| gvSIG desktop 1

package com.hardcode.gdbms.engine.strategies;

import com.hardcode.gdbms.engine.customQuery.CustomQuery;

import com.hardcode.gdbms.engine.customQuery.QueryException;

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

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

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

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

import com.hardcode.gdbms.engine.values.NumericValue;

import com.hardcode.gdbms.engine.values.Value;

	public OperationDataSource evaluate(DataSource[] tables, Expression[] values) throws QueryException {

		if (tables.length != 1) throw new QueryException("SUM only operates on one table");

		if (values.length != 1) throw new QueryException("SUM only operates with one value");

		((Adapter) values[0]).getInstructionContext().setFromTables(new DataSource[]{tables[0]});

		((Adapter) values[0]).getInstructionContext().setDs(tables[0]);

		String fieldName = values[0].getFieldName();

		if (fieldName == null) throw new QueryException("field not found " + Utilities.getText(((Adapter)values[0]).getEntity()));

		double res = 0;

		try {

			tables[0].start();

			int fieldIndex = tables[0].getFieldIndexByName(fieldName);

			if (fieldIndex == -1) throw new RuntimeException("we found the field name of the expression but could not find the field index?");

			for (int i = 0; i < tables[0].getRowCount(); i++) {

				Value v = tables[0].getFieldValue(i, fieldIndex);

				if (v instanceof NumericValue){

					throw new QueryException("SUM only operates with numeric fields");

				}

			}

			tables[0].stop();

			throw new QueryException("Error reading data", e);

		}

		return new SumDataSource(res);

	}