QGIS API Documentation 3.39.0-Master (9ea1ddbe645)
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Expression function for use within a QgsExpressionContextScope. More...
#include <qgsexpressioncontext.h>
Public Member Functions | |
QgsScopedExpressionFunction (const QString &fnname, const QgsExpressionFunction::ParameterList ¶ms, 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. | |
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. | |
virtual QgsScopedExpressionFunction * | clone () const =0 |
Returns a clone of the function. | |
QVariant | func (const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent, const QgsExpressionNodeFunction *node) override=0 |
Returns result of evaluating the function. | |
bool | isStatic (const QgsExpressionNodeFunction *node, QgsExpression *parent, const QgsExpressionContext *context) const override |
Will be called during prepare to determine if the function is static. | |
QSet< QString > | referencedColumns (const QgsExpressionNodeFunction *node) const override |
Returns a set of field names which are required for this function. | |
bool | usesGeometry (const QgsExpressionNodeFunction *node) const override |
Does this function use a geometry object. | |
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QgsExpressionFunction (const QString &fnname, const QgsExpressionFunction::ParameterList ¶ms, const QString &group, const QString &helpText=QString(), bool lazyEval=false, bool handlesNull=false, bool isContextual=false) | |
Constructor for function which uses named parameter list. | |
QgsExpressionFunction (const QString &fnname, const QgsExpressionFunction::ParameterList ¶ms, 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. | |
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. | |
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. | |
virtual | ~QgsExpressionFunction ()=default |
virtual QStringList | aliases () const |
Returns a list of possible aliases for the function. | |
QString | group () const |
Returns the first group which the function belongs to. | |
QStringList | groups () const |
Returns a list of the groups the function belongs to. | |
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. | |
const QString | helpText () const |
The help text for the function. | |
bool | isContextual () const |
Returns whether the function is only available if provided by a QgsExpressionContext object. | |
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. | |
bool | lazyEval () const |
true if this function should use lazy evaluation. | |
int | minParams () const |
The minimum number of parameters this function takes. | |
QString | name () const |
The name of the function. | |
bool | operator== (const QgsExpressionFunction &other) const |
const QgsExpressionFunction::ParameterList & | parameters () const |
Returns the list of named parameters for the function, if set. | |
int | params () const |
The number of parameters this function takes. | |
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. | |
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. | |
Additional Inherited Members | |
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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. | |
typedef QList< QgsExpressionFunction::Parameter > | ParameterList |
List of parameters, used for function definition. | |
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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. | |
Expression function for use within a QgsExpressionContextScope.
This differs from a standard QgsExpression::Function in that it requires an implemented clone() method.
Definition at line 42 of file qgsexpressioncontext.h.
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inline |
Create a new QgsScopedExpressionFunction.
Definition at line 50 of file qgsexpressioncontext.h.
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inline |
Create a new QgsScopedExpressionFunction using named parameters.
Definition at line 68 of file qgsexpressioncontext.h.
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pure virtual |
Returns a clone of the function.
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overridepure virtual |
Returns result of evaluating the function.
values | list of values passed to the function |
context | context expression is being evaluated against |
parent | parent expression |
node | expression node |
Implements QgsExpressionFunction.
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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.
Reimplemented from QgsExpressionFunction.
Definition at line 969 of file qgsexpressioncontextutils.cpp.
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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.
Reimplemented from QgsExpressionFunction.
Definition at line 963 of file qgsexpressioncontextutils.cpp.
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overridevirtual |
Does this function use a geometry object.
Reimplemented from QgsExpressionFunction.
Definition at line 957 of file qgsexpressioncontextutils.cpp.