An expression node which takes it value from a feature's field. More...

#include <qgsexpressionnodeimpl.h>

Inheritance diagram for QgsExpressionNodeColumnRef:

Public Member Functions
	QgsExpressionNodeColumnRef (const QString &name)
	Constructor for QgsExpressionNodeColumnRef, referencing the column with the specified name. More...

QgsExpressionNode *	clone () const override
	Generate a clone of this node. More...

QString	dump () const override
	Dump this node into a serialized (part) of an expression. More...

QVariant	evalNode (QgsExpression parent, const QgsExpressionContext context) override
	Abstract virtual eval method Errors are reported to the parent. More...

bool	isStatic (QgsExpression parent, const QgsExpressionContext context) const override
	Returns `true` if this node can be evaluated for a static value. More...

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

bool	needsGeometry () const override
	Abstract virtual method which returns if the geometry is required to evaluate this expression. More...

QList< const QgsExpressionNode * >	nodes () const override
	Returns a list of all nodes which are used in this expression. More...

QgsExpressionNode::NodeType	nodeType () const override
	Gets the type of this node. More...

bool	prepareNode (QgsExpression parent, const QgsExpressionContext context) override
	Abstract virtual preparation method Errors are reported to the parent. More...

QSet< QString >	referencedColumns () const override
	Abstract virtual method which returns a list of columns required to evaluate this node. More...

QSet< QString >	referencedFunctions () const override
	Returns a set of all functions which are used in this expression. More...

QSet< QString >	referencedVariables () const override
	Returns a set of all variables which are used in this expression. More...

Public Member Functions inherited from QgsExpressionNode
virtual	~QgsExpressionNode ()=default

QVariant	cachedStaticValue () const
	Returns the node's static cached value. More...

virtual QgsExpressionNode *	clone () const =0
	Generate a clone of this node. More...

virtual QString	dump () const =0
	Dump this node into a serialized (part) of an expression. More...

const QgsExpressionNode *	effectiveNode () const
	Returns a reference to the simplest node which represents this node, after any compilation optimizations have been applied. More...

QVariant	eval (QgsExpression parent, const QgsExpressionContext context)
	Evaluate this node with the given context and parent. More...

bool	hasCachedStaticValue () const
	Returns `true` if the node can be replaced by a static cached value. More...

virtual bool	isStatic (QgsExpression parent, const QgsExpressionContext context) const =0
	Returns `true` if this node can be evaluated for a static value. More...

virtual bool	needsGeometry () const =0
	Abstract virtual method which returns if the geometry is required to evaluate this expression. More...

virtual QList< const QgsExpressionNode * >	nodes () const =0
	Returns a list of all nodes which are used in this expression. More...

virtual QgsExpressionNode::NodeType	nodeType () const =0
	Gets the type of this node. More...

bool	prepare (QgsExpression parent, const QgsExpressionContext context)
	Prepare this node for evaluation. More...

virtual QSet< QString >	referencedColumns () const =0
	Abstract virtual method which returns a list of columns required to evaluate this node. More...

virtual QSet< QString >	referencedFunctions () const =0
	Returns a set of all functions which are used in this expression. More...

virtual QSet< QString >	referencedVariables () const =0
	Returns a set of all variables which are used in this expression. More...

void	setCachedStaticValue (const QVariant &value) const
	Sets the cached static value for the node. More...

Additional Inherited Members
Public Types inherited from QgsExpressionNode
enum	NodeType { ntUnaryOperator , ntBinaryOperator , ntInOperator , ntFunction , ntLiteral , ntColumnRef , ntCondition , ntIndexOperator , ntBetweenOperator }
	Known node types. More...

Public Attributes inherited from QgsExpressionNode
int	parserFirstColumn = 0
	First column in the parser this node was found. More...

int	parserFirstLine = 0
	First line in the parser this node was found. More...

int	parserLastColumn = 0
	Last column in the parser this node was found. More...

int	parserLastLine = 0
	Last line in the parser this node was found. More...

Protected Member Functions inherited from QgsExpressionNode
	QgsExpressionNode ()=default
	Constructor. More...

	QgsExpressionNode (const QgsExpressionNode &other)
	Copy constructor. More...

void	cloneTo (QgsExpressionNode *target) const
	Copies the members of this node to the node provided in target. More...

QgsExpressionNode &	operator= (const QgsExpressionNode &other)
	Assignment operator. More...

Protected Attributes inherited from QgsExpressionNode
QVariant	mCachedStaticValue
	Contains the static, precalculated value for the node if mHasCachedValue is `true`. More...

std::unique_ptr< QgsExpressionNode >	mCompiledSimplifiedNode
	Contains a compiled node which represents a simplified version of this node as a result of compilation optimizations. More...

bool	mHasCachedValue = false
	`true` if the node has a static, precalculated value. More...

Detailed Description

An expression node which takes it value from a feature's field.

Definition at line 512 of file qgsexpressionnodeimpl.h.

Constructor & Destructor Documentation

◆ QgsExpressionNodeColumnRef()

QgsExpressionNodeColumnRef::QgsExpressionNodeColumnRef ( const QString & name )

inline

Constructor for QgsExpressionNodeColumnRef, referencing the column with the specified name.

Definition at line 520 of file qgsexpressionnodeimpl.h.

Member Function Documentation

◆ clone()

QgsExpressionNode * QgsExpressionNodeColumnRef::clone ( ) const

overridevirtual

Generate a clone of this node.

Ownership is transferred to the caller.

Returns: a deep copy of this node.

Implements QgsExpressionNode.

Definition at line 1531 of file qgsexpressionnodeimpl.cpp.

◆ dump()

QString QgsExpressionNodeColumnRef::dump ( ) const

overridevirtual

Dump this node into a serialized (part) of an expression.

The returned expression does not necessarily literally match the original expression, it's just guaranteed to behave the same way.

Implements QgsExpressionNode.

Definition at line 1497 of file qgsexpressionnodeimpl.cpp.

◆ evalNode()

QVariant QgsExpressionNodeColumnRef::evalNode	(	QgsExpression *	parent,
		const QgsExpressionContext *	context
	)

overridevirtual

Abstract virtual eval method Errors are reported to the parent.

Since: QGIS 3.0

Implements QgsExpressionNode.

Definition at line 1435 of file qgsexpressionnodeimpl.cpp.

◆ isStatic()

bool QgsExpressionNodeColumnRef::isStatic	(	QgsExpression *	parent,
		const QgsExpressionContext *	context
	)		const

overridevirtual

Returns true if this node can be evaluated for a static value.

This is used during the prepare() step and in case it returns true, the value of this node will already be evaluated and the result cached (and therefore not re-evaluated in subsequent calls to eval()). In case this returns true, prepareNode() will never be called.

Since: QGIS 3.0

Implements QgsExpressionNode.

Definition at line 1538 of file qgsexpressionnodeimpl.cpp.

◆ name()

QString QgsExpressionNodeColumnRef::name ( ) const

inline

The name of the column.

Definition at line 534 of file qgsexpressionnodeimpl.h.

◆ needsGeometry()

bool QgsExpressionNodeColumnRef::needsGeometry ( ) const

overridevirtual

Abstract virtual method which returns if the geometry is required to evaluate this expression.

This needs to call needsGeometry() recursively on any child nodes.

Returns: true if a geometry is required to evaluate this expression

Implements QgsExpressionNode.

Definition at line 1526 of file qgsexpressionnodeimpl.cpp.

◆ nodes()

QList< const QgsExpressionNode * > QgsExpressionNodeColumnRef::nodes ( ) const

overridevirtual

Returns a list of all nodes which are used in this expression.

Note: not available in Python bindings

Since: QGIS 3.2

Implements QgsExpressionNode.

Definition at line 1519 of file qgsexpressionnodeimpl.cpp.

◆ nodeType()

QgsExpressionNode::NodeType QgsExpressionNodeColumnRef::nodeType ( ) const

overridevirtual

Gets the type of this node.

Returns: The type of this node

Implements QgsExpressionNode.

Definition at line 1470 of file qgsexpressionnodeimpl.cpp.

◆ prepareNode()

bool QgsExpressionNodeColumnRef::prepareNode	(	QgsExpression *	parent,
		const QgsExpressionContext *	context
	)

overridevirtual

Abstract virtual preparation method Errors are reported to the parent.

Since: QGIS 3.0

Implements QgsExpressionNode.

Definition at line 1475 of file qgsexpressionnodeimpl.cpp.

◆ referencedColumns()

QSet< QString > QgsExpressionNodeColumnRef::referencedColumns ( ) const

overridevirtual

Abstract virtual method which returns a list of columns required to evaluate this node.

When reimplementing this, you need to return any column that is required to evaluate this node and in addition recursively collect all the columns required to evaluate child nodes.

Warning: If the expression has been prepared via a call to QgsExpression::prepare(), or a call to QgsExpressionNode::prepare() for a node has been made, then some nodes in the expression may have been determined to evaluate to a static pre-calculatable value. In this case the results will omit attribute indices which are used by these pre-calculated nodes, regardless of their actual referenced columns. If you are seeking to use these functions to introspect an expression you must take care to do this with an unprepared expression node.