org.eclipse.rdf4j.query.algebra.ProjectionElem Maven / Gradle / Ivy
Show all versions of rdf4j-queryalgebra-model Show documentation
/*******************************************************************************
* Copyright (c) 2015 Eclipse RDF4J contributors, Aduna, and others.
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Distribution License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*******************************************************************************/
package org.eclipse.rdf4j.query.algebra;
import java.util.Objects;
import java.util.Optional;
/**
* Projection elements control which of the selected expressions (produced by the WHERE clause of a query) are returned
* in the solution, and the order in which they appear.
*
* In SPARQL SELECT queries, projection elements are the variables determined by the algorithm for finding SELECT
* expressions (see SPARQL 1.1 Query Language
* Recommendation, section 18.2.4.4). Each projection element will be a single variable name (any aliasing is
* handled by the use of {@link Extension}s).
*
* In SPARQL CONSTRUCT queries, the projection elements are used to map the variables obtained from the SELECT
* expressions to the required statement patterns. In this case, each projection element will have an additional
* {@link #getProjectionAlias() target name} that maps each projection variable name to one of {@code subject},
* {@code predicate}, {@code object} or {@code context}.
*
* @author Jeen Broekstra
*/
public class ProjectionElem extends AbstractQueryModelNode {
private static final long serialVersionUID = -8129811335486478066L;
private String name;
private String projectionAlias;
private boolean aggregateOperatorInExpression;
private ExtensionElem sourceExpression;
/**
* Create a new empty {@link ProjectionElem}.
*/
public ProjectionElem() {
}
/**
* Create a new {@link ProjectionElem} with a variable name.
*
* @param name The name of the projection element (typically the name of the variable in the select expressions).
* May not be null.
*/
public ProjectionElem(String name) {
this(name, null);
}
/**
* Create a new {@link ProjectionElem} with a variable name and an additional mapped {@link #getProjectionAlias()
* target name}
*
* @param name The name of the projection element (typically the name of the variable in the select
* expressions). May not be null.
* @param targetName The name of the variable the projection element value should be mapped to, to produce the
* projection. Used in CONSTRUCT queries for mapping select expressions to statement patterns. May
* be null.
*/
public ProjectionElem(String name, String targetName) {
setName(name);
setProjectionAlias(targetName);
}
/**
* Get the name of the projection element (typically the name of the variable in the select expressions)
*/
public String getName() {
return name;
}
/**
* Set the name of the projection element (typically the name of the variable in the select expressions)
*
* @param name the projection variable name. May not be {@code null}.
*/
public void setName(String name) {
this.name = Objects.requireNonNull(name);
}
/**
* Get the alias the projection element value should be mapped to. Used in CONSTRUCT queries for mapping select
* expressions to statement patterns.
*
* @return an optionally empty projection alias.
*/
public Optional getProjectionAlias() {
return Optional.ofNullable(projectionAlias);
}
/**
* Set the alias the projection element value should be mapped to. Used in CONSTRUCT queries for mapping select
* expressions to statement patterns.
*
* @param alias the projection alias.
*/
public void setProjectionAlias(String alias) {
this.projectionAlias = alias;
}
@Override
public void visit(QueryModelVisitor visitor) throws X {
visitor.meet(this);
}
@Override
public void visitChildren(QueryModelVisitor visitor) throws X {
// no-op
}
@Override
public void replaceChildNode(QueryModelNode current, QueryModelNode replacement) {
throw new IllegalArgumentException("Node is not a child node: " + current);
}
@Override
public String getSignature() {
StringBuilder sb = new StringBuilder(32);
sb.append(super.getSignature());
sb.append(" \"");
sb.append(name);
sb.append("\"");
if (projectionAlias != null) {
sb.append(" AS \"").append(projectionAlias).append("\"");
}
return sb.toString();
}
@Override
public boolean equals(Object other) {
if (other instanceof ProjectionElem) {
ProjectionElem o = (ProjectionElem) other;
return name.equals(o.getName()) && Objects.equals(getProjectionAlias(), o.getProjectionAlias());
}
return false;
}
@Override
public int hashCode() {
return Objects.hash(name, projectionAlias);
}
@Override
public ProjectionElem clone() {
return (ProjectionElem) super.clone();
}
/**
* @return Returns the aggregateOperatorInExpression.
*/
public boolean hasAggregateOperatorInExpression() {
return aggregateOperatorInExpression;
}
/**
* @param aggregateOperatorInExpression The aggregateOperatorInExpression to set.
*/
public void setAggregateOperatorInExpression(boolean aggregateOperatorInExpression) {
this.aggregateOperatorInExpression = aggregateOperatorInExpression;
}
/**
* @return Returns the sourceExpression.
*/
public ExtensionElem getSourceExpression() {
return sourceExpression;
}
/**
* @param sourceExpression The sourceExpression to set.
*/
public void setSourceExpression(ExtensionElem sourceExpression) {
this.sourceExpression = sourceExpression;
}
}