Package org.eclipse.rdf4j.query.algebra

Class ProjectionElem

java.lang.Object

org.eclipse.rdf4j.query.algebra.AbstractQueryModelNode

org.eclipse.rdf4j.query.algebra.ProjectionElem

All Implemented Interfaces:

Serializable, Cloneable, QueryModelNode, VariableScopeChange

public class ProjectionElem
extends AbstractQueryModelNode

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 Extensions).

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 target name that maps each projection variable name to one of subject, predicate, object or context.

Author:

Jeen Broekstra

See Also:

• Serialized Form

Constructor Summary

Constructors

Constructor	Description
ProjectionElem()	Create a new empty ProjectionElem.
ProjectionElem(String name)	Create a new ProjectionElem with a variable name.
ProjectionElem(String name, String targetName)	Create a new ProjectionElem with a variable name and an additional mapped target name

Method Summary

Modifier and Type	Method	Description
ProjectionElem	clone()	Returns a (deep) clone of this query model node.
boolean	equals(Object other)	Returns true if this query model node and its children are recursively equal to o and its children.
String	getName()	Get the name of the projection element (typically the name of the variable in the select expressions)
Optional<String>	getProjectionAlias()	Get the alias the projection element value should be mapped to.
String	getSignature()	Default implementation of QueryModelNode.getSignature() that prints the name of the node's class.
ExtensionElem	getSourceExpression()
boolean	hasAggregateOperatorInExpression()
int	hashCode()
void	replaceChildNode(QueryModelNode current, QueryModelNode replacement)	Replaces one of the child nodes with a new node.
void	setAggregateOperatorInExpression(boolean aggregateOperatorInExpression)
void	setName(String name)	Set the name of the projection element (typically the name of the variable in the select expressions)
void	setProjectionAlias(String alias)	Set the alias the projection element value should be mapped to.
void	setSourceExpression(ExtensionElem sourceExpression)
<X extends Exception> void	visit(QueryModelVisitor<X> visitor)	Visits this node.
<X extends Exception> void	visitChildren(QueryModelVisitor<X> visitor)	Visits the children of this node.

Methods inherited from class org.eclipse.rdf4j.query.algebra.AbstractQueryModelNode

getCardinality, getCostEstimate, getParentNode, getResultSizeActual, getResultSizeEstimate, getTotalTimeNanosActual, isCardinalitySet, isVariableScopeChange, nullEquals, replaceNodeInList, replaceWith, resetCardinality, setCardinality, setCostEstimate, setParentNode, setResultSizeActual, setResultSizeEstimate, setTotalTimeNanosActual, setVariableScopeChange, shouldCacheCardinality, toString

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Details

ProjectionElem

public ProjectionElem()

Create a new empty ProjectionElem.

ProjectionElem

public ProjectionElem(String name)

Create a new ProjectionElem with a variable name.

Parameters:

name - The name of the projection element (typically the name of the variable in the select expressions). May not be null.

ProjectionElem

public ProjectionElem(String name,
 String targetName)

Create a new ProjectionElem with a variable name and an additional mapped target name

Parameters:

name - The name of the projection element (typically the name of the variable in the select expressions). May not be null.

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.

Method Details

getName

public String getName()

Get the name of the projection element (typically the name of the variable in the select expressions)

setName

public void setName(String name)

Set the name of the projection element (typically the name of the variable in the select expressions)

Parameters:

name - the projection variable name. May not be null.

getProjectionAlias

public Optional<String> getProjectionAlias()

Get the alias the projection element value should be mapped to. Used in CONSTRUCT queries for mapping select expressions to statement patterns.

Returns:

an optionally empty projection alias.

setProjectionAlias

public void setProjectionAlias(String alias)

Set the alias the projection element value should be mapped to. Used in CONSTRUCT queries for mapping select expressions to statement patterns.

Parameters:

alias - the projection alias.

visit

public <X extends Exception> void visit(QueryModelVisitor<X> visitor)
                                 throws X

Description copied from interface: QueryModelNode

Visits this node. The node reports itself to the visitor with the proper runtime type.

Throws:

X

visitChildren

public <X extends Exception> void visitChildren(QueryModelVisitor<X> visitor)
                                         throws X

Description copied from interface: QueryModelNode

Visits the children of this node. The node calls QueryModelNode.visit(QueryModelVisitor) on all of its child nodes.

Throws:

X

replaceChildNode

public void replaceChildNode(QueryModelNode current,
 QueryModelNode replacement)

Description copied from interface: QueryModelNode

Replaces one of the child nodes with a new node.

Parameters:

current - The current child node.

replacement - The new child node.

getSignature

public String getSignature()

Description copied from class: AbstractQueryModelNode

Default implementation of QueryModelNode.getSignature() that prints the name of the node's class.

Specified by:

getSignature in interface QueryModelNode

Overrides:

getSignature in class AbstractQueryModelNode

Returns:

The node's signature, e.g. SLICE (offset=10, limit=10).

equals

public boolean equals(Object other)

Description copied from interface: QueryModelNode

Returns true if this query model node and its children are recursively equal to o and its children.

Specified by:

equals in interface QueryModelNode

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

clone

public ProjectionElem clone()

Description copied from interface: QueryModelNode

Returns a (deep) clone of this query model node. This method recursively clones the entire node tree, starting from this nodes.

Specified by:

clone in interface QueryModelNode

Overrides:

clone in class AbstractQueryModelNode

Returns:

A deep clone of this query model node.

hasAggregateOperatorInExpression

public boolean hasAggregateOperatorInExpression()

Returns:

Returns the aggregateOperatorInExpression.

setAggregateOperatorInExpression

public void setAggregateOperatorInExpression(boolean aggregateOperatorInExpression)

Parameters:

aggregateOperatorInExpression - The aggregateOperatorInExpression to set.

getSourceExpression

public ExtensionElem getSourceExpression()

Returns:

Returns the sourceExpression.

setSourceExpression

public void setSourceExpression(ExtensionElem sourceExpression)

Parameters:

sourceExpression - The sourceExpression to set.