QgsAggregateCalculator Class Reference

Utility class for calculating aggregates for a field (or expression) over the features from a vector layer. More...

#include <qgsaggregatecalculator.h>

Classes
struct	AggregateInfo
	Structured information about the available aggregates. More...
struct	AggregateParameters
	A bundle of parameters controlling aggregate calculation. More...

Public Member Functions
	QgsAggregateCalculator (const QgsVectorLayer *layer)
	Constructor for QgsAggregateCalculator.
QVariant	calculate (Qgis::Aggregate aggregate, const QString &fieldOrExpression, QgsExpressionContext *context=nullptr, bool *ok=nullptr, QgsFeedback *feedback=nullptr) const
	Calculates the value of an aggregate.
QString	delimiter () const
	Returns the delimiter used for joining values with the StringConcatenate aggregate.
QString	filter () const
	Returns the filter which limits the features used during the aggregate calculation.
QString	lastError () const
	Returns the last error encountered during the aggregate calculation.
const QgsVectorLayer *	layer () const
	Returns the associated vector layer.
void	setDelimiter (const QString &delimiter)
	Sets the delimiter to use for joining values with the StringConcatenate aggregate.
void	setFidsFilter (const QgsFeatureIds &fids)
	Sets a filter to limit the features used during the aggregate calculation.
void	setFilter (const QString &filterExpression)
	Sets a filter to limit the features used during the aggregate calculation.
void	setParameters (const AggregateParameters &parameters)
	Sets all aggregate parameters from a parameter bundle.

Static Public Member Functions
static QList< QgsAggregateCalculator::AggregateInfo >	aggregates ()
	Structured information for available aggregates.
static QString	displayName (Qgis::Aggregate aggregate)
	Returns the friendly display name for a aggregate.
static Qgis::Aggregate	stringToAggregate (const QString &string, bool *ok=nullptr)
	Converts a string to a aggregate type.

Detailed Description

Utility class for calculating aggregates for a field (or expression) over the features from a vector layer.

Note

It is recommended that QgsVectorLayer::aggregate() is used rather then directly using this class, as the QgsVectorLayer method can handle delegating aggregate calculation to a data provider for remote calculation.

Definition at line 42 of file qgsaggregatecalculator.h.

Constructor & Destructor Documentation

QgsAggregateCalculator()

QgsAggregateCalculator::QgsAggregateCalculator

(

const QgsVectorLayer *

layer

)

Constructor for QgsAggregateCalculator.

Parameters

layer

vector layer to calculate aggregate from

Definition at line 30 of file qgsaggregatecalculator.cpp.

Member Function Documentation

aggregates()

QList< QgsAggregateCalculator::AggregateInfo > QgsAggregateCalculator::aggregates ( )

static

Structured information for available aggregates.

Since

QGIS 3.2

Definition at line 312 of file qgsaggregatecalculator.cpp.

calculate()

QVariant QgsAggregateCalculator::calculate	(	Qgis::Aggregate	aggregate,
		const QString &	fieldOrExpression,
		QgsExpressionContext *	context = nullptr,
		bool *	ok = nullptr,
		QgsFeedback *	feedback = nullptr
	)		const

Calculates the value of an aggregate.

Parameters

aggregate	aggregate to calculate
fieldOrExpression	source field or expression to use as basis for aggregated values. If an expression is used, then the context parameter must be set.
context	expression context for evaluating expressions
ok	if specified, will be set to true if aggregate calculation was successful. If ok is false then lastError() can be used to retrieve a descriptive error message.
feedback	optional feedback argument for early cancellation (since QGIS 3.22). If set, this will take precedence over any feedback object set on the expression context.

Returns

calculated aggregate value

Definition at line 54 of file qgsaggregatecalculator.cpp.

delimiter()

QString QgsAggregateCalculator::delimiter ( ) const

inline

Returns the delimiter used for joining values with the StringConcatenate aggregate.

See also

setDelimiter()

Definition at line 142 of file qgsaggregatecalculator.h.

displayName()

QString QgsAggregateCalculator::displayName ( Qgis::Aggregate  aggregate )

static

Returns the friendly display name for a aggregate.

Since

QGIS 3.22

Definition at line 260 of file qgsaggregatecalculator.cpp.

filter()

QString QgsAggregateCalculator::filter ( ) const

inline

Returns the filter which limits the features used during the aggregate calculation.

See also

setFilter()

Definition at line 129 of file qgsaggregatecalculator.h.

lastError()

QString QgsAggregateCalculator::lastError ( ) const

inline

Returns the last error encountered during the aggregate calculation.

Since

QGIS 3.22

Definition at line 97 of file qgsaggregatecalculator.h.

layer()

const QgsVectorLayer * QgsAggregateCalculator::layer

(

)

const

Returns the associated vector layer.

Definition at line 36 of file qgsaggregatecalculator.cpp.

setDelimiter()

void QgsAggregateCalculator::setDelimiter ( const QString &  delimiter )

inline

Sets the delimiter to use for joining values with the StringConcatenate aggregate.

Parameters

delimiter

string delimiter

See also

delimiter()

Definition at line 136 of file qgsaggregatecalculator.h.

setFidsFilter()

void QgsAggregateCalculator::setFidsFilter

(

const QgsFeatureIds &

fids

)

Sets a filter to limit the features used during the aggregate calculation.

If an expression filter is set, it will override this filter.

Parameters

fids	feature ids for feature filtering, and empty list will return no features.

See also

filter()

Definition at line 48 of file qgsaggregatecalculator.cpp.

setFilter()

void QgsAggregateCalculator::setFilter ( const QString &  filterExpression )

inline

Sets a filter to limit the features used during the aggregate calculation.

Parameters

filterExpression

expression for filtering features, or empty string to remove filter

See also

filter()

Definition at line 115 of file qgsaggregatecalculator.h.

setParameters()

void QgsAggregateCalculator::setParameters

(

const AggregateParameters &

parameters

)

Sets all aggregate parameters from a parameter bundle.

Parameters

parameters

aggregate parameters

Definition at line 41 of file qgsaggregatecalculator.cpp.

stringToAggregate()

Qgis::Aggregate QgsAggregateCalculator::stringToAggregate ( const QString &  string, bool *  ok = nullptr  )

static

Converts a string to a aggregate type.

Parameters

string	string to convert
ok	if specified, will be set to true if conversion was successful

Returns

aggregate type

Definition at line 202 of file qgsaggregatecalculator.cpp.

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The documentation for this class was generated from the following files:

• /build/qgis-3.40.0+99sid/src/core/qgsaggregatecalculator.h
• /build/qgis-3.40.0+99sid/src/core/qgsaggregatecalculator.cpp