {
		if (_currentDataSet != null) {
			return _currentDataSet.getRow();
		}
		throw new IllegalStateException(
				"No rows available. Either DataSet is closed or next() hasn't been called");
	}

	@Override
	public SelectItem[] getSelectItems() {
		return _selectItems;
	}

	@Override
	public boolean next() {
		boolean result;
		if (_currentDataSet == null) {
			result = false;
		} else {
			result = _currentDataSet.next();
		}
		if (!result && _queryIterator.hasNext()) {
			if (_currentDataSet != null) {
				logger.debug("currentDataSet.close()");
				_currentDataSet.close();
			}
			Query q = _queryIterator.next();
			_currentDataSet = _dataContext.executeQuery(q);
			if (logger.isDebugEnabled()) {
				_queryIndex++;
				logger.debug("Executing query #{}", _queryIndex);
			}
			result = next();
		}
		return result;
	}
}