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[FEATURE] Add an eval expression

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Funded by
 * Regional Council of Picardy
 * ADUGA
 * Ville de Nyon
 * Wetu GIT cc
This commit is contained in:
Matthias Kuhn 2015-12-07 19:00:51 +01:00
parent 6035d98b4a
commit f961ecef46
3 changed files with 51 additions and 0 deletions
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10
resources/function_help/json/eval Normal file
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@ -0,0 +1,10 @@
{
"name": "eval",
"type": "function",
"description": "Evaluates an expression which is passed in a string. Useful to expand dynamic parameters passed as context variables or fields.",
"arguments": [ {"arg":"expression","description":"an expression string"}],
"examples": [
{ "expression":"eval('\\'nice\\'')", "returns":"'nice'"},
{ "expression":"eval(@expression_var)", "returns":"[whatever the result of evaluating @expression_var might be...]"}
]
}

11
src/core/qgsexpression.cpp
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@ -409,6 +409,16 @@ static QVariant fcnGetVariable( const QVariantList& values, const QgsExpressionC
return context->variable( name );
}
static QVariant fcnEval( const QVariantList& values, const QgsExpressionContext* context, QgsExpression* parent )
{
if ( !context )
return QVariant();
QString expString = getStringValue( values.at( 0 ), parent );
QgsExpression expression( expString );
return expression.evaluate( context );
}
static QVariant fcnSqrt( const QVariantList& values, const QgsExpressionContext*, QgsExpression* parent )
{
double x = getDoubleValue( values.at( 0 ), parent );
@ -2522,6 +2532,7 @@ const QList<QgsExpression::Function*>& QgsExpression::Functions()
//return all attributes string for referencedColumns - this is caught by
// QgsFeatureRequest::setSubsetOfAttributes and causes all attributes to be fetched by the
// feature request
<< new StaticFunction( "eval", 1, fcnEval, "General", QString(), true, QStringList( QgsFeatureRequest::AllAttributes ) )
<< new StaticFunction( "attribute", 2, fcnAttribute, "Record", QString(), false, QStringList( QgsFeatureRequest::AllAttributes ) )
<< new StaticFunction( "_specialcol_", 1, fcnSpecialColumn, "Special" )

30
tests/src/core/testqgsexpression.cpp
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@ -1530,6 +1530,36 @@ class TestQgsExpression: public QObject
Q_NOWARN_DEPRECATED_POP
}
void eval_eval()
{
QgsFeature f( 100 );
QgsFields fields;
fields.append( QgsField( "col1" ) );
fields.append( QgsField( "second_column", QVariant::Int ) );
f.setFields( fields, true );
f.setAttribute( QString( "col1" ), QString( "test value" ) );
f.setAttribute( QString( "second_column" ), 5 );
QgsExpressionContext context = QgsExpressionContextUtils::createFeatureBasedContext( f, QgsFields() );
QgsExpression exp1( "eval()" );
QVariant v1 = exp1.evaluate( &context );
Q_ASSERT( !v1.isValid() );
QgsExpression exp2( "eval('4')" );
QVariant v2 = exp2.evaluate( &context );
QCOMPARE( v2, QVariant( 4 ) );
QgsExpression exp3( "eval('\"second_column\" * 2')" );
QVariant v3 = exp3.evaluate( &context );
QCOMPARE( v3, QVariant( 10 ) );
QgsExpression exp4( "eval('\"col1\"')" );
QVariant v4 = exp4.evaluate( &context );
QCOMPARE( v4, QVariant( "test value" ) );
}
void expression_from_expression_data()
{
QTest::addColumn<QString>( "string" );