QgsFeatureRequest::OrderByClause class

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

Contents

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.

Constructors, destructors, conversion operators

OrderByClause(const QString& expression, bool ascending = true)
Creates a new OrderByClause for a QgsFeatureRequest.
OrderByClause(const QString& expression, bool ascending, bool nullsfirst)
Creates a new OrderByClause for a QgsFeatureRequest.
OrderByClause(const QgsExpression& expression, bool ascending = true)
Creates a new OrderByClause for a QgsFeatureRequest.
OrderByClause(const QgsExpression& expression, bool ascending, bool nullsfirst)
Creates a new OrderByClause for a QgsFeatureRequest.

Public functions

auto ascending() const -> bool
Order ascending.
auto dump() const -> QString
Dumps the content to an SQL equivalent.
auto expression() const -> QgsExpression
The expression.
auto nullsFirst() const -> bool
Set if NULLS should be returned first.
auto prepare(QgsExpressionContext* context) -> bool
Prepare the expression with the given context.
void setAscending(bool ascending)
Set if ascending order is requested.
void setNullsFirst(bool nullsFirst)
Set if NULLS should be returned first.

Function documentation

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

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

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

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

bool QgsFeatureRequest::OrderByClause::ascending() const

Order ascending.

Returns If ascending order is requested

QgsExpression QgsFeatureRequest::OrderByClause::expression() const

The expression.

Returns the expression

bool QgsFeatureRequest::OrderByClause::nullsFirst() const

Set if NULLS should be returned first.

Returns if NULLS should be returned first

bool QgsFeatureRequest::OrderByClause::prepare(QgsExpressionContext* context)

Prepare the expression with the given context.