/************************************************************************ * This file has been generated automatically from * * * * src/core/expression/qgsexpression.h * * * * Do not edit manually ! Edit header and run scripts/sipify.pl again * ************************************************************************/ class QgsExpression { %Docstring Class for parsing and evaluation of expressions (formerly called "search strings"). The expressions try to follow both syntax and semantics of SQL expressions. Usage: \code{.cpp} 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 } \endcode Three Value Logic ================= 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: NULL QVariant. Performance =========== 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 a 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 to_int, to_real, to_string 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. Implicit sharing ================ This class is implicitly shared, copying has a very low overhead. It is normally preferable to call `QgsExpression( otherExpression )` instead of `QgsExpression( otherExpression.expression() )`. A deep copy will only be made when prepare() is called. For usage this means mainly, that you should normally keep an unprepared master copy of a QgsExpression and whenever using it with a particular QgsFeatureIterator copy it just before and prepare it using the same context as the iterator. Implicit sharing was added in 2.14 %End %TypeHeaderCode #include "qgsexpression.h" %End public: QgsExpression( const QString &expr ); %Docstring Creates a new expression based on the provided string. The string will immediately be parsed. For optimization prepare() should always be called before every loop in which this expression is used. %End QgsExpression( const QgsExpression &other ); %Docstring Create a copy of this expression. This is preferred over recreating an expression from a string since it does not need to be re-parsed. %End QgsExpression(); %Docstring Create an empty expression. .. versionadded:: 3.0 %End ~QgsExpression(); bool operator==( const QgsExpression &other ) const; bool isValid() const; %Docstring Checks if this expression is valid. A valid expression could be parsed but does not necessarily evaluate properly. .. versionadded:: 3.0 :rtype: bool %End bool hasParserError() const; %Docstring Returns true if an error occurred when parsing the input expression :rtype: bool %End QString parserErrorString() const; %Docstring Returns parser error :rtype: str %End const QgsExpressionNode *rootNode() const; %Docstring Returns root node of the expression. Root node is null is parsing has failed :rtype: QgsExpressionNode %End bool prepare( const QgsExpressionContext *context ); %Docstring Get the expression ready for evaluation - find out column indexes. \param context context for preparing expression .. versionadded:: 2.12 :rtype: bool %End QSet referencedColumns() const; %Docstring 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. .. seealso:: referencedAttributeIndexes() :rtype: set of str %End QSet referencedVariables() const; %Docstring Return a list of all variables which are used in this expression. If the list contains a NULL QString, there is a variable name used which is determined at runtime. .. versionadded:: 3.0 :rtype: set of str %End QSet referencedAttributeIndexes( const QgsFields &fields ) const; %Docstring Return a list of field name indexes obtained from the provided fields. .. versionadded:: 3.0 :rtype: set of int %End bool needsGeometry() const; %Docstring Returns true if the expression uses feature geometry for some computation :rtype: bool %End QVariant evaluate(); %Docstring Evaluate the feature and return the result. .. note:: this method does not expect that prepare() has been called on this instance .. versionadded:: 2.12 :rtype: QVariant %End QVariant evaluate( const QgsExpressionContext *context ); %Docstring Evaluate the expression against the specified context and return the result. \param context context for evaluating expression .. note:: prepare() should be called before calling this method. .. versionadded:: 2.12 :rtype: QVariant %End bool hasEvalError() const; %Docstring Returns true if an error occurred when evaluating last input :rtype: bool %End QString evalErrorString() const; %Docstring Returns evaluation error :rtype: str %End void setEvalErrorString( const QString &str ); %Docstring Set evaluation error (used internally by evaluation functions) %End bool isField() const; %Docstring Checks whether an expression consists only of a single field reference .. versionadded:: 2.9 :rtype: bool %End static bool checkExpression( const QString &text, const QgsExpressionContext *context, QString &errorMessage /Out/ ); %Docstring Tests whether a string is a valid expression. \param text string to test \param context optional expression context \param errorMessage will be filled with any error message from the validation :return: true if string is a valid expression .. versionadded:: 2.12 :rtype: bool %End void setExpression( const QString &expression ); %Docstring Set the expression string, will reset the whole internal structure. .. versionadded:: 3.0 %End QString expression() const; %Docstring API calls, dump() will be used to create one instead. :rtype: str %End QString dump() const; %Docstring expression() instead. :rtype: str %End QgsDistanceArea *geomCalculator(); %Docstring Return calculator used for distance and area calculations (used by $length, $area and $perimeter functions only) .. seealso:: setGeomCalculator() .. seealso:: distanceUnits() .. seealso:: areaUnits() :rtype: QgsDistanceArea %End void setGeomCalculator( const QgsDistanceArea *calc ); %Docstring Sets the geometry calculator used for distance and area calculations in expressions. (used by $length, $area and $perimeter functions only). By default, no geometry calculator is set and all distance and area calculations are performed using simple cartesian methods (ie no ellipsoidal calculations). \param calc geometry calculator. Ownership is not transferred. Set to a None to force cartesian calculations. .. seealso:: geomCalculator() %End QgsUnitTypes::DistanceUnit distanceUnits() const; %Docstring Returns the desired distance units for calculations involving geomCalculator(), e.g., "$length" and "$perimeter". .. note:: distances are only converted when a geomCalculator() has been set .. versionadded:: 2.14 .. seealso:: setDistanceUnits() .. seealso:: areaUnits() :rtype: QgsUnitTypes.DistanceUnit %End void setDistanceUnits( QgsUnitTypes::DistanceUnit unit ); %Docstring Sets the desired distance units for calculations involving geomCalculator(), e.g., "$length" and "$perimeter". .. note:: distances are only converted when a geomCalculator() has been set .. versionadded:: 2.14 .. seealso:: distanceUnits() .. seealso:: setAreaUnits() %End QgsUnitTypes::AreaUnit areaUnits() const; %Docstring Returns the desired areal units for calculations involving geomCalculator(), e.g., "$area". .. note:: areas are only converted when a geomCalculator() has been set .. versionadded:: 2.14 .. seealso:: setAreaUnits() .. seealso:: distanceUnits() :rtype: QgsUnitTypes.AreaUnit %End void setAreaUnits( QgsUnitTypes::AreaUnit unit ); %Docstring Sets the desired areal units for calculations involving geomCalculator(), e.g., "$area". .. note:: areas are only converted when a geomCalculator() has been set .. versionadded:: 2.14 .. seealso:: areaUnits() .. seealso:: setDistanceUnits() %End static QString replaceExpressionText( const QString &action, const QgsExpressionContext *context, const QgsDistanceArea *distanceArea = 0 ); %Docstring This function replaces each expression between [% and %] in the string with the result of its evaluation with the specified context Additional substitutions can be passed through the substitutionMap parameter \param action The source string in which placeholders should be replaced. \param context Expression context \param distanceArea Optional QgsDistanceArea. If specified, the QgsDistanceArea is used for distance and area conversion .. versionadded:: 2.12 :rtype: str %End static double evaluateToDouble( const QString &text, const double fallbackValue ); %Docstring Attempts to evaluate a text string as an expression to a resultant double value. \param text text to evaluate as expression \param fallbackValue value to return if text can not be evaluated as a double :return: evaluated double value, or fallback value .. versionadded:: 2.7 .. note:: this method is inefficient for bulk evaluation of expressions, it is intended for one-off evaluations only. :rtype: float %End enum SpatialOperator { soBbox, soIntersects, soContains, soCrosses, soEquals, soDisjoint, soOverlaps, soTouches, soWithin, }; static const QList &Functions(); %Docstring :rtype: list of QgsExpressionFunction %End static const QStringList &BuiltinFunctions(); %Docstring :rtype: list of str %End static bool registerFunction( QgsExpressionFunction *function, bool transferOwnership = false ); %Docstring Registers a function to the expression engine. This is required to allow expressions to utilize the function. \param function function to register \param transferOwnership set to true to transfer ownership of function to expression engine :return: true on successful registration .. seealso:: unregisterFunction :rtype: bool %End static bool unregisterFunction( const QString &name ); %Docstring Unregisters a function from the expression engine. The function will no longer be usable in expressions. \param name function name .. seealso:: registerFunction :rtype: bool %End static void cleanRegisteredFunctions(); %Docstring Deletes all registered functions whose ownership have been transferred to the expression engine. .. versionadded:: 2.12 %End static bool isFunctionName( const QString &name ); %Docstring tells whether the identifier is a name of existing function :rtype: bool %End static int functionIndex( const QString &name ); %Docstring return index of the function in Functions array :rtype: int %End static int functionCount(); %Docstring Returns the number of functions defined in the parser :return: The number of function defined in the parser. :rtype: int %End static QString quotedColumnRef( QString name ); %Docstring Returns a quoted column reference (in double quotes) .. seealso:: quotedString() .. seealso:: quotedValue() :rtype: str %End static QString quotedString( QString text ); %Docstring Returns a quoted version of a string (in single quotes) .. seealso:: quotedValue() .. seealso:: quotedColumnRef() :rtype: str %End static QString quotedValue( const QVariant &value ); %Docstring Returns a string representation of a literal value, including appropriate quotations where required. \param value value to convert to a string representation .. versionadded:: 2.14 .. seealso:: quotedString() .. seealso:: quotedColumnRef() :rtype: str %End static QString quotedValue( const QVariant &value, QVariant::Type type ); %Docstring Returns a string representation of a literal value, including appropriate quotations where required. \param value value to convert to a string representation \param type value type .. versionadded:: 2.14 .. seealso:: quotedString() .. seealso:: quotedColumnRef() :rtype: str %End static QString helpText( QString name ); %Docstring Returns the help text for a specified function. \param name function name .. seealso:: variableHelpText() :rtype: str %End static QString variableHelpText( const QString &variableName, bool showValue = true, const QVariant &value = QVariant() ); %Docstring Returns the help text for a specified variable. \param variableName name of variable \param showValue set to true to include current value of variable in help text \param value current value of variable to show in help text .. seealso:: helpText() .. versionadded:: 2.12 :rtype: str %End static QString group( const QString &group ); %Docstring Returns the translated name for a function group. \param group untranslated group name :rtype: str %End static QString formatPreviewString( const QVariant &value ); %Docstring Formats an expression result for friendly display to the user. Truncates the result to a sensible length, and presents text representations of non numeric/text types (e.g., geometries and features). \param value expression result to format :return: formatted string, may contain HTML formatting characters .. versionadded:: 2.14 :rtype: str %End static QString createFieldEqualityExpression( const QString &fieldName, const QVariant &value ); %Docstring Create an expression allowing to evaluate if a field is equal to a value. The value may be null. \param fieldName the name of the field \param value the value of the field :return: the expression to evaluate field equality .. versionadded:: 3.0 :rtype: str %End }; /************************************************************************ * This file has been generated automatically from * * * * src/core/expression/qgsexpression.h * * * * Do not edit manually ! Edit header and run scripts/sipify.pl again * ************************************************************************/