PointExprFactory.java

package org.openrdf.sail.rdbms.algebra.factories;

import static org.openrdf.sail.rdbms.algebra.base.SqlExprSupport.sqlNull;
import static org.openrdf.sail.rdbms.algebra.base.SqlExprSupport.str;
import static org.openrdf.sail.rdbms.algebra.base.SqlExprSupport.unsupported;

import org.openrdf.model.Literal;
import org.openrdf.model.Value;
import org.openrdf.query.algebra.Datatype;
import org.openrdf.query.algebra.Lang;
import org.openrdf.query.algebra.MathExpr;
import org.openrdf.query.algebra.QueryModelNode;
import org.openrdf.query.algebra.Str;
import org.openrdf.query.algebra.ValueConstant;
import org.openrdf.query.algebra.ValueExpr;
import org.openrdf.query.algebra.Var;
import org.openrdf.query.algebra.helpers.QueryModelVisitorBase;
import org.openrdf.sail.rdbms.algebra.PointColumn;
import org.openrdf.sail.rdbms.algebra.SqlNull;
import org.openrdf.sail.rdbms.algebra.base.SqlExpr;
import org.openrdf.sail.rdbms.exceptions.UnsupportedRdbmsOperatorException;

/**
 * Creates an SQL expression of a literal's point value.
 * 
 * @author Christian Becker
 */
public class PointExprFactory extends
		QueryModelVisitorBase<UnsupportedRdbmsOperatorException> {
	protected SqlExpr result;

	public SqlExpr createPointExpr(ValueExpr expr)
			throws UnsupportedRdbmsOperatorException {
		result = null;
		if (expr == null)
			return new SqlNull();
		expr.visit(this);
		if (result == null)
			return new SqlNull();
		return result;
	}

	@Override
	public void meet(Datatype node) {
		result = sqlNull();
	}

	@Override
	public void meet(Lang node) throws UnsupportedRdbmsOperatorException {
		result = sqlNull();
	}

	@Override
	public void meet(MathExpr node) throws UnsupportedRdbmsOperatorException {
		result = sqlNull();
	}

	@Override
	public void meet(Str node) {
		result = sqlNull();
	}

	@Override
	public void meet(ValueConstant vc) {
		result = valueOf(vc.getValue());
	}

	@Override
	public void meet(Var var) {
		if (var.getValue() == null) {
			result = new PointColumn(var);
		} else {
			result = valueOf(var.getValue());
		}
	}

	@Override
	protected void meetNode(QueryModelNode arg)
			throws UnsupportedRdbmsOperatorException {
		throw unsupported(arg);
	}

	private SqlExpr valueOf(Value value) {
		if (value instanceof Literal) {
			return str(((Literal) value).getLabel());
		}
		return sqlNull();
	}

}