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[FEATURE] Add with_variable function

This function sets a variable for parts of an expression, therefore
avoiding to repeatedly recalculate complex values.
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m-kuhn committed Jul 7, 2017
1 parent 9562536 commit efff5f1670712d447ec8f8ac9a7951b5ff687825
@@ -249,6 +249,11 @@ The help text for the function.
:rtype: QVariant
%End

virtual QVariant run( QgsExpressionNode::NodeList *args, const QgsExpressionContext *context, QgsExpression *parent );
%Docstring
:rtype: QVariant
%End

bool operator==( const QgsExpressionFunction &other ) const;

virtual bool handlesNull() const;
@@ -47,6 +47,34 @@ const QString QgsExpressionFunction::helpText() const
return mHelpText.isEmpty() ? QgsExpression::helpText( mName ) : mHelpText;
}

QVariant QgsExpressionFunction::run( QgsExpressionNode::NodeList *args, const QgsExpressionContext *context, QgsExpression *parent )
{
// evaluate arguments
QVariantList argValues;
if ( args )
{
Q_FOREACH ( QgsExpressionNode *n, args->list() )
{
QVariant v;
if ( lazyEval() )
{
// Pass in the node for the function to eval as it needs.
v = QVariant::fromValue( n );
}
else
{
v = n->eval( parent, context );
ENSURE_NO_EVAL_ERROR;
if ( QgsExpressionUtils::isNull( v ) && !handlesNull() )
return QVariant(); // all "normal" functions return NULL, when any QgsExpressionFunction::Parameter is NULL (so coalesce is abnormal)
}
argValues.append( v );
}
}

return func( argValues, context, parent );
}

bool QgsExpressionFunction::usesGeometry( const QgsExpressionNodeFunction *node ) const
{
Q_UNUSED( node )
@@ -4202,6 +4230,7 @@ const QList<QgsExpressionFunction *> &QgsExpression::Functions()

sFunctions
<< new QgsStaticExpressionFunction( QStringLiteral( "env" ), 1, fcnEnvVar, QStringLiteral( "General" ), QString() )
<< new QgsSetVariableExpressionFunction()
<< new QgsStaticExpressionFunction( QStringLiteral( "attribute" ), 2, fcnAttribute, QStringLiteral( "Record" ), QString(), false, QSet<QString>() << QgsFeatureRequest::ALL_ATTRIBUTES )

// functions for arrays
@@ -4246,3 +4275,92 @@ const QList<QgsExpressionFunction *> &QgsExpression::Functions()
}
return sFunctions;
}

QgsSetVariableExpressionFunction::QgsSetVariableExpressionFunction()
: QgsExpressionFunction( "set_variable", 3, QCoreApplication::tr( "General" ), "help text TODODOODO" )
{

}

bool QgsSetVariableExpressionFunction::isStatic( const QgsExpressionNodeFunction *node, QgsExpression *parent, const QgsExpressionContext *context ) const
{
bool isStatic = false;

QgsExpressionNode::NodeList *args = node->args();

if ( args->count() < 3 )
return false;

if ( args->at( 0 )->isStatic( parent, context ) && args->at( 1 )->isStatic( parent, context ) )
{
QVariant name = args->at( 0 )->eval( parent, context );
QVariant value = args->at( 1 )->eval( parent, context );

QgsExpressionContextScope *scope = new QgsExpressionContextScope();
scope->setVariable( name.toString(), value );

QgsExpressionContext *updatedContext = const_cast<QgsExpressionContext *>( context );
updatedContext->appendScope( scope );

if ( args->at( 3 )->isStatic( parent, updatedContext ) )
isStatic = true;
updatedContext->popScope();
}

return false;
}

QVariant QgsSetVariableExpressionFunction::run( QgsExpressionNode::NodeList *args, const QgsExpressionContext *context, QgsExpression *parent )
{
QVariant result;

if ( args->count() < 3 )
// error
return result;

QVariant name = args->at( 0 )->eval( parent, context );
QVariant value = args->at( 1 )->eval( parent, context );

QgsExpressionContextScope *scope = new QgsExpressionContextScope();
scope->setVariable( name.toString(), value );

QgsExpressionContext *updatedContext = const_cast<QgsExpressionContext *>( context );
updatedContext->appendScope( scope );
result = args->at( 2 )->eval( parent, updatedContext );
delete updatedContext->popScope();

return result;
}

QVariant QgsSetVariableExpressionFunction::func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent )
{
// This is a dummy function, all the real handling is in run
Q_UNUSED( values )
Q_UNUSED( context )
Q_UNUSED( parent )

Q_ASSERT( false );
return QVariant();
}

bool QgsSetVariableExpressionFunction::prepare( const QgsExpressionNodeFunction *node, QgsExpression *parent, const QgsExpressionContext *context ) const
{
QgsExpressionNode::NodeList *args = node->args();

if ( args->count() < 3 )
// error
return false;

QVariant name = args->at( 0 )->prepare( parent, context );
QVariant value = args->at( 1 )->prepare( parent, context );

QgsExpressionContextScope *scope = new QgsExpressionContextScope();
scope->setVariable( name.toString(), value );

QgsExpressionContext *updatedContext = const_cast<QgsExpressionContext *>( context );
updatedContext->appendScope( scope );
args->at( 2 )->prepare( parent, updatedContext );
delete updatedContext->popScope();

return true;
}
@@ -24,6 +24,7 @@

#include "qgis.h"
#include "qgis_core.h"
#include "qgsexpressionnode.h"

class QgsExpressionNodeFunction;
class QgsExpression;
@@ -273,6 +274,8 @@ class CORE_EXPORT QgsExpressionFunction
*/
virtual QVariant func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent ) = 0;

virtual QVariant run( QgsExpressionNode::NodeList *args, const QgsExpressionContext *context, QgsExpression *parent );

bool operator==( const QgsExpressionFunction &other ) const;

virtual bool handlesNull() const;
@@ -451,6 +454,21 @@ class QgsStaticExpressionFunction : public QgsExpressionFunction
QSet<QString> mReferencedColumns;
bool mIsStatic = false;
};

class QgsSetVariableExpressionFunction : public QgsExpressionFunction
{
public:
QgsSetVariableExpressionFunction();

bool isStatic( const QgsExpressionNodeFunction *node, QgsExpression *parent, const QgsExpressionContext *context ) const override;

QVariant run( QgsExpressionNode::NodeList *args, const QgsExpressionContext *context, QgsExpression *parent ) override;

QVariant func( const QVariantList &values, const QgsExpressionContext *context, QgsExpression *parent ) override;

bool prepare( const QgsExpressionNodeFunction *node, QgsExpression *parent, const QgsExpressionContext *context ) const override;
};

#endif

#endif // QGSEXPRESSIONFUNCTION_H
@@ -842,31 +842,7 @@ QVariant QgsExpressionNodeFunction::evalNode( QgsExpression *parent, const QgsEx
QString name = QgsExpression::QgsExpression::Functions()[mFnIndex]->name();
QgsExpressionFunction *fd = context && context->hasFunction( name ) ? context->function( name ) : QgsExpression::QgsExpression::Functions()[mFnIndex];

// evaluate arguments
QVariantList argValues;
if ( mArgs )
{
Q_FOREACH ( QgsExpressionNode *n, mArgs->list() )
{
QVariant v;
if ( fd->lazyEval() )
{
// Pass in the node for the function to eval as it needs.
v = QVariant::fromValue( n );
}
else
{
v = n->eval( parent, context );
ENSURE_NO_EVAL_ERROR;
if ( QgsExpressionUtils::isNull( v ) && !fd->handlesNull() )
return QVariant(); // all "normal" functions return NULL, when any QgsExpressionFunction::Parameter is NULL (so coalesce is abnormal)
}
argValues.append( v );
}
}

// run the function
QVariant res = fd->func( argValues, context, parent );
QVariant res = fd->run( mArgs, context, parent );
ENSURE_NO_EVAL_ERROR;

// everything went fine

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