rowsource.java

這是一個油Java實作的資料庫系統 是個入門的好材料

/* =============================================================
 * SmallSQL : a free Java DBMS library for the Java(tm) platform
 * =============================================================
 *
 * (C) Copyright 2004-2007, by Volker Berlin.
 *
 * Project Info:  http://www.smallsql.de/
 *
 * This library is free software; you can redistribute it and/or modify it 
 * under the terms of the GNU Lesser General Public License as published by 
 * the Free Software Foundation; either version 2.1 of the License, or 
 * (at your option) any later version.
 *
 * This library 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 library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, 
 * USA.  
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc. 
 * in the United States and other countries.]
 *
 * ---------------
 * RowSource.java
 * ---------------
 * Author: Volker Berlin
 * 
 */
package smallsql.database;

import java.sql.*;
import smallsql.database.language.Language;

/**
 * This is the navigation through the rows of any source.
 * This is an abstract class and not an interface because interfaces are ever public.
 * All Implementations are used as a Source in the FROM clause.
 * 
 * Know Implementations are:
 * - Join
 * - TableResult
 * - ViewResult
 * - MemoryResult
 * - GroupResult (extends from MemoryResult)
 * - SortedResult
 * - UnionAll
 * 
 * Future Implementations are:
 * - Inner SELECT
 * - row function
 */
abstract class RowSource {
	
	
	/**
	 * If this RowSource is scrollable. It means it can scroll in all directions.
	 */
	abstract boolean isScrollable();
	
	/**
	 * Equals to ResultSet.beforeFirst()
	 */
	abstract void beforeFirst() throws Exception;

	
	
	/**
	 * Equals to ResultSet.isBeforeFirst().
	 */
	boolean isBeforeFirst() throws SQLException{
		throw SmallSQLException.create(Language.RSET_FWDONLY);
	}

	/**
	 * Equals to ResultSet.isFirst().
	 */
	boolean isFirst() throws SQLException{
		throw SmallSQLException.create(Language.RSET_FWDONLY);
	}
    

	/**
	 * Equals to ResultSet.first()
	 * @return
	 */
    abstract boolean first() throws Exception;

	boolean previous() throws Exception{
		throw SmallSQLException.create(Language.RSET_FWDONLY);
	}
	
    abstract boolean next() throws Exception;
    
    
	boolean last() throws Exception{
		throw SmallSQLException.create(Language.RSET_FWDONLY);
	}
	
	
	/**
	 * Equals to ResultSet.isLast().
	 */
	boolean isLast() throws Exception{
		throw SmallSQLException.create(Language.RSET_FWDONLY);
	}

	/**
	 * Equals to ResultSet.isAfterLast().
	 */
	boolean isAfterLast() throws SQLException, Exception{
		throw SmallSQLException.create(Language.RSET_FWDONLY);
	}
    

	abstract void afterLast() throws Exception;
	
	
	boolean absolute(int row) throws Exception{
		throw SmallSQLException.create(Language.RSET_FWDONLY);
	}
	
	
	boolean relative(int rows) throws Exception{
		throw SmallSQLException.create(Language.RSET_FWDONLY);
	}
	
	
	abstract int getRow() throws Exception;
	
    
    
    /**
     * Get a marker for the current row. The method setRowPostion must be reconstruct
     * the current row. The RowPosition can be a file offset for TableResult.
     * This is using for SortedResult.
     * @return The value need be >= 0.
     * It can be a counter for MemoryResult.
     */
	abstract long getRowPosition();

	/**
	 * Restore the row that was marked with the value. This is using for SortedResult.
	 * @param rowPosition Only values that are return from getRowPosition are valid.
	 */
	abstract void setRowPosition(long rowPosition) throws Exception;
	
	/**
	 * Is used for OUTER JOIN to set the RowSource to NULL if the row exists
	 * only in the major RowSource (table)
	 */
	abstract void nullRow();
	
	/**
	 * Is used for JOIN to set both site to "No current row". This is needed if
	 * one site has 0 rows that the getXXX() methods throw this exception.
	 */
	abstract void noRow();
	
	
	/**
	 * If the current row is inserted in this ResultSet.
	 */
	abstract boolean rowInserted();
	
	/**
	 * If the current row is deleted.
	 */
	abstract boolean rowDeleted();
	
	/**
	 * Returns true if a alias was set and no more alias can be set. 
	 * This is used from the SQLParser
	 * @return 
	 */
    boolean hasAlias(){
    	return true;
    }
	

    void setAlias(String name) throws SQLException{
        throw SmallSQLException.create(Language.ALIAS_UNSUPPORTED);
    }
    
    /**
     * Perform some operation on some RowSources per ResultSet. For example the grouping
     * on GroupResult and sorting on SortedResult.
     */
    abstract void execute() throws Exception;
    
    
    /**
     * Check if the list of ExpressionName based on this RowSource.
     * @param columns list of ExpressionNames
     * @return false if one or more ExpressionName that not based on this RowSource
     * @see Utils#getExpressionNameFromTree(Expression)
     */
    abstract boolean isExpressionsFromThisRowSource(Expressions columns);

}