Package org.elasticsearch.xpack.esql.core.expression

Class EmptyAttribute

java.lang.Object

org.elasticsearch.xpack.esql.core.tree.Node<Expression>

org.elasticsearch.xpack.esql.core.expression.Expression

org.elasticsearch.xpack.esql.core.expression.NamedExpression

org.elasticsearch.xpack.esql.core.expression.Attribute

org.elasticsearch.xpack.esql.core.expression.EmptyAttribute

All Implemented Interfaces:

NamedWriteable, Writeable, Resolvable

public class EmptyAttribute
extends Attribute

Marker for optional attributes. Acting as a dummy placeholder to avoid using null in the tree (which is not allowed). All empty attributes are considered equal.

Nested Class Summary

Nested classes/interfaces inherited from class org.elasticsearch.xpack.esql.core.expression.Attribute

Attribute.IdIgnoringWrapper

Nested classes/interfaces inherited from class org.elasticsearch.xpack.esql.core.expression.Expression

Expression.TypeResolution

Nested classes/interfaces inherited from interface org.elasticsearch.common.io.stream.Writeable

Writeable.Reader<V>, Writeable.Writer<V>

Field Summary

Fields inherited from class org.elasticsearch.xpack.esql.core.expression.Attribute

SYNTHETIC_ATTRIBUTE_NAME_PREFIX

Fields inherited from class org.elasticsearch.xpack.esql.core.tree.Node

TO_STRING_MAX_WIDTH

Constructor Summary

Constructors

Constructor	Description
EmptyAttribute(Source source)

Method Summary

Modifier and Type	Method	Description
protected Attribute	clone(Source source, String qualifier, String name, DataType type, Nullability nullability, NameId id, boolean synthetic)
DataType	dataType()	The DataType returned by executing the tree rooted at this expression.
String	getWriteableName()
protected NodeInfo<? extends Expression>	info()	Normally, you want to use one of the static create methods to implement this.
protected boolean	innerEquals(Object o, boolean ignoreIds)	The actual equality check, after shortcutting this == o and class checks.
protected int	innerHashCode(boolean ignoreIds)
boolean	isDimension()
boolean	isMetric()
protected String	label()
boolean	resolved()
boolean	semanticEquals(Expression other)	Whether this expression means the same as other, even if they are not exactly equal.
int	semanticHash()	A hash code that is consistent with Expression.semanticEquals(org.elasticsearch.xpack.esql.core.expression.Expression).
void	writeTo(StreamOutput out)

Methods inherited from class org.elasticsearch.xpack.esql.core.expression.Attribute

canonicalize, checkAndSerializeQualifier, dataTypeEquals, ignoreId, nodeString, nullable, qualifiedName, qualifier, rawTemporaryName, readQualifier, references, replaceChildren, toAttribute, toString, withDataType, withId, withLocation, withName, withNullability, withQualifier

Methods inherited from class org.elasticsearch.xpack.esql.core.expression.NamedExpression

equals, equals, hashCode, hashCode, id, name, synthetic

Methods inherited from class org.elasticsearch.xpack.esql.core.expression.Expression

canonical, childrenResolved, fold, foldable, propertiesToString, resolveType, typeResolved

Methods inherited from class org.elasticsearch.xpack.esql.core.tree.Node

anyMatch, children, collect, collectFirstChildren, collectLeaves, doCollectFirst, forEachDown, forEachDown, forEachDownMayReturnEarly, forEachProperty, forEachPropertyDown, forEachPropertyOnly, forEachPropertyUp, forEachUp, forEachUp, nodeName, nodeProperties, replaceChildrenSameSize, source, sourceLocation, sourceText, transformChildren, transformDown, transformDown, transformDown, transformNodeProps, transformPropertiesDown, transformPropertiesOnly, transformPropertiesUp, transformUp, transformUp, transformUp

Methods inherited from class java.lang.Object

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

Constructor Details

EmptyAttribute

public EmptyAttribute(Source source)

Method Details

writeTo

public void writeTo(StreamOutput out)
             throws IOException

Throws:

IOException

getWriteableName

public String getWriteableName()

clone

protected Attribute clone(Source source,
 String qualifier,
 String name,
 DataType type,
 Nullability nullability,
 NameId id,
 boolean synthetic)

Specified by:

clone in class Attribute

label

protected String label()

Specified by:

label in class Attribute

isDimension

public boolean isDimension()

Specified by:

isDimension in class Attribute

Returns:

true if the attribute represents a TSDB dimension type

isMetric

public boolean isMetric()

Specified by:

isMetric in class Attribute

Returns:

true if the attribute represents a TSDB metric type

resolved

public boolean resolved()

Specified by:

resolved in interface Resolvable

Overrides:

resolved in class Expression

dataType

public DataType dataType()

Description copied from class: Expression

The DataType returned by executing the tree rooted at this expression. If Expression.typeResolved() returns an error then the behavior of this method is undefined. It may return a valid type. Or it may throw an exception. Or it may return a totally nonsensical type.

Specified by:

dataType in class Expression

info

protected NodeInfo<? extends Expression> info()

Description copied from class: Node

Normally, you want to use one of the static create methods to implement this.

For QueryPlans, it is very important that the properties contain all of the expressions and references relevant to this node, and that all the properties are used in the provided constructor; otherwise query plan transformations like QueryPlan#transformExpressionsOnly(Function) will not have an effect.

Specified by:

info in class Node<Expression>

innerHashCode

protected int innerHashCode(boolean ignoreIds)

Overrides:

innerHashCode in class Attribute

innerEquals

protected boolean innerEquals(Object o,
 boolean ignoreIds)

Description copied from class: NamedExpression

The actual equality check, after shortcutting this == o and class checks.

Overrides:

innerEquals in class Attribute

semanticHash

public int semanticHash()

Description copied from class: Expression

A hash code that is consistent with Expression.semanticEquals(org.elasticsearch.xpack.esql.core.expression.Expression).

Overrides:

semanticHash in class Attribute

semanticEquals

public boolean semanticEquals(Expression other)

Description copied from class: Expression

Whether this expression means the same as other, even if they are not exactly equal. For example, a + b and b + a are not equal, but they are semantically equal.

If two expressions are equal, they are also semantically equal, but the reverse is generally not true.

Caution! Attribute.semanticEquals(Expression) is especially lenient, as it considers two attributes with the same NameId to be semantically equal, even if they have different data types or are represented using different classes.

But this doesn't extend to expressions containing attributes as children, which is pretty inconsistent. We have to revisit this before using Expression.semanticEquals(org.elasticsearch.xpack.esql.core.expression.Expression) in more places.

Overrides:

semanticEquals in class Attribute