#include <coherence/util/aggregator/GroupAggregator.hpp>
Inherits Object, PortableObject, and InvocableMap::EntryAggregator.
Inherited by ParallelGroupAggregator.
The splitting (grouping) is performed using the results of the underlying ValueExtractor in such a way that two entries will belong to the same group if and only if the result of the corresponding ValueExtractor::extract extract call produces the same value or tuple (list of values). After the entries are split into the groups, the underlying aggregator is applied separately to each group. The result of the aggregation by the GroupAggregator is a Map that has distinct values (or tuples) as keys and results of the individual aggregation as values. Additionally, those results could be further reduced using an optional Filter object.
Informally speaking, this aggregator is analogous to the SQL "group by" and "having" clauses. Note that the "having" Filter is applied independently on each server against the partial aggregation results; this generally implies that data affinity is required to ensure that all required data used to generate a given result exists within a single cache partition. In other words, the "group by" predicate should not span multiple partitions if the "having" clause is used.
The GroupAggregator is somewhat similar to the DistinctValues aggregator, which returns back a list of distinct values (tuples) without performing any additional aggregation work.
Unlike many other concrete EntryAggregator implementations that are constructed directly, instances of GroupAggregator should only be created using one of the factory methods: create(ValueExtractor, InvocableMap::EntryAggregator) create(vExtractor, hAggregator), create(ValueExtractor, InvocableMap::EntryAggregator, Filter),
Public Types | ||||
| typedef spec::Handle | Handle | |||
| GroupAggregator Handle definition. | ||||
| typedef spec::View | View | |||
| GroupAggregator View definition. | ||||
| typedef spec::Holder | Holder | |||
| GroupAggregator Holder definition. | ||||
Public Member Functions | ||||
| virtual Object::Holder | aggregate (Set::View vSetEntries) | |||
| Process a set of InvocableMap::Entry objects in order to produce an aggregated result.
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| virtual void | readExternal (PofReader::Handle hIn) | |||
| virtual void | writeExternal (PofWriter::Handle hOut) const | |||
| virtual bool | equals (Object::View v) const | |||
| virtual size32_t | hashCode () const | |||
| Return a hash code value for the Object. This method is supported for the benefit of hash-based containers.
The general contract of
The default implementation is identity based.
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virtual TypedHandle < const String > | toString () const | |||
| Output a human-readable description of this Object to the given stream. Note that when overriding this method the return type must be TypedHandle<const String> rather then String::View. These two types are assignment compatible but not equivalent and declaring the override with String::View will not be a compatible override. coherence::lang::operator<<(std::ostream, Object::View) is defined and will call into the toString method, to output Objects. If a managed String object is desired, the COH_TO_STRING macro can be used to build up a String from streamable contents and is generally how toString() will be implemented.
Object::View vKey = ... Object::View vValue = ... std::cout << vKey << " = " << vValue << std::endl; String::View vs = COH_TO_STRING(vKey << " = " << vValue); The COH_TO_STRING macro is also the most common way to implement the toString method. For example:
virtual TypedHandle<const String> Person::toString() const { return COH_TO_STRING("Name: " << f_sName << " SSN: " << f_nSSN); }
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| virtual ValueExtractor::View | getExtractor () const | |||
| Obtain the underlying ValueExtractor. | ||||
| virtual InvocableMap::EntryAggregator::Handle | getAggregator () | |||
| Obtain the underlying EntryAggregator. | ||||
| virtual InvocableMap::EntryAggregator::View | getAggregator () const | |||
| Obtain the underlying EntryAggregator. | ||||
Static Public Member Functions | ||||
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static GroupAggregator::Handle | create () | |||
| Default constructor (necessary for the PortableObject interface). | ||||
| static GroupAggregator::Handle | create (ValueExtractor::View vExtractor, InvocableMap::EntryAggregator::Handle hAggregator, Filter::View vFilter=NULL) | |||
| Create an instance of GroupAggregator based on a specified extractor and an coherence::util::InvocableMap::EntryAggregator and a result evaluation filter. | ||||
Protected Attributes | ||||
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FinalView < ValueExtractor > | f_vExtractor | |||
| The underlying ValueExtractor. | ||||
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FinalHandle < InvocableMap::EntryAggregator > | f_hAggregator | |||
| The underlying EntryAggregator. | ||||
| FinalView< Filter > | f_vFilter | |||
| The underlying Filter. | ||||
| static GroupAggregator::Handle create | ( | ValueExtractor::View | vExtractor, | |
| InvocableMap::EntryAggregator::Handle | hAggregator, | |||
| Filter::View | vFilter = NULL | |||
| ) | [static] |
Create an instance of GroupAggregator based on a specified extractor and an coherence::util::InvocableMap::EntryAggregator and a result evaluation filter.
| vExtractor | a ValueExtractor that will be used to split a set of InvocableMap entries into distinct groups | |
| hAggregator | an underlying EntryAggregator | |
| vFilter | an optional Filter object used to filter out results of individual group aggregation results |
| virtual ValueExtractor::View getExtractor | ( | ) | const [virtual] |
| virtual InvocableMap::EntryAggregator::Handle getAggregator | ( | ) | [virtual] |
Obtain the underlying EntryAggregator.
| virtual InvocableMap::EntryAggregator::View getAggregator | ( | ) | const [virtual] |
Obtain the underlying EntryAggregator.