de.topicmapslab.jexc.eXql.grammar.expression.SelectExpression.java Source code

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/*******************************************************************************
 * Copyright 2010, Topic Map Lab ( http://www.topicmapslab.de )
 * 
 * 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 de.topicmapslab.jexc.eXql.grammar.expression;

import java.util.Collection;
import java.util.LinkedList;
import java.util.List;

import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Workbook;

import de.topicmapslab.jexc.eXql.grammar.tokens.Comma;
import de.topicmapslab.jexc.eXql.grammar.tokens.Distinct;
import de.topicmapslab.jexc.eXql.grammar.tokens.ExqlToken;
import de.topicmapslab.jexc.eXql.grammar.tokens.Select;
import de.topicmapslab.jexc.eXql.parser.ExqlParser;
import de.topicmapslab.jexc.eXql.parser.IeXqlParserCallback;
import de.topicmapslab.jexc.eXql.result.ExqlResultSet;
import de.topicmapslab.jexc.eXql.result.ExqlResultSetImpl;
import de.topicmapslab.jexc.exception.JeXcException;

/**
 * @author Sven Krosse
 * 
 */
public class SelectExpression extends ExqlExpression {

    /**
     * internal flag indicates the distinct selection of entries
     */
    private final boolean distinct;

    /**
     * constructor
     * 
     * @param tokens
     *            the tokens
     */
    @SuppressWarnings("unchecked")
    public SelectExpression(List<ExqlToken> tokens) throws JeXcException {
        super(tokens);

        IeXqlParserCallback callback = new IeXqlParserCallback() {
            public void newToken(List<ExqlToken> tokens, ExqlToken foundDelimer) throws JeXcException {
                addExpression(new ValueExpression(tokens));
            }
        };

        ExqlParser.parseWithBracketDetection(callback, tokens, true, Select.class, Comma.class, Distinct.class);
        distinct = Distinct.class.equals(tokens.get(1).getClass());
    }

    /**
     * {@inheritDoc}
     */
    @SuppressWarnings("unchecked")
    public ExqlResultSet<?> interpret(Workbook workBook, Object... input) throws JeXcException {
        if (input.length != 1 && input[0] instanceof Collection<?>) {
            throw new JeXcException("Number of arguments is invalid, expect one collection!");
        }
        Collection<Row> rows = (Collection<Row>) input[0];
        List<List<Object>> results = new LinkedList<List<Object>>();
        List<Integer> rowIndexes = new LinkedList<Integer>();
        for (Row row : rows) {
            if (row == null) {
                continue;
            }
            List<Object> object = new LinkedList<Object>();
            boolean valid = true;
            for (ExqlExpression ex : getExpressions()) {
                Object result = ex.interpret(workBook, row);
                /*
                 * avoid null values
                 */
                if (result == null) {
                    valid = false;
                    break;
                }
                object.add(result);
            }
            if (valid) {
                /*
                 * filter duplicates if DISTINCT is used
                 */
                if (distinct && results.contains(object)) {
                    continue;
                }
                results.add(object);
                rowIndexes.add(row.getRowNum());
            }
        }
        return new ExqlResultSetImpl(rowIndexes, results);
    }
}