/*
* Copyright Aduna (http://www.aduna-software.com/) (c) 2007-2008.
* Copyright James Leigh (c) 2006.
*
* Licensed under the Aduna BSD-style license.
*/
package org.openrdf.query.algebra.evaluation.impl;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import org.openrdf.query.BindingSet;
import org.openrdf.query.algebra.And;
import org.openrdf.query.algebra.Filter;
import org.openrdf.query.algebra.LeftJoin;
import org.openrdf.query.algebra.QueryModel;
import org.openrdf.query.algebra.QueryModelNode;
import org.openrdf.query.algebra.TupleExpr;
import org.openrdf.query.algebra.ValueExpr;
import org.openrdf.query.algebra.Var;
import org.openrdf.query.algebra.evaluation.QueryOptimizer;
import org.openrdf.query.algebra.helpers.QueryModelVisitorBase;
/**
* Splits conjunctive constraints into separate constraints. Treats LeftJoin
* condition as a filter if only references variables from the right side.
*
* @author Arjohn Kampman
*/
public class ConjunctiveConstraintSplitter implements QueryOptimizer {
public void optimize(QueryModel query, BindingSet bindings) {
query.visit(new ConstraintVisitor(query));
}
protected class ConstraintVisitor extends QueryModelVisitorBase<RuntimeException> {
protected final TupleExpr tupleExpr;
public ConstraintVisitor(TupleExpr tupleExpr) {
this.tupleExpr = tupleExpr;
}
/**
* If any conjunctive constraints only reference the right side, split
* them out of the condition into the right side.
*/
@Override
public void meet(LeftJoin node) {
super.meet(node);
ValueExpr condition = node.getCondition();
if (condition != null) {
And and = new And();
List<ValueExpr> constraints = new ArrayList<ValueExpr>(16);
getConjunctiveConstraints(condition, constraints);
for (int i = constraints.size() - 1; i >= 0; i--) {
ValueExpr constraint = constraints.get(i);
TupleExpr right = node.getRightArg();
Set<String> filterVars = new VarFinder(constraint).getVars();
if (right.getBindingNames().containsAll(filterVars)) {
node.setRightArg(new Filter(right.clone(), constraint.clone()));
}
else {
and.addArg(constraint);
}
}
if (and.getNumberOfArguments() > 1) {
node.setCondition(and);
}
else if (and.getNumberOfArguments() == 1) {
node.setCondition(and.getArg(0));
}
else {
node.setCondition(null);
}
}
}
@Override
public void meet(Filter filter) {
super.meet(filter);
List<ValueExpr> conjunctiveConstraints = new ArrayList<ValueExpr>(16);
getConjunctiveConstraints(filter.getCondition(), conjunctiveConstraints);
TupleExpr filterArg = filter.getArg();
for (int i = conjunctiveConstraints.size() - 1; i >= 1; i--) {
Filter newFilter = new Filter(filterArg, conjunctiveConstraints.get(i));
filterArg = newFilter;
}
filter.setCondition(conjunctiveConstraints.get(0));
filter.setArg(filterArg);
}
protected void getConjunctiveConstraints(ValueExpr valueExpr, List<ValueExpr> conjunctiveConstraints) {
if (valueExpr instanceof And) {
And and = (And)valueExpr;
for (ValueExpr arg : and.getArgs()) {
getConjunctiveConstraints(arg, conjunctiveConstraints);
}
}
else {
conjunctiveConstraints.add(valueExpr);
}
}
class VarFinder extends QueryModelVisitorBase<RuntimeException> {
private QueryModelNode node;
private Set<String> vars;
public VarFinder(QueryModelNode node) {
this.node = node;
}
public Set<String> getVars() {
vars = new HashSet<String>();
node.visit(this);
return vars;
}
@Override
public void meet(Var var) {
vars.add(var.getName());
}
}
}
}