Add lazy evaluation support to expression functions

NathanW2 · NathanW2 · commit d61bf1f70f5a · 2014-12-13T15:33:09.000+10:00
Add if(cond, true, false) function using lazy evaluation feature
diff --git a/src/core/qgsexpression.cpp b/src/core/qgsexpression.cpp
@@ -338,6 +338,15 @@ static QgsFeature getFeature( const QVariant& value, QgsExpression* parent )
   return 0;
 }
 
+static QgsExpression::Node* getNode( const QVariant& value, QgsExpression* parent )
+{
+  if ( value.canConvert<QgsExpression::Node*>() )
+    return value.value<QgsExpression::Node*>();
+
+  parent->setEvalErrorString( "Cannot convert to Node" );
+  return 0;
+}
+
 // this handles also NULL values
 static TVL getTVLValue( const QVariant& value, QgsExpression* parent )
 {
@@ -1355,6 +1364,27 @@ static QVariant fcnColorRgb( const QVariantList &values, const QgsFeature *, Qgs
   return QString( "%1,%2,%3" ).arg( color.red() ).arg( color.green() ).arg( color.blue() );
 }
 
+static QVariant fcnIf( const QVariantList &values, const QgsFeature *f, QgsExpression *parent )
+{
+  QgsExpression::Node* node = getNode( values.at( 0 ), parent );
+  ENSURE_NO_EVAL_ERROR;
+  QVariant value = node->eval( parent, f );
+  ENSURE_NO_EVAL_ERROR;
+  if ( value.toBool() ) {
+    node = getNode( values.at( 1 ), parent );
+    ENSURE_NO_EVAL_ERROR;
+    value = node->eval( parent, f );
+    ENSURE_NO_EVAL_ERROR;
+  }
+  else {
+    node = getNode( values.at( 2 ), parent );
+    ENSURE_NO_EVAL_ERROR;
+    value = node->eval( parent, f );
+    ENSURE_NO_EVAL_ERROR;
+  }
+  return value;
+}
+
 static QVariant fncColorRgba( const QVariantList &values, const QgsFeature *, QgsExpression *parent )
 {
   int red = getIntValue( values.at( 0 ), parent );
@@ -1660,6 +1690,7 @@ const QList<QgsExpression::Function*> &QgsExpression::Functions()
     << new StaticFunction( "totime", 1, fcnToTime, "Conversions" )
     << new StaticFunction( "tointerval", 1, fcnToInterval, "Conversions" )
     << new StaticFunction( "coalesce", -1, fcnCoalesce, "Conditionals" )
+    << new StaticFunction( "if", 3, fcnIf, "Conditionals", "", False, QStringList(), true )
     << new StaticFunction( "regexp_match", 2, fcnRegexpMatch, "Conditionals" )
     << new StaticFunction( "$now", 0, fcnNow, "Date and Time" )
     << new StaticFunction( "age", 2, fcnAge, "Date and Time" )
@@ -2533,10 +2564,17 @@ QVariant QgsExpression::NodeFunction::eval( QgsExpression* parent, const QgsFeat
   {
     foreach ( Node* n, mArgs->list() )
     {
-      QVariant v = n->eval( parent, f );
-      ENSURE_NO_EVAL_ERROR;
-      if ( isNull( v ) && fd->name() != "coalesce" )
-        return QVariant(); // all "normal" functions return NULL, when any parameter is NULL (so coalesce is abnormal)
+      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, f );
+        ENSURE_NO_EVAL_ERROR;
+        if ( isNull( v ) && fd->name() != "coalesce" )
+                return QVariant(); // all "normal" functions return NULL, when any parameter is NULL (so coalesce is abnormal)
+      }
       argValues.append( v );
     }
   }
diff --git a/src/core/qgsexpression.h b/src/core/qgsexpression.h
@@ -282,15 +282,20 @@ class CORE_EXPORT QgsExpression
     class CORE_EXPORT Function
     {
       public:
-        Function( QString fnname, int params, QString group, QString helpText = QString(), bool usesGeometry = false, QStringList referencedColumns = QStringList() )
-            : mName( fnname ), mParams( params ), mUsesGeometry( usesGeometry ), mGroup( group ), mHelpText( helpText ), mReferencedColumns( referencedColumns ) {}
+        Function( QString fnname, int params, QString group, QString helpText = QString(), bool usesGeometry = false, QStringList referencedColumns = QStringList(), bool lazyEval = false )
+            : mName( fnname ), mParams( params ), mUsesGeometry( usesGeometry ), mGroup( group ), mHelpText( helpText ), mReferencedColumns( referencedColumns ), mLazyEval( lazyEval ) {}
         /** The name of the function. */
         QString name() { return mName; }
         /** The number of parameters this function takes. */
         int params() { return mParams; }
         /** Does this function use a geometry object. */
         bool usesgeometry() { return mUsesGeometry; }
 
+        /** True if this function should use lazy evaluation.  Lazy evaluation functions take QgsExpression::Node objects
+         * rather than the node results when called.  You can use node->eval(parent, feature) to evaluate the node and return the result
+         * Functions are non lazy default and will be given the node return value when called **/
+        bool lazyEval() { return mLazyEval; }
+
         virtual QStringList referencedColumns() const { return mReferencedColumns; }
 
         /** The group the function belongs to. */
@@ -315,13 +320,14 @@ class CORE_EXPORT QgsExpression
         QString mGroup;
         QString mHelpText;
         QStringList mReferencedColumns;
+        bool mLazyEval;
     };
 
     class StaticFunction : public Function
     {
       public:
-        StaticFunction( QString fnname, int params, FcnEval fcn, QString group, QString helpText = QString(), bool usesGeometry = false, QStringList referencedColumns = QStringList() )
-            : Function( fnname, params, group, helpText, usesGeometry, referencedColumns ), mFnc( fcn ) {}
+        StaticFunction( QString fnname, int params, FcnEval fcn, QString group, QString helpText = QString(), bool usesGeometry = false, QStringList referencedColumns = QStringList(), bool lazyEval = false )
+            : Function( fnname, params, group, helpText, usesGeometry, referencedColumns, lazyEval ), mFnc( fcn ) {}
 
         virtual QVariant func( const QVariantList& values, const QgsFeature* f, QgsExpression* parent )
         {
@@ -680,5 +686,6 @@ class CORE_EXPORT QgsExpression
 };
 
 Q_DECLARE_METATYPE( QgsExpression::Interval );
+Q_DECLARE_METATYPE( QgsExpression::Node* );
 
 #endif // QGSEXPRESSION_H
diff --git a/tests/src/core/testqgsexpression.cpp b/tests/src/core/testqgsexpression.cpp
@@ -377,6 +377,8 @@ class TestQgsExpression: public QObject
       QTest::newRow( "regexp match invalid" ) << "regexp_match('abc DEF','[[[')" << true << QVariant();
       QTest::newRow( "regexp match escaped" ) << "regexp_match('abc DEF','\\\\s[A-Z]+')" << false << QVariant( 1 );
       QTest::newRow( "regexp match false" ) << "regexp_match('abc DEF','\\\\s[a-z]+')" << false << QVariant( 0 );
+      QTest::newRow( "if true" ) << "if(1=1, 1, 0)" << false << QVariant( 1 );
+      QTest::newRow( "if false" ) << "if(1=2, 1, 0)" << false << QVariant( 0 );
 
       // Datetime functions
       QTest::newRow( "to date" ) << "todate('2012-06-28')" << false << QVariant( QDate( 2012, 6, 28 ) );
