Generic expression compiler for translation to provider specific SQL WHERE clauses. More...

#include <qgssqlexpressioncompiler.h>

Public Types
enum	Flag { CaseInsensitiveStringMatch = 1 , LikeIsCaseInsensitive = 1 << 1 , NoNullInBooleanLogic = 1 << 2 , NoUnaryMinus = 1 << 3 , IntegerDivisionResultsInInteger = 1 << 4 }
	Enumeration of flags for how provider handles SQL clauses. More...

typedef QFlags< Flag >	Flags

enum	Result { None , Complete , Partial , Fail }
	Possible results from expression compilation. More...

Public Member Functions
	QgsSqlExpressionCompiler (const QgsFields &fields, QgsSqlExpressionCompiler::Flags flags=Flags(), bool ignoreStaticNodes=false)
	Constructor for expression compiler.

virtual	~QgsSqlExpressionCompiler ()=default

virtual Result	compile (const QgsExpression *exp)
	Compiles an expression and returns the result of the compilation.

bool	opIsStringComparison (QgsExpressionNodeBinaryOperator::BinaryOperator op)
	Returns `true` if op is one of.

virtual QString	result ()
	Returns the compiled expression string for use by the provider.

Protected Member Functions
virtual QString	castToInt (const QString &value) const
	Casts a value to a integer result.

virtual QString	castToReal (const QString &value) const
	Casts a value to a real result.

virtual QString	castToText (const QString &value) const
	Casts a value to a text result.

virtual Result	compileNode (const QgsExpressionNode *node, QString &str)
	Compiles an expression node and returns the result of the compilation.

virtual QString	quotedIdentifier (const QString &identifier)
	Returns a quoted column identifier, in the format expected by the provider.

virtual QString	quotedValue (const QVariant &value, bool &ok)
	Returns a quoted attribute value, in the format expected by the provider.

virtual Result	replaceNodeByStaticCachedValueIfPossible (const QgsExpressionNode *node, QString &str)
	Tries to replace a node by its static cached value where possible.

virtual QStringList	sqlArgumentsFromFunctionName (const QString &fnName, const QStringList &fnArgs) const
	Returns the Arguments for SQL function for the expression function.

virtual QString	sqlFunctionFromFunctionName (const QString &fnName) const
	Returns the SQL function for the expression function.

Protected Attributes
QgsFields	mFields

QString	mResult

Detailed Description

Generic expression compiler for translation to provider specific SQL WHERE clauses.

This class is designed to be overridden by providers to take advantage of expression compilation, so that feature requests can take advantage of the provider's native filtering support.

Note: Not part of stable API, may change in future versions of QGIS; Not available in Python bindings

Definition at line 39 of file qgssqlexpressioncompiler.h.

Member Typedef Documentation

◆ Flags

typedef QFlags< Flag > QgsSqlExpressionCompiler::Flags

Definition at line 63 of file qgssqlexpressioncompiler.h.

Member Enumeration Documentation

◆ Flag

enum QgsSqlExpressionCompiler::Flag

Enumeration of flags for how provider handles SQL clauses.

Enumerator
CaseInsensitiveStringMatch	Provider performs case-insensitive string matching for all strings.
LikeIsCaseInsensitive	Provider treats LIKE as case-insensitive.
NoNullInBooleanLogic	Provider does not support using NULL with boolean logic, e.g., "(...) OR NULL".
NoUnaryMinus	Provider does not unary minus, e.g., " -( 100 * 2 ) = ...".
IntegerDivisionResultsInInteger	Dividing int by int results in int on provider. Subclass must implement the castToReal() function to allow compilation of division.

Definition at line 55 of file qgssqlexpressioncompiler.h.

◆ Result

enum QgsSqlExpressionCompiler::Result

Possible results from expression compilation.

Enumerator
None	No expression.
Complete	Expression was successfully compiled and can be completely delegated to provider.
Partial	Expression was partially compiled, but provider will return extra records and results must be double-checked using QGIS' expression engine.
Fail	Provider cannot handle expression.

Definition at line 44 of file qgssqlexpressioncompiler.h.

Constructor & Destructor Documentation

◆ QgsSqlExpressionCompiler()

QgsSqlExpressionCompiler::QgsSqlExpressionCompiler	(	const QgsFields &	fields,
		QgsSqlExpressionCompiler::Flags	flags = `Flags()`,
		bool	ignoreStaticNodes = `false`
	)

explicit

Constructor for expression compiler.

Parameters

fields	fields from provider
flags	flags which control how expression is compiled
ignoreStaticNodes	If an expression has been partially precalculated due to static nodes in the expression, setting this argument to `false` will prevent these precalculated values from being utilized during compilation of the expression. This flag significantly limits the effectiveness of compilation and should be used for debugging purposes only. (Since QGIS 3.18)

Definition at line 22 of file qgssqlexpressioncompiler.cpp.

◆ ~QgsSqlExpressionCompiler()

virtual QgsSqlExpressionCompiler::~QgsSqlExpressionCompiler ( )

virtualdefault

Member Function Documentation

◆ castToInt()

QString QgsSqlExpressionCompiler::castToInt ( const QString & value ) const

protectedvirtual

Casts a value to a integer result.

Subclasses must reimplement this to cast a numeric value to a integer type value so that integer division results in a integer value result instead of real.

Definition at line 540 of file qgssqlexpressioncompiler.cpp.

◆ castToReal()

QString QgsSqlExpressionCompiler::castToReal ( const QString & value ) const

protectedvirtual

Casts a value to a real result.

Subclasses which indicate the IntegerDivisionResultsInInteger flag must reimplement this to cast a numeric value to a real type value so that division results in a real value result instead of integer.

Definition at line 529 of file qgssqlexpressioncompiler.cpp.

◆ castToText()

QString QgsSqlExpressionCompiler::castToText ( const QString & value ) const

protectedvirtual

Casts a value to a text result.

Subclasses that support casting to text may implement this function to get equal behavior to the QGIS expression engine when string comparison operators are applied on non-string data.

Example

579 LIKE '5%'

which on a postgres database needs to be

579::text LIKE '5%'

Since: QGIS 3.2

Definition at line 535 of file qgssqlexpressioncompiler.cpp.

◆ compile()

QgsSqlExpressionCompiler::Result QgsSqlExpressionCompiler::compile ( const QgsExpression * exp )

virtual

Compiles an expression and returns the result of the compilation.

Definition at line 29 of file qgssqlexpressioncompiler.cpp.

◆ compileNode()

QgsSqlExpressionCompiler::Result QgsSqlExpressionCompiler::compileNode	(	const QgsExpressionNode *	node,
		QString &	str
	)

protectedvirtual

Compiles an expression node and returns the result of the compilation.

Parameters

node	expression node to compile
str	string representing compiled node should be stored in this parameter

Returns: result of node compilation

Definition at line 90 of file qgssqlexpressioncompiler.cpp.

◆ opIsStringComparison()

bool QgsSqlExpressionCompiler::opIsStringComparison ( QgsExpressionNodeBinaryOperator::BinaryOperator op )

Returns true if op is one of.

LIKE
ILIKE
NOT LIKE
NOT ILIKE
~ (regexp)

In such cases the left operator will be cast to string to behave equal to QGIS own expression engine.

Since: QGIS 3.2

Definition at line 42 of file qgssqlexpressioncompiler.cpp.

◆ quotedIdentifier()

QString QgsSqlExpressionCompiler::quotedIdentifier ( const QString & identifier )

protectedvirtual

Returns a quoted column identifier, in the format expected by the provider.

Derived classes should override this if special handling of column identifiers is required.

See also: quotedValue()

Definition at line 54 of file qgssqlexpressioncompiler.cpp.

◆ quotedValue()

QString QgsSqlExpressionCompiler::quotedValue	(	const QVariant &	value,
		bool &	ok
	)

protectedvirtual

Returns a quoted attribute value, in the format expected by the provider.

Derived classes should override this if special handling of attribute values is required.

Parameters

value	value to quote
ok	will be set to `true` if value can be compiled

See also: quotedIdentifier()

Definition at line 62 of file qgssqlexpressioncompiler.cpp.

◆ replaceNodeByStaticCachedValueIfPossible()

QgsSqlExpressionCompiler::Result QgsSqlExpressionCompiler::replaceNodeByStaticCachedValueIfPossible	(	const QgsExpressionNode *	node,
		QString &	str
	)

protectedvirtual

Tries to replace a node by its static cached value where possible.

Since: QGIS 3.18

Definition at line 546 of file qgssqlexpressioncompiler.cpp.

◆ result()

QString QgsSqlExpressionCompiler::result ( )

virtual

Returns the compiled expression string for use by the provider.

Definition at line 37 of file qgssqlexpressioncompiler.cpp.

◆ sqlArgumentsFromFunctionName()

QStringList QgsSqlExpressionCompiler::sqlArgumentsFromFunctionName	(	const QString &	fnName,
		const QStringList &	fnArgs
	)		const

protectedvirtual

Returns the Arguments for SQL function for the expression function.

Derived classes should override this to help compile functions

Parameters

fnName	expression function name
fnArgs	arguments from expression

Returns: the arguments updated for SQL Function

Definition at line 523 of file qgssqlexpressioncompiler.cpp.

◆ sqlFunctionFromFunctionName()

QString QgsSqlExpressionCompiler::sqlFunctionFromFunctionName ( const QString & fnName ) const

protectedvirtual

Returns the SQL function for the expression function.

Derived classes should override this to help compile functions

Parameters

fnName expression function name

Returns: the SQL function name

Definition at line 517 of file qgssqlexpressioncompiler.cpp.

Member Data Documentation

◆ mFields

QgsFields QgsSqlExpressionCompiler::mFields

protected

Definition at line 184 of file qgssqlexpressioncompiler.h.

◆ mResult

QString QgsSqlExpressionCompiler::mResult

protected

Definition at line 183 of file qgssqlexpressioncompiler.h.

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

/build/qgis-3.41.0+git20241225+af5edcb665c+99sid/src/core/qgssqlexpressioncompiler.h
/build/qgis-3.41.0+git20241225+af5edcb665c+99sid/src/core/qgssqlexpressioncompiler.cpp

Public Types

Public Member Functions

Protected Member Functions

Protected Attributes

Detailed Description

Member Typedef Documentation

◆ Flags

Member Enumeration Documentation

◆ Flag

◆ Result

Constructor & Destructor Documentation

◆ QgsSqlExpressionCompiler()

◆ ~QgsSqlExpressionCompiler()

Member Function Documentation

◆ castToInt()

◆ castToReal()

◆ castToText()

Example

◆ compile()

◆ compileNode()

◆ opIsStringComparison()

◆ quotedIdentifier()

◆ quotedValue()

◆ replaceNodeByStaticCachedValueIfPossible()

◆ result()

◆ sqlArgumentsFromFunctionName()

◆ sqlFunctionFromFunctionName()

Member Data Documentation

◆ mFields

◆ mResult