Class for parsing and evaluation of expressions (formerly called "search strings"). More...

#include <qgsexpression.h>

Classes
class	Function
	A abstract base class for defining QgsExpression functions. More...
class	Interval
class	Node
class	NodeBinaryOperator
class	NodeColumnRef
class	NodeCondition
class	NodeFunction
class	NodeInOperator
class	NodeList
class	NodeLiteral
class	NodeUnaryOperator
class	StaticFunction
class	Visitor
	support for visitor pattern - algorithms dealing with the expressions may be implemented without modifying the Node classes More...
class	WhenThen

Public Types
enum	UnaryOperator { uoNot, uoMinus }
enum	BinaryOperator { boOr, boAnd, boEQ, boNE, boLE, boGE, boLT, boGT, boRegexp, boLike, boNotLike, boILike, boNotILike, boIs, boIsNot, boPlus, boMinus, boMul, boDiv, boMod, boPow, boConcat }
enum	SpatialOperator { soBbox, soIntersects, soContains, soCrosses, soEquals, soDisjoint, soOverlaps, soTouches, soWithin }
enum	NodeType { ntUnaryOperator, ntBinaryOperator, ntInOperator, ntFunction, ntLiteral, ntColumnRef, ntCondition }
typedef QVariant(*	FcnEval )(const QVariantList &values, const QgsFeature f, QgsExpression parent)
typedef QList< WhenThen * >	WhenThenList

Public Member Functions
	QgsExpression (const QString &expr)
	~QgsExpression ()
bool	hasParserError () const
	Returns true if an error occurred when parsing the input expression.
QString	parserErrorString () const
	Returns parser error.
const Node *	rootNode () const
	Returns root node of the expression. Root node is null is parsing has failed.
bool	prepare (const QgsFields &fields)
	Get the expression ready for evaluation - find out column indexes.
QStringList	referencedColumns ()
	Get list of columns referenced by the expression.
bool	needsGeometry ()
	Returns true if the expression uses feature geometry for some computation.
QVariant	evaluate (const QgsFeature *f=NULL)
	Evaluate the feature and return the result.
QVariant	evaluate (const QgsFeature &f)
	Evaluate the feature and return the result.
QVariant	evaluate (const QgsFeature *f, const QgsFields &fields)
	Evaluate the feature and return the result.
QVariant	evaluate (const QgsFeature &f, const QgsFields &fields)
	Evaluate the feature and return the result.
bool	hasEvalError () const
	Returns true if an error occurred when evaluating last input.
QString	evalErrorString () const
	Returns evaluation error.
void	setEvalErrorString (QString str)
	Set evaluation error (used internally by evaluation functions)
void	setCurrentRowNumber (int rowNumber)
	Set the number for $rownum special column.
int	currentRowNumber ()
	Return the number used for $rownum special column.
void	setScale (double scale)
double	scale ()
const QString	expression () const
	Alias for dump()
QString	dump () const
	Return the expression string that represents this QgsExpression.
QgsDistanceArea *	geomCalculator ()
	Return calculator used for distance and area calculations (used by internal functions)
void	setGeomCalculator (const QgsDistanceArea &calc)
	Sets the geometry calculator used in evaluation of expressions,.
void	acceptVisitor (Visitor &v) const
	entry function for the visitor pattern

Static Public Member Functions
static void	setSpecialColumn (const QString &name, QVariant value)
	Assign a special column.
static void	unsetSpecialColumn (const QString &name)
	Unset a special column.
static QVariant	specialColumn (const QString &name)
	Return the value of the given special column or a null QVariant if undefined.
static bool	hasSpecialColumn (const QString &name)
	Check whether a special column exists.
static bool	isValid (const QString &text, const QgsFields &fields, QString &errorMessage)
static QString	replaceExpressionText (const QString &action, const QgsFeature feat, QgsVectorLayer layer, const QMap< QString, QVariant > substitutionMap=0, const QgsDistanceArea distanceArea=0)
	This function currently replaces each expression between [% and %] in the string with the result of its evaluation on the feature passed as argument.
static const QList< Function * > &	Functions ()
static const QStringList &	BuiltinFunctions ()
static bool	registerFunction (Function *function)
static bool	unregisterFunction (QString name)
static bool	isFunctionName (QString name)
static int	functionIndex (QString name)
static int	functionCount ()
	Returns the number of functions defined in the parser.
static QList< Function * >	specialColumns ()
	Returns a list of special Column definitions.
static QString	quotedColumnRef (QString name)
	return quoted column reference (in double quotes)
static QString	quotedString (QString text)
	return quoted string (in single quotes)
static QString	helptext (QString name)
static QString	group (QString group)

Static Public Attributes
static const char *	BinaryOperatorText []
static const char *	UnaryOperatorText []
static QList< Function * >	gmFunctions
static QStringList	gmBuiltinFunctions

Protected Member Functions
	QgsExpression ()
void	initGeomCalculator ()

Static Protected Member Functions
static void	initFunctionHelp ()

Protected Attributes
Node *	mRootNode
QString	mParserErrorString
QString	mEvalErrorString
int	mRowNumber
double	mScale
QString	mExp
QgsDistanceArea *	mCalc

Static Protected Attributes
static QMap< QString, QVariant >	gmSpecialColumns
static QMap< QString, QString >	gmSpecialColumnGroups
static QHash< QString, QString >	gFunctionHelpTexts
static QHash< QString, QString >	gGroups

Friends
class	QgsOgcUtils

Detailed Description

Class for parsing and evaluation of expressions (formerly called "search strings").

The expressions try to follow both syntax and semantics of SQL expressions.

Usage:

QgsExpression exp("gid*2 > 10 and type not in ('D','F'));
if (exp.hasParserError())
{
  // show error message with parserErrorString() and exit
}
QVariant result = exp.evaluate(feature, fields);
if (exp.hasEvalError())
{
  // show error message with evalErrorString()
}
else
{
  // examine the result
}

Possible QVariant value types:

invalid (null)
int
double
string
geometry

Similarly to SQL, this class supports three-value logic: true/false/unknown. Unknown value may be a result of operations with missing data (NULL). Please note that NULL is different value than zero or an empty string. For example 3 > NULL returns unknown.

There is no special (three-value) 'boolean' type: true/false is represented as 1/0 integer, unknown value is represented the same way as NULL values: invalid QVariant.

For better performance with many evaluations you may first call prepare(fields) function to find out indices of columns and then repeatedly call evaluate(feature).

Type conversion: operators and functions that expect arguments to be of particular type automatically convert the arguments to that type, e.g. sin('2.1') will convert the argument to a double, length(123) will first convert the number to a string. Explicit conversion can be achieved with toint, toreal, tostring functions. If implicit or explicit conversion is invalid, the evaluation returns an error. Comparison operators do numeric comparison in case both operators are numeric (int/double) or they can be converted to numeric types.

Arithmetic operators do integer arithmetics if both operands are integer. That is 2+2 yields integer 4, but 2.0+2 returns real number 4.0. There are also two versions of division and modulo operators: 1.0/2 returns 0.5 while 1/2 returns 0.

Member Typedef Documentation

typedef QVariant( * QgsExpression::FcnEval)(const QVariantList &values, const QgsFeature *f, QgsExpression *parent)

typedef QList<WhenThen*> QgsExpression::WhenThenList

Member Enumeration Documentation

enum QgsExpression::BinaryOperator

Enumerator:

boOr
boAnd
boEQ
boNE
boLE
boGE
boLT
boGT
boRegexp
boLike
boNotLike
boILike
boNotILike
boIs
boIsNot
boPlus
boMinus
boMul
boDiv
boMod
boPow
boConcat

enum QgsExpression::NodeType

Enumerator:

ntUnaryOperator
ntBinaryOperator
ntInOperator
ntFunction
ntLiteral
ntColumnRef
ntCondition

enum QgsExpression::SpatialOperator

Enumerator:

soBbox
soIntersects
soContains
soCrosses
soEquals
soDisjoint
soOverlaps
soTouches
soWithin

enum QgsExpression::UnaryOperator

Enumerator:

uoNot
uoMinus

Constructor & Destructor Documentation

QgsExpression::QgsExpression ( const QString & expr )

QgsExpression::~QgsExpression ( )

QgsExpression::QgsExpression ( )

inlineprotected

Member Function Documentation

void QgsExpression::acceptVisitor ( QgsExpression::Visitor & v ) const

entry function for the visitor pattern

const QStringList & QgsExpression::BuiltinFunctions ( )

static

int QgsExpression::currentRowNumber ( )

inline

Return the number used for $rownum special column.

QString QgsExpression::dump ( ) const

Return the expression string that represents this QgsExpression.

QString QgsExpression::evalErrorString ( ) const

inline

Returns evaluation error.

QVariant QgsExpression::evaluate ( const QgsFeature * f = NULL )

Evaluate the feature and return the result.

Note: prepare() should be called before calling this method

QVariant QgsExpression::evaluate ( const QgsFeature & f )

inline

Evaluate the feature and return the result.

Note: prepare() should be called before calling this method; available in python bindings as evaluatePrepared

QVariant QgsExpression::evaluate	(	const QgsFeature *	f,
		const QgsFields &	fields
	)

Evaluate the feature and return the result.

Note: this method does not expect that prepare() has been called on this instance

QVariant QgsExpression::evaluate	(	const QgsFeature &	f,
		const QgsFields &	fields
	)

inline

Evaluate the feature and return the result.

Note: this method does not expect that prepare() has been called on this instance; not available in python bindings

const QString QgsExpression::expression ( ) const

inline

Alias for dump()

int QgsExpression::functionCount ( )

static

Returns the number of functions defined in the parser.

Returns: The number of function defined in the parser.

int QgsExpression::functionIndex ( QString name )

static

const QList< QgsExpression::Function * > & QgsExpression::Functions ( )

static

QgsDistanceArea* QgsExpression::geomCalculator ( )

inline

Return calculator used for distance and area calculations (used by internal functions)

QString QgsExpression::group ( QString group )

static

bool QgsExpression::hasEvalError ( ) const

inline

Returns true if an error occurred when evaluating last input.

bool QgsExpression::hasParserError ( ) const

inline

Returns true if an error occurred when parsing the input expression.

bool QgsExpression::hasSpecialColumn ( const QString & name )

static

Check whether a special column exists.

Note: added in 2.2

QString QgsExpression::helptext ( QString name )

static

void QgsExpression::initFunctionHelp ( )

staticprotected

void QgsExpression::initGeomCalculator ( )

protected

bool QgsExpression::isFunctionName ( QString name )

static

bool QgsExpression::isValid	(	const QString &	text,
		const QgsFields &	fields,
		QString &	errorMessage
	)

static

bool QgsExpression::needsGeometry ( )

Returns true if the expression uses feature geometry for some computation.

QString QgsExpression::parserErrorString ( ) const

inline

Returns parser error.

bool QgsExpression::prepare ( const QgsFields & fields )

Get the expression ready for evaluation - find out column indexes.

QString QgsExpression::quotedColumnRef ( QString name )

static

return quoted column reference (in double quotes)

QString QgsExpression::quotedString ( QString text )

static

return quoted string (in single quotes)

QStringList QgsExpression::referencedColumns ( )

Get list of columns referenced by the expression.

Note: if the returned list contains the QgsFeatureRequest::AllAttributes constant then all attributes from the layer are required for evaluation of the expression. QgsFeatureRequest::setSubsetOfAttributes automatically handles this case.

bool QgsExpression::registerFunction ( QgsExpression::Function * function )

static

QString QgsExpression::replaceExpressionText	(	const QString &	action,
		const QgsFeature *	feat,
		QgsVectorLayer *	layer,
		const QMap< QString, QVariant > *	substitutionMap = `0`,
		const QgsDistanceArea *	distanceArea = `0`
	)

static

This function currently replaces each expression between [% and %] in the string with the result of its evaluation on the feature passed as argument.

Additional substitutions can be passed through the substitutionMap parameter

Parameters

action
feat
layer
substitutionMap
distanceArea	optional QgsDistanceArea. If specified, the QgsDistanceArea is used for distance and area conversion

const Node* QgsExpression::rootNode ( ) const

inline

Returns root node of the expression. Root node is null is parsing has failed.

double QgsExpression::scale ( )

inline

void QgsExpression::setCurrentRowNumber ( int rowNumber )

inline

Set the number for $rownum special column.

void QgsExpression::setEvalErrorString ( QString str )

inline

Set evaluation error (used internally by evaluation functions)

void QgsExpression::setGeomCalculator ( const QgsDistanceArea & calc )

Sets the geometry calculator used in evaluation of expressions,.

void QgsExpression::setScale ( double scale )

inline

void QgsExpression::setSpecialColumn	(	const QString &	name,
		QVariant	value
	)

static

Assign a special column.

QVariant QgsExpression::specialColumn ( const QString & name )

static

Return the value of the given special column or a null QVariant if undefined.

QList< QgsExpression::Function * > QgsExpression::specialColumns ( )

static

Returns a list of special Column definitions.

bool QgsExpression::unregisterFunction ( QString name )

static

void QgsExpression::unsetSpecialColumn ( const QString & name )

static

Unset a special column.

Friends And Related Function Documentation

friend class QgsOgcUtils

friend

Member Data Documentation

const char * QgsExpression::BinaryOperatorText

static

Initial value:

{
  "OR", "AND",
  "=", "<>", "<=", ">=", "<", ">", "~", "LIKE", "NOT LIKE", "ILIKE", "NOT ILIKE", "IS", "IS NOT",
  "+", "-", "*", "/", "%", "^",
  "||"
}

QHash< QString, QString > QgsExpression::gFunctionHelpTexts

staticprotected

QHash< QString, QString > QgsExpression::gGroups

staticprotected

QStringList QgsExpression::gmBuiltinFunctions

static

QList< QgsExpression::Function * > QgsExpression::gmFunctions

static

QMap< QString, QString > QgsExpression::gmSpecialColumnGroups

staticprotected

QMap< QString, QVariant > QgsExpression::gmSpecialColumns

staticprotected

QgsDistanceArea* QgsExpression::mCalc

protected

QString QgsExpression::mEvalErrorString

protected

QString QgsExpression::mExp

protected

QString QgsExpression::mParserErrorString

protected

Node* QgsExpression::mRootNode

protected

int QgsExpression::mRowNumber

protected

double QgsExpression::mScale

protected

const char * QgsExpression::UnaryOperatorText

static

Initial value:

{
  "NOT", "-"
}

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

/tmp/buildd/qgis-2.6.0+wheezy1/src/core/qgsexpression.h
/tmp/buildd/qgis-2.6.0+wheezy1/src/core/qgsexpression.cpp
/tmp/buildd/qgis-2.6.0+wheezy1/src/core/qgsexpression_texts.cpp

Classes

Public Types

Public Member Functions

Static Public Member Functions

Static Public Attributes

Protected Member Functions

Static Protected Member Functions

Protected Attributes

Static Protected Attributes

Friends

Detailed Description

Member Typedef Documentation

Member Enumeration Documentation

Constructor & Destructor Documentation

Member Function Documentation

Friends And Related Function Documentation

Member Data Documentation