QgsFeatureRequest::OrderByClause Class Reference

The OrderByClause class represents an order by clause for a QgsFeatureRequest. More...

#include <qgsfeaturerequest.h>

Public Member Functions
	OrderByClause (const QString &expression, bool ascending=true)
	Creates a new OrderByClause for a QgsFeatureRequest. More...
	OrderByClause (const QString &expression, bool ascending, bool nullsfirst)
	Creates a new OrderByClause for a QgsFeatureRequest. More...
	OrderByClause (const QgsExpression &expression, bool ascending=true)
	Creates a new OrderByClause for a QgsFeatureRequest. More...
	OrderByClause (const QgsExpression &expression, bool ascending, bool nullsfirst)
	Creates a new OrderByClause for a QgsFeatureRequest. More...
bool	ascending () const
	Order ascending. More...
QString	dump () const
	Dumps the content to an SQL equivalent. More...
QgsExpression	expression () const
	The expression. More...
bool	nullsFirst () const
	Set if NULLS should be returned first. More...
bool	prepare (QgsExpressionContext *context)
	Prepare the expression with the given context. More...
void	setAscending (bool ascending)
	Set if ascending order is requested. More...
void	setNullsFirst (bool nullsFirst)
	Set if NULLS should be returned first. More...

Detailed Description

The OrderByClause class represents an order by clause for a QgsFeatureRequest.

It can be a simple field or an expression. Multiple order by clauses can be added to a QgsFeatureRequest to fine tune the behavior if a single field or expression is not enough to completely specify the required behavior.

If expression compilation is activated in the settings and the expression can be translated for the provider in question, it will be evaluated on provider side. If one of these two premises does not apply, the ordering will take place locally which results in increased memory and CPU usage.

If the ordering is done on strings, the order depends on the system's locale if the local fallback implementation is used. The order depends on the server system's locale and implementation if ordering is done on the server.

In case the fallback code needs to be used, a limit set on the request will be respected for the features returned by the iterator but internally all features will be requested from the provider.

Since

QGIS 2.14

Definition at line 126 of file qgsfeaturerequest.h.

Constructor & Destructor Documentation

OrderByClause() [1/4]

QgsFeatureRequest::OrderByClause::OrderByClause	(	const QString &	expression,
		bool	ascending = true
	)

Creates a new OrderByClause for a QgsFeatureRequest.

Parameters

expression	The expression to use for ordering
ascending	If the order should be ascending (1,2,3) or descending (3,2,1) If the order is ascending, by default nulls are last If the order is descending, by default nulls are first

Definition at line 356 of file qgsfeaturerequest.cpp.

OrderByClause() [2/4]

QgsFeatureRequest::OrderByClause::OrderByClause	(	const QString &	expression,
		bool	ascending,
		bool	nullsfirst
	)

Creates a new OrderByClause for a QgsFeatureRequest.

Parameters

expression	The expression to use for ordering
ascending	If the order should be ascending (1,2,3) or descending (3,2,1)
nullsfirst	If true, NULLS are at the beginning, if false, NULLS are at the end

Definition at line 364 of file qgsfeaturerequest.cpp.

OrderByClause() [3/4]

QgsFeatureRequest::OrderByClause::OrderByClause	(	const QgsExpression &	expression,
		bool	ascending = true
	)

Creates a new OrderByClause for a QgsFeatureRequest.

Parameters

expression	The expression to use for ordering
ascending	If the order should be ascending (1,2,3) or descending (3,2,1) If the order is ascending, by default nulls are last If the order is descending, by default nulls are first

Definition at line 371 of file qgsfeaturerequest.cpp.

OrderByClause() [4/4]

QgsFeatureRequest::OrderByClause::OrderByClause	(	const QgsExpression &	expression,
		bool	ascending,
		bool	nullsfirst
	)

Creates a new OrderByClause for a QgsFeatureRequest.

Parameters

expression	The expression to use for ordering
ascending	If the order should be ascending (1,2,3) or descending (3,2,1)
nullsfirst	If true, NULLS are at the beginning, if false, NULLS are at the end

Definition at line 379 of file qgsfeaturerequest.cpp.

Member Function Documentation

ascending()

bool QgsFeatureRequest::OrderByClause::ascending

(

)

const

Order ascending.

Returns

If ascending order is requested

Definition at line 387 of file qgsfeaturerequest.cpp.

dump()

QString QgsFeatureRequest::OrderByClause::dump

(

)

const

Dumps the content to an SQL equivalent.

Definition at line 407 of file qgsfeaturerequest.cpp.

expression()

QgsExpression QgsFeatureRequest::OrderByClause::expression

(

)

const

The expression.

Returns

the expression

Definition at line 415 of file qgsfeaturerequest.cpp.

nullsFirst()

bool QgsFeatureRequest::OrderByClause::nullsFirst

(

)

const

Set if NULLS should be returned first.

Returns

if NULLS should be returned first

Definition at line 397 of file qgsfeaturerequest.cpp.

prepare()

bool QgsFeatureRequest::OrderByClause::prepare

(

QgsExpressionContext *

context

)

Prepare the expression with the given context.

See also

QgsExpression::prepare

Since

QGIS 3.0

Definition at line 420 of file qgsfeaturerequest.cpp.

setAscending()

void QgsFeatureRequest::OrderByClause::setAscending

(

bool

ascending

)

Set if ascending order is requested.

Definition at line 392 of file qgsfeaturerequest.cpp.

setNullsFirst()

void QgsFeatureRequest::OrderByClause::setNullsFirst

(

bool

nullsFirst

)

Set if NULLS should be returned first.

Definition at line 402 of file qgsfeaturerequest.cpp.

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

• /tmp/buildd/qgis-3.6.0+99unstable/src/core/qgsfeaturerequest.h
• /tmp/buildd/qgis-3.6.0+99unstable/src/core/qgsfeaturerequest.cpp