Application: gvSIG desktop

package com.hardcode.gdbms.engine;

import java.io.IOException;

import com.hardcode.gdbms.engine.data.DataSource;

import com.hardcode.gdbms.engine.data.DriverException;

import com.hardcode.gdbms.engine.instruction.Expression;

import com.hardcode.gdbms.engine.instruction.SelectAdapter;

import com.hardcode.gdbms.engine.instruction.SemanticException;

import com.hardcode.gdbms.engine.instruction.UnionAdapter;

import com.hardcode.gdbms.engine.instruction.Utilities;

/**

 * Strategy de pruebas, en la que los metodos tienen la caracter?stica de que

 * son los m?s f?ciles de implementar en el momento en que fueron necesarios

 *

 * @author Fernando Gonz?lez Cort?s

 */

public class FirstStrategy implements Strategy {

    /**

     * @see com.hardcode.gdbms.engine.Strategy#select(com.hardcode.gdbms.parser.ASTSQLSelectCols,

     *      com.hardcode.gdbms.parser.ASTSQLTableList,

     *      com.hardcode.gdbms.parser.ASTSQLWhere)

     */

    public DataSource select(SelectAdapter instr)

        throws DriverException, SemanticException, IOException {

        DataSource ret = null;

        DataSource[] fromTables = instr.getTables();

        DataSource prod = new PDataSource(fromTables);

        ret = prod;

        /*

         * Se establece como origen de datos el DataSource producto de las tablas

         * de la cl?usula from para que el acceso desde el objeto field a los

         * valores del dataSource sea correcto

         */

        Utilities.setTablesAndSource((SelectAdapter) instr, fromTables, prod);

        Expression[] fields = instr.getFieldsExpression();

        if (fields != null) {

            ret.start();

            DataSource res = new ProjectionDataSource(prod, fields,

                    instr.getFieldsAlias());

            ret.stop();

            ret = res;

        } else {

            ret = prod;

        }

        Expression whereExpression = instr.getWhereExpression();

        if (whereExpression != null) {

            ret.start();

            FilteredDataSource dataSource = new FilteredDataSource(ret,

                    whereExpression);

            dataSource.filtrar();

            ret.stop();

            ret = dataSource;

        }

        return ret;

    }

    /**

     * @see com.hardcode.gdbms.engine.Strategy#union(com.hardcode.gdbms.engine.instruction.UnionInstruction)

     */

    public DataSource union(UnionAdapter instr)

        throws DriverException, IOException, SemanticException {

        return new UnionDataSource(instr.getFirstTable(), instr.getSecondTable());

    }

}