/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hp.hpl.jena.sparql.algebra.op;
import com.hp.hpl.jena.sparql.algebra.Op ;
import com.hp.hpl.jena.sparql.algebra.OpVisitor ;
import com.hp.hpl.jena.sparql.algebra.Table ;
import com.hp.hpl.jena.sparql.algebra.Transform ;
import com.hp.hpl.jena.sparql.algebra.table.TableUnit ;
import com.hp.hpl.jena.sparql.sse.Tags ;
import com.hp.hpl.jena.sparql.util.NodeIsomorphismMap ;
public class OpJoin extends Op2
{
/** Create join - an argument of null is
* simply dropped so Join.create(null, op) is op and Join.create(op,null) is op.
*/
public static Op create(Op left, Op right)
{
if ( left == null )
return right ;
if ( right == null )
return left ;
return new OpJoin(left, right) ;
}
/** Create join, removing any joins with the identity table and any nulls.
* <br>Join.create(null, op) is op.
* <br>Join.create(op, null) is op.
* <br>Join.create(TableUnit, op) is op.
* <br>Join.create(op, TableUnit) is op.
*/
public static Op createReduce(Op left, Op right)
{
if ( left == null || isJoinIdentify(left) )
return right ;
if ( right == null || isJoinIdentify(right) )
return left ;
return new OpJoin(left, right) ;
}
public static boolean isJoinIdentify(Op op)
{
if ( ! ( op instanceof OpTable ) )
return false ;
Table t = ((OpTable)op).getTable() ;
// Safe answer.
return TableUnit.isTableUnit(t) ;
}
private OpJoin(Op left, Op right) { super(left, right) ; }
@Override
public String getName() { return Tags.tagJoin ; }
@Override
public Op apply(Transform transform, Op left, Op right)
{ return transform.transform(this, left, right) ; }
@Override
public void visit(OpVisitor opVisitor) { opVisitor.visit(this) ; }
@Override
public Op2 copy(Op newLeft, Op newRight)
{ return new OpJoin(newLeft, newRight) ; }
@Override
public boolean equalTo(Op op2, NodeIsomorphismMap labelMap)
{
if ( ! ( op2 instanceof OpJoin) ) return false ;
return super.sameArgumentsAs((Op2)op2, labelMap) ;
}
}