com.hazelcast.query.impl.getters

Class MultiResult<T>

java.lang.Object

com.hazelcast.query.impl.getters.MultiResult<T>

Type Parameters:

T - type of the underlying result store in the MultiResult

Direct Known Subclasses:

ImmutableMultiResult

public class MultiResult<T>
extends Object

Represents multiple results from a single attribute extraction.

MultiResult is an aggregate of results that is returned if the ValueExtractor returns multiple results due to a reduce operation executed on a hierarchy of values.

It sounds counter-intuitive, but a single extraction may return multiple values when arrays or collections are involved.

Let's have a look at the following data structure:

 class Swap {
     Leg legs[2];
 }
 class Leg {
     String currency;
 }
 

The following extraction of the currency attribute legs[any].currency results in two currencies for each Leg. In order to return both values in one result of the extract operation both currencies are returned in a single MultiResult object where each result contains a name of the currency. It allows the user to operate on multiple "reduced" values as if they were single-values.

Let's have a look at the following queries:

• leg[1].currency = 'EUR'
• leg[any].currency = 'EUR'

In the first query, the extraction will return just one currency, whereas the extraction in the second query will return a MultiResult containing two currencies. During the evaluation of the "=" equals predicate the MultiResult will be "unfolded" and the condition will evaluated against all currencies from the MultiResult. If there is "any" currency that matches the condition the whole predicate will be evaluated to "true" and the matching Swap will be returned. As a result all Swaps will be returned where there's at lease one Leg with EUR currency.

Other examples:

• legs -> returns one 'single-value' result -> a collection of values
• legs[0] -> returns one 'single result' - a Leg object
• legs[0].currency -> returns one 'multi value' result - an array of Legs
• legs[any] -> returns a MultiResult - that contains a collection of Leg objects
• legs[any].currency -> returns a MultiResult - that contains a collection of String objects

Constructor Summary

Constructors

Constructor and Description
MultiResult()
MultiResult(List<T> results)

Method Summary

Modifier and Type	Method and Description
void	add(T result)
void	addNullOrEmptyTarget()
List<T>	getResults()
boolean	isEmpty()
boolean	isNullEmptyTarget()
void	setNullOrEmptyTarget(boolean nullOrEmptyTarget)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

MultiResult

public MultiResult()

MultiResult

public MultiResult(List<T> results)

Method Detail

add

public void add(T result)

Parameters:

result - result to be added to this MultiResult

addNullOrEmptyTarget

public void addNullOrEmptyTarget()

getResults

public List<T> getResults()

Returns:

a mutable underlying list of collected results

isEmpty

public boolean isEmpty()

Returns:

true if the MultiResult is empty; false otherwise

isNullEmptyTarget

public boolean isNullEmptyTarget()

setNullOrEmptyTarget

public void setNullOrEmptyTarget(boolean nullOrEmptyTarget)