Expression function for use within a QgsExpressionContextScope. More...

#include <qgsexpressioncontext.h>

Inheritance diagram for QgsScopedExpressionFunction:

Public Member Functions
	QgsScopedExpressionFunction (const QString &fnname, int params, const QString &group, const QString &helpText=QString(), bool usesGeometry=false, const QSet< QString > &referencedColumns=QSet< QString >(), bool lazyEval=false, bool handlesNull=false, bool isContextual=true)
	Create a new QgsScopedExpressionFunction. More...

	QgsScopedExpressionFunction (const QString &fnname, const QgsExpressionFunction::ParameterList &params, const QString &group, const QString &helpText=QString(), bool usesGeometry=false, const QSet< QString > &referencedColumns=QSet< QString >(), bool lazyEval=false, bool handlesNull=false, bool isContextual=true)
	Create a new QgsScopedExpressionFunction using named parameters. More...

virtual QgsScopedExpressionFunction *	clone () const =0
	Returns a clone of the function. More...

QVariant	func (const QVariantList &values, const QgsExpressionContext context, QgsExpression parent, const QgsExpressionNodeFunction *node) override=0
	Returns result of evaluating the function. More...

bool	isStatic (const QgsExpressionNodeFunction node, QgsExpression parent, const QgsExpressionContext *context) const override
	Will be called during prepare to determine if the function is static. More...

QSet< QString >	referencedColumns (const QgsExpressionNodeFunction *node) const override
	Returns a set of field names which are required for this function. More...

bool	usesGeometry (const QgsExpressionNodeFunction *node) const override
	Does this function use a geometry object. More...

Public Member Functions inherited from QgsExpressionFunction
	QgsExpressionFunction (const QString &fnname, int params, const QString &group, const QString &helpText=QString(), bool lazyEval=false, bool handlesNull=false, bool isContextual=false)
	Constructor for function which uses unnamed parameters. More...

	QgsExpressionFunction (const QString &fnname, int params, const QStringList &groups, const QString &helpText=QString(), bool lazyEval=false, bool handlesNull=false, bool isContextual=false)
	Constructor for function which uses unnamed parameters and group list. More...

	QgsExpressionFunction (const QString &fnname, const QgsExpressionFunction::ParameterList &params, const QString &group, const QString &helpText=QString(), bool lazyEval=false, bool handlesNull=false, bool isContextual=false)
	Constructor for function which uses named parameter list. More...

	QgsExpressionFunction (const QString &fnname, const QgsExpressionFunction::ParameterList &params, const QStringList &groups, const QString &helpText=QString(), bool lazyEval=false, bool handlesNull=false, bool isContextual=false)
	Constructor for function which uses named parameter list and group list. More...

virtual	~QgsExpressionFunction ()=default

virtual QStringList	aliases () const
	Returns a list of possible aliases for the function. More...

QString	group () const
	Returns the first group which the function belongs to. More...

QStringList	groups () const
	Returns a list of the groups the function belongs to. More...

virtual bool	handlesNull () const
	Returns `true` if the function handles NULL values in arguments by itself, and the default NULL value handling should be skipped. More...

const QString	helpText () const
	The help text for the function. More...

bool	isContextual () const
	Returns whether the function is only available if provided by a QgsExpressionContext object. More...

virtual bool	isDeprecated () const
	Returns `true` if the function is deprecated and should not be presented as a valid option to users in expression builders. More...

bool	lazyEval () const
	`true` if this function should use lazy evaluation. More...

int	minParams () const
	The minimum number of parameters this function takes. More...

QString	name () const
	The name of the function. More...

bool	operator== (const QgsExpressionFunction &other) const

const QgsExpressionFunction::ParameterList &	parameters () const
	Returns the list of named parameters for the function, if set. More...

int	params () const
	The number of parameters this function takes. More...

virtual bool	prepare (const QgsExpressionNodeFunction node, QgsExpression parent, const QgsExpressionContext *context) const
	This will be called during the prepare step() of an expression if it is not static. More...

virtual QVariant	run (QgsExpressionNode::NodeList args, const QgsExpressionContext context, QgsExpression parent, const QgsExpressionNodeFunction node)
	Evaluates the function, first evaluating all required arguments before passing them to the function's func() method. More...

Additional Inherited Members
Public Types inherited from QgsExpressionFunction
typedef QVariant(*	FcnEval) (const QVariantList &values, const QgsExpressionContext context, QgsExpression parent, const QgsExpressionNodeFunction *node)
	Function definition for evaluation against an expression context, using a list of values as parameters to the function. More...

typedef QList< QgsExpressionFunction::Parameter >	ParameterList
	List of parameters, used for function definition. More...

Static Protected Member Functions inherited from QgsExpressionFunction
static bool	allParamsStatic (const QgsExpressionNodeFunction node, QgsExpression parent, const QgsExpressionContext *context)
	This will return `true` if all the params for the provided function node are static within the constraints imposed by the context within the given parent. More...

Detailed Description

Expression function for use within a QgsExpressionContextScope.

This differs from a standard QgsExpression::Function in that it requires an implemented clone() method.

Since: QGIS 2.12

Definition at line 37 of file qgsexpressioncontext.h.

Constructor & Destructor Documentation

◆ QgsScopedExpressionFunction() [1/2]

QgsScopedExpressionFunction::QgsScopedExpressionFunction	(	const QString &	fnname,
		int	params,
		const QString &	group,
		const QString &	helpText = `QString()`,
		bool	usesGeometry = `false`,
		const QSet< QString > &	referencedColumns = `QSet<QString>()`,
		bool	lazyEval = `false`,
		bool	handlesNull = `false`,
		bool	isContextual = `true`
	)

inline

Create a new QgsScopedExpressionFunction.

Since: QGIS 2.12

Definition at line 46 of file qgsexpressioncontext.h.

◆ QgsScopedExpressionFunction() [2/2]

QgsScopedExpressionFunction::QgsScopedExpressionFunction	(	const QString &	fnname,
		const QgsExpressionFunction::ParameterList &	params,
		const QString &	group,
		const QString &	helpText = `QString()`,
		bool	usesGeometry = `false`,
		const QSet< QString > &	referencedColumns = `QSet<QString>()`,
		bool	lazyEval = `false`,
		bool	handlesNull = `false`,
		bool	isContextual = `true`
	)

inline

Create a new QgsScopedExpressionFunction using named parameters.

Since: QGIS 3.0

Definition at line 65 of file qgsexpressioncontext.h.

Member Function Documentation

◆ clone()

virtual QgsScopedExpressionFunction* QgsScopedExpressionFunction::clone ( ) const

pure virtual

Returns a clone of the function.

◆ func()

QVariant QgsScopedExpressionFunction::func	(	const QVariantList &	values,
		const QgsExpressionContext *	context,
		QgsExpression *	parent,
		const QgsExpressionNodeFunction *	node
	)

overridepure virtual

Returns result of evaluating the function.

Parameters

values	list of values passed to the function
context	context expression is being evaluated against
parent	parent expression
node	expression node

Returns: result of function

Implements QgsExpressionFunction.

◆ isStatic()

bool QgsScopedExpressionFunction::isStatic	(	const QgsExpressionNodeFunction *	node,
		QgsExpression *	parent,
		const QgsExpressionContext *	context
	)		const

overridevirtual

Will be called during prepare to determine if the function is static.

A function is static if it will return the same value for every feature with different attributes and/or geometry.

By default this will return true, if all arguments that have been passed to the function are also static.

Since: QGIS 3.0

Reimplemented from QgsExpressionFunction.

Definition at line 820 of file qgsexpressioncontextutils.cpp.

◆ referencedColumns()

QSet< QString > QgsScopedExpressionFunction::referencedColumns ( const QgsExpressionNodeFunction * node ) const

overridevirtual

Returns a set of field names which are required for this function.

May contain QgsFeatureRequest::AllAttributes to signal that all attributes are required. If in doubt this will return more fields than strictly required.