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qgsexpressionnode.h
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qgsexpressionnode.h
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/***************************************************************************
qgsexpressionnode.h
-------------------
begin : May 2017
copyright : (C) 2017 Matthias Kuhn
email : matthias@opengis.ch
***************************************************************************
* *
* This program is free software; you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
* the Free Software Foundation; either version 2 of the License, or *
* (at your option) any later version. *
* *
***************************************************************************/
#ifndef QGSEXPRESSIONNODE_H
#define QGSEXPRESSIONNODE_H
#include <QSet>
#include <QVariant>
#include <QCoreApplication>
#include "qgis.h"
class QgsExpression;
class QgsExpressionContext;
/**
* \ingroup core
*
* Abstract base class for all nodes that can appear in an expression.
*/
class CORE_EXPORT QgsExpressionNode SIP_ABSTRACT
{
#ifdef SIP_RUN
SIP_CONVERT_TO_SUBCLASS_CODE
switch ( sipCpp->nodeType() )
{
case QgsExpressionNode::ntUnaryOperator:
sipType = sipType_QgsExpressionNodeUnaryOperator;
break;
case QgsExpressionNode::ntBinaryOperator:
sipType = sipType_QgsExpressionNodeBinaryOperator;
break;
case QgsExpressionNode::ntInOperator:
sipType = sipType_QgsExpressionNodeInOperator;
break;
case QgsExpressionNode::ntFunction:
sipType = sipType_QgsExpressionNodeFunction;
break;
case QgsExpressionNode::ntLiteral:
sipType = sipType_QgsExpressionNodeLiteral;
break;
case QgsExpressionNode::ntColumnRef:
sipType = sipType_QgsExpressionNodeColumnRef;
break;
case QgsExpressionNode::ntCondition:
sipType = sipType_QgsExpressionNodeCondition;
break;
default:
sipType = 0;
break;
}
SIP_END
#endif
Q_DECLARE_TR_FUNCTIONS( QgsExpressionNode );
public:
enum NodeType
{
ntUnaryOperator, //!< \see QgsExpression::Node::NodeUnaryOperator
ntBinaryOperator, //!< \see QgsExpression::Node::NodeBinaryOperator
ntInOperator, //!< \see QgsExpression::Node::NodeInOperator
ntFunction, //!< \see QgsExpression::Node::NodeFunction
ntLiteral, //!< \see QgsExpression::Node::NodeLiteral
ntColumnRef, //!< \see QgsExpression::Node::NodeColumnRef
ntCondition //!< \see QgsExpression::Node::NodeCondition
};
//! Named node
//! \since QGIS 2.16
//! \ingroup core
struct NamedNode
{
public:
/** Constructor for NamedNode
* \param name node name
* \param node node
*/
NamedNode( const QString &name, QgsExpressionNode *node )
: name( name )
, node( node )
{}
//! Node name
QString name;
//! Node
QgsExpressionNode *node = nullptr;
};
/** \ingroup core
*/
class CORE_EXPORT NodeList
{
public:
virtual ~NodeList();
//! Takes ownership of the provided node
void append( QgsExpressionNode *node SIP_TRANSFER ) { mList.append( node ); mNameList.append( QString() ); }
/** Adds a named node. Takes ownership of the provided node.
* \since QGIS 2.16
*/
void append( QgsExpressionNode::NamedNode *node SIP_TRANSFER );
/** Returns the number of nodes in the list.
*/
int count() const { return mList.count(); }
//! Returns true if list contains any named nodes
//! \since QGIS 2.16
bool hasNamedNodes() const { return mHasNamedNodes; }
/**
* Get a list of all the nodes.
*/
QList<QgsExpressionNode *> list() { return mList; }
/**
* Get the node at position i in the list.
*
* \since QGIS 3.0
*/
QgsExpressionNode *at( int i ) { return mList.at( i ); }
//! Returns a list of names for nodes. Unnamed nodes will be indicated by an empty string in the list.
//! \since QGIS 2.16
QStringList names() const { return mNameList; }
//! Creates a deep copy of this list. Ownership is transferred to the caller
NodeList *clone() const;
virtual QString dump() const;
private:
QList<QgsExpressionNode *> mList;
QStringList mNameList;
bool mHasNamedNodes = false;
public:
};
virtual ~QgsExpressionNode() = default;
/**
* Get the type of this node.
*
* \returns The type of this node
*/
virtual QgsExpressionNode::NodeType nodeType() const = 0;
/**
* 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.
*/
virtual QString dump() const = 0;
/**
* Evaluate this node with the given context and parent.
* This will return a cached value if it has been determined to be static
* during the prepare() execution.
*
* \since QGIS 2.12
*/
QVariant eval( QgsExpression *parent, const QgsExpressionContext *context );
/**
* Generate a clone of this node.
* Ownership is transferred to the caller.
*
* \returns a deep copy of this node.
*/
virtual QgsExpressionNode *clone() const = 0;
/**
* 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.
*
* \returns A list of columns required to evaluate this expression
*/
virtual QSet<QString> referencedColumns() const = 0;
/**
* Return a set of all variables which are used in this expression.
*/
virtual QSet<QString> referencedVariables() const = 0;
/**
* 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
*/
virtual bool needsGeometry() const = 0;
/**
* 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
*/
virtual bool isStatic( QgsExpression *parent, const QgsExpressionContext *context ) const = 0;
/**
* Prepare this node for evaluation.
* This will check if the node content is static and in this case cache the value.
* If it's not static it will call prepareNode() to allow the node to do initialization
* work like for example resolving a column name to an attribute index.
*
* \since QGIS 2.12
*/
bool prepare( QgsExpression *parent, const QgsExpressionContext *context );
protected:
/**
* Copies the members of this node to the node provided in \a target.
* Needs to be called by all subclasses as part of their clone() implementation.
*
* \note Not available in python bindings, QgsExpression::Node is not
* going to be subclassed from python. If that's what you are looking
* for, look into writing a custom python expression function.
* \since QGIS 3.0
*/
void cloneTo( QgsExpressionNode *target ) const SIP_SKIP;
private:
/**
* Abstract virtual preparation method
* Errors are reported to the parent
* \since QGIS 3.0
*/
virtual bool prepareNode( QgsExpression *parent, const QgsExpressionContext *context ) = 0;
/**
* Abstract virtual eval method
* Errors are reported to the parent
* \since QGIS 3.0
*/
virtual QVariant evalNode( QgsExpression *parent, const QgsExpressionContext *context ) = 0;
bool mHasCachedValue = false;
QVariant mCachedStaticValue;
};
Q_DECLARE_METATYPE( QgsExpressionNode * )
#endif // QGSEXPRESSIONNODE_H