uniqueconstraint.java

开源的axion的数据库代码

/*
 * $Id: UniqueConstraint.java,v 1.11 2003/05/13 19:33:47 rwald Exp $
 * =======================================================================
 * Copyright (c) 2002-2003 Axion Development Team.  All rights reserved.
 *  
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions 
 * are met:
 * 
 * 1. Redistributions of source code must retain the above 
 *    copyright notice, this list of conditions and the following 
 *    disclaimer. 
 *   
 * 2. Redistributions in binary form must reproduce the above copyright 
 *    notice, this list of conditions and the following disclaimer in 
 *    the documentation and/or other materials provided with the 
 *    distribution. 
 *   
 * 3. The names "Tigris", "Axion", nor the names of its contributors may 
 *    not be used to endorse or promote products derived from this 
 *    software without specific prior written permission. 
 *  
 * 4. Products derived from this software may not be called "Axion", nor 
 *    may "Tigris" or "Axion" appear in their names without specific prior
 *    written permission.
 *   
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 
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 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 
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 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 * =======================================================================
 */

package org.axiondb.constraints;

import java.util.ArrayList;
import java.util.List;

import org.axiondb.AxionException;
import org.axiondb.Row;
import org.axiondb.RowDecorator;
import org.axiondb.RowIterator;
import org.axiondb.event.RowEvent;

/**
 * A UNIQUE constraint, which is violated
 * when my collection of {@link Selectable}s is 
 * not unique within my table.
 * 
 * @version $Revision: 1.11 $ $Date: 2003/05/13 19:33:47 $
 * @author Rodney Waldhoff
 * @author James Strachan
 */
public class UniqueConstraint extends BaseSelectableBasedConstraint {
    
    public UniqueConstraint(String name) {
        this(name,"UNIQUE");
    }
    
    public UniqueConstraint(String name, String type) {
        super(name,type);
    }
    
    public boolean evaluate(RowEvent event) throws AxionException {        
        if(null == event.getNewRow()) {
            return true;
        } else {
            RowDecorator dec = event.getTable().makeRowDecorator();
            dec.setRow(event.getNewRow());
            List values = new ArrayList(getSelectableCount());
            for(int i=0;i<getSelectableCount();i++) {
                values.add(getSelectable(i).evaluate(dec));
            }
            int acceptableRowId = -1;
            if(null != event.getOldRow()) {
                acceptableRowId = event.getOldRow().getIdentifier();
            }
            RowIterator matching = event.getTable().getMatchingRows(getSelectableList(),values);
            while(matching.hasNext()) {
                Row row = matching.next();
                if(-1 == acceptableRowId) {
                    // in this case, any matching row causes failure
                    return false; 
                } else if(row.getIdentifier() != acceptableRowId) {
                    // otherwise, check that the matching row isn't the one we're updating
                    return false;
                }
            }
            return true;
        }
    }

}