Allow properties/collections to be prepared in advance

python/core/qgsproperty.sip

@@ -69,6 +69,13 @@ class QgsAbstractProperty
      */
     void setActive( bool active );
 
+    /**
+     * Prepares the property against a specified expression context. Calling prepare before evaluating the
+     * property multiple times allows precalculation of expensive setup tasks such as parsing expressions.
+     * Returns true if preparation was successful.
+     */
+    virtual bool prepare( const QgsExpressionContext& context = QgsExpressionContext() ) const;
+
     /** Returns the set of any fields referenced by the property.
      * @param context expression context the property will be evaluated against.
      */
@@ -237,6 +244,7 @@ class QgsFieldBasedProperty : QgsAbstractProperty
      */
     QString field() const;
 
+    bool prepare( const QgsExpressionContext& context = QgsExpressionContext() ) const;
     virtual QSet< QString > referencedFields( const QgsExpressionContext& context = QgsExpressionContext() ) const;
 
     bool writeXml( QDomElement& propertyElem, QDomDocument& doc ) const;
@@ -283,6 +291,7 @@ class QgsExpressionBasedProperty : QgsAbstractProperty
      */
     QString expressionString() const;
 
+    bool prepare( const QgsExpressionContext& context = QgsExpressionContext() ) const;
     virtual QSet< QString > referencedFields( const QgsExpressionContext& context = QgsExpressionContext() ) const;
 
     bool writeXml( QDomElement& propertyElem, QDomDocument& doc ) const;

python/core/qgspropertycollection.sip

@@ -126,6 +126,13 @@ class QgsAbstractPropertyCollection
      */
     int valueAsInt( int key, const QgsExpressionContext& context, int defaultValue = 0 ) const;
 
+    /**
+     * Prepares the collection against a specified expression context. Calling prepare before evaluating the
+     * collection's properties multiple times allows precalculation of expensive setup tasks such as parsing expressions.
+     * Returns true if preparation was successful.
+     */
+    virtual bool prepare( const QgsExpressionContext& context = QgsExpressionContext() ) const = 0;
+
     /**
      * Returns the set of any fields referenced by the active properties from the collection.
      * @param context expression context the properties will be evaluated against.
@@ -215,6 +222,7 @@ class QgsPropertyCollection : QgsAbstractPropertyCollection
     bool hasProperty( int key ) const;
     QgsAbstractProperty* property( int key );
     QVariant value( int key, const QgsExpressionContext& context, const QVariant& defaultValue = QVariant() ) const;
+    bool prepare( const QgsExpressionContext& context = QgsExpressionContext() ) const;
     QSet< QString > referencedFields( const QgsExpressionContext& context = QgsExpressionContext() ) const;
     bool isActive( int key ) const;
     bool hasActiveProperties() const;
@@ -336,6 +344,8 @@ class QgsPropertyCollectionStack : QgsAbstractPropertyCollection
      */
     QVariant value( int key, const QgsExpressionContext& context, const QVariant& defaultValue = QVariant() ) const;
 
+    bool prepare( const QgsExpressionContext& context = QgsExpressionContext() ) const;
+
     /** Returns the set of any fields referenced by the active properties from the stack.
      * @param context expression context the properties will be evaluated against.
      */

src/core/qgsdiagramrenderer.cpp

@@ -143,6 +143,11 @@ void QgsDiagramLayerSettings::writeXml( QDomElement& layerElem, QDomDocument& do
   layerElem.appendChild( diagramLayerElem );
 }
 
+bool QgsDiagramLayerSettings::prepare( const QgsExpressionContext& context ) const
+{
+  return mProperties.prepare( context );
+}
+
 void QgsDiagramLayerSettings::init()
 {
   if ( sPropertyNameMap.isEmpty() )

src/core/qgsdiagramrenderer.h

@@ -241,6 +241,14 @@ class CORE_EXPORT QgsDiagramLayerSettings
     void readXml( const QDomElement& elem, const QgsVectorLayer* layer );
     void writeXml( QDomElement& layerElem, QDomDocument& doc, const QgsVectorLayer* layer ) const;
 
+    /**
+     * Prepares the diagrams for a specified expression context. Calling prepare before rendering
+     * multiple diagrams allows precalculation of expensive setup tasks such as parsing expressions.
+     * Returns true if preparation was successful.
+     * @note added in QGIS 3.0
+     */
+    bool prepare( const QgsExpressionContext& context = QgsExpressionContext() ) const;
+
     /** Returns the set of any fields referenced by the layer's diagrams.
      * @param context expression context the diagrams will be drawn using
      * @note added in QGIS 2.16

src/core/qgsproperty.cpp

@@ -233,8 +233,21 @@ bool QgsStaticProperty::readXml( const QDomElement &propertyElem, const QDomDocu
 QgsFieldBasedProperty::QgsFieldBasedProperty( const QString& field, bool isActive )
     : QgsAbstractProperty( isActive )
     , mField( field )
-{
+{}
 
+QgsFieldBasedProperty::QgsFieldBasedProperty( const QgsFieldBasedProperty& other )
+    : QgsAbstractProperty( other )
+    , mField( other.mField )
+    // don't copy cached field index!
+{}
+
+QgsFieldBasedProperty& QgsFieldBasedProperty::operator=( const QgsFieldBasedProperty & other )
+{
+  QgsAbstractProperty::operator=( other );
+  mActive = other.mActive;
+  mField = other.mField;
+  mCachedFieldIdx = -1;
+  return *this;
 }
 
 QgsFieldBasedProperty* QgsFieldBasedProperty::clone()
@@ -242,6 +255,17 @@ QgsFieldBasedProperty* QgsFieldBasedProperty::clone()
   return new QgsFieldBasedProperty( *this );
 }
 
+bool QgsFieldBasedProperty::prepare( const QgsExpressionContext& context ) const
+{
+  if ( !mActive )
+    return true;
+
+  // cache field index to avoid subsequent lookups
+  QgsFields f = context.fields();
+  mCachedFieldIdx = f.lookupField( mField );
+  return true;
+}
+
 QVariant QgsFieldBasedProperty::propertyValue( const QgsExpressionContext& context, const QVariant& defaultValue ) const
 {
   if ( !mActive )
@@ -251,6 +275,10 @@ QVariant QgsFieldBasedProperty::propertyValue( const QgsExpressionContext& conte
   if ( !f.isValid() )
     return defaultValue;
 
+  //shortcut the field lookup
+  if ( mCachedFieldIdx >= 0 )
+    return f.attribute( mCachedFieldIdx );
+
   int fieldIdx = f.fieldNameIndex( mField );
   if ( fieldIdx < 0 )
     return defaultValue;
@@ -296,7 +324,6 @@ bool QgsFieldBasedProperty::readXml( const QDomElement& propertyElem, const QDom
 QgsExpressionBasedProperty::QgsExpressionBasedProperty( const QString& expression, bool isActive )
     : QgsAbstractProperty( isActive )
     , mExpressionString( expression )
-    , mPrepared( false )
     , mExpression( expression )
 {
 

src/core/qgsproperty.h

@@ -93,6 +93,13 @@ class CORE_EXPORT QgsAbstractProperty
      */
     void setActive( bool active ) { mActive = active; }
 
+    /**
+     * Prepares the property against a specified expression context. Calling prepare before evaluating the
+     * property multiple times allows precalculation of expensive setup tasks such as parsing expressions.
+     * Returns true if preparation was successful.
+     */
+    virtual bool prepare( const QgsExpressionContext& context = QgsExpressionContext() ) const { Q_UNUSED( context ); return true; }
+
     /**
      * Returns the set of any fields referenced by the property.
      * @param context expression context the property will be evaluated against.
@@ -262,6 +269,13 @@ class CORE_EXPORT QgsFieldBasedProperty : public QgsAbstractProperty
      */
     QgsFieldBasedProperty( const QString& field = QString(), bool isActive = false );
 
+    /**
+     * Copy constructor
+     */
+    QgsFieldBasedProperty( const QgsFieldBasedProperty& other );
+
+    QgsFieldBasedProperty& operator=( const QgsFieldBasedProperty& other );
+
     virtual Type propertyType() const override { return FieldBasedProperty; }
 
     virtual QgsFieldBasedProperty* clone() override;
@@ -279,6 +293,7 @@ class CORE_EXPORT QgsFieldBasedProperty : public QgsAbstractProperty
      */
     QString field() const { return mField; }
 
+    bool prepare( const QgsExpressionContext& context = QgsExpressionContext() ) const override;
     virtual QSet< QString > referencedFields( const QgsExpressionContext& context = QgsExpressionContext() ) const override;
     bool writeXml( QDomElement& propertyElem, QDomDocument& doc ) const override;
     bool readXml( const QDomElement& propertyElem, const QDomDocument& doc ) override;
@@ -290,6 +305,7 @@ class CORE_EXPORT QgsFieldBasedProperty : public QgsAbstractProperty
   private:
 
     QString mField;
+    mutable int mCachedFieldIdx = -1;
 
 };
 
@@ -328,6 +344,7 @@ class CORE_EXPORT QgsExpressionBasedProperty : public QgsAbstractProperty
      */
     QString expressionString() const { return mExpressionString; }
 
+    bool prepare( const QgsExpressionContext& context = QgsExpressionContext() ) const override;
     virtual QSet< QString > referencedFields( const QgsExpressionContext& context = QgsExpressionContext() ) const override;
     bool writeXml( QDomElement& propertyElem, QDomDocument& doc ) const override;
     bool readXml( const QDomElement& propertyElem, const QDomDocument& doc ) override;
@@ -339,13 +356,11 @@ class CORE_EXPORT QgsExpressionBasedProperty : public QgsAbstractProperty
   private:
 
     QString mExpressionString;
-    mutable bool mPrepared;
+    mutable bool mPrepared = false;
     mutable QgsExpression mExpression;
     //! Cached set of referenced columns
     mutable QSet< QString > mReferencedCols;
 
-    bool prepare( const QgsExpressionContext& context ) const;
-
 };
 
 /**

src/core/qgspropertycollection.cpp

@@ -171,6 +171,20 @@ QVariant QgsPropertyCollection::value( int key, const QgsExpressionContext& cont
   return prop->value( context, defaultValue );
 }
 
+bool QgsPropertyCollection::prepare( const QgsExpressionContext& context ) const
+{
+  bool result = true;
+  QHash<int, QgsAbstractProperty*>::const_iterator it = mProperties.constBegin();
+  for ( ; it != mProperties.constEnd(); ++it )
+  {
+    if ( !it.value()->isActive() )
+      continue;
+
+    result = result && it.value()->prepare( context );
+  }
+  return result;
+}
+
 QSet< QString > QgsPropertyCollection::referencedFields( const QgsExpressionContext &context ) const
 {
   QSet< QString > cols;
@@ -439,6 +453,16 @@ QSet< QString > QgsPropertyCollectionStack::referencedFields( const QgsExpressio
   return cols;
 }
 
+bool QgsPropertyCollectionStack::prepare( const QgsExpressionContext& context ) const
+{
+  bool result = true;
+  Q_FOREACH ( QgsPropertyCollection* collection, mStack )
+  {
+    result = result && collection->prepare( context );
+  }
+  return result;
+}
+
 QSet<int> QgsPropertyCollectionStack::propertyKeys() const
 {
   QSet<int> keys;

src/core/qgspropertycollection.h

@@ -38,6 +38,8 @@ class CORE_EXPORT QgsAbstractPropertyCollection
 
     QgsAbstractPropertyCollection( const QString& name = QString() );
 
+    virtual ~QgsAbstractPropertyCollection() = default;
+
     /**
      * Returns the name of the property collection.
      * @see setName()
@@ -100,7 +102,6 @@ class CORE_EXPORT QgsAbstractPropertyCollection
      */
     virtual QVariant value( int key, const QgsExpressionContext& context, const QVariant& defaultValue = QVariant() ) const = 0;
 
-
     /**
      * Calculates the current value of the property with the specified key and interprets it as a color.
      * @param key integer key for property to return. The intended use case is that a context specific enum is cast to
@@ -140,6 +141,13 @@ class CORE_EXPORT QgsAbstractPropertyCollection
      */
     int valueAsInt( int key, const QgsExpressionContext& context, int defaultValue = 0 ) const;
 
+    /**
+     * Prepares the collection against a specified expression context. Calling prepare before evaluating the
+     * collection's properties multiple times allows precalculation of expensive setup tasks such as parsing expressions.
+     * Returns true if preparation was successful.
+     */
+    virtual bool prepare( const QgsExpressionContext& context = QgsExpressionContext() ) const = 0;
+
     /**
      * Returns the set of any fields referenced by the active properties from the collection.
      * @param context expression context the properties will be evaluated against.
@@ -231,6 +239,7 @@ class CORE_EXPORT QgsPropertyCollection : public QgsAbstractPropertyCollection
     QgsAbstractProperty* property( int key ) override;
     const QgsAbstractProperty* property( int key ) const override;
     QVariant value( int key, const QgsExpressionContext& context, const QVariant& defaultValue = QVariant() ) const override;
+    virtual bool prepare( const QgsExpressionContext& context = QgsExpressionContext() ) const override;
     QSet< QString > referencedFields( const QgsExpressionContext& context = QgsExpressionContext() ) const override;
     bool isActive( int key ) const override;
     bool hasActiveProperties() const override;
@@ -386,6 +395,7 @@ class CORE_EXPORT QgsPropertyCollectionStack : public QgsAbstractPropertyCollect
      * @param context expression context the properties will be evaluated against.
      */
     QSet< QString > referencedFields( const QgsExpressionContext& context = QgsExpressionContext() ) const override;
+    virtual bool prepare( const QgsExpressionContext& context = QgsExpressionContext() ) const override;
 
     QSet<int> propertyKeys() const override;
     bool hasProperty( int key ) const override;

src/core/qgsvectorlayerdiagramprovider.cpp

@@ -178,10 +178,12 @@ bool QgsVectorLayerDiagramProvider::prepare( const QgsRenderContext& context, QS
 
   s2.setRenderer( mDiagRenderer );
 
+  bool result = s2.prepare( context.expressionContext() );
+
   //add attributes needed by the diagram renderer
   attributeNames.unite( s2.referencedFields( context.expressionContext() ) );
 
-  return true;
+  return result;
 }
 
 

tests/src/core/testqgsproperty.cpp

@@ -318,6 +318,11 @@ void TestQgsProperty::fieldBasedProperty()
   QCOMPARE( defaultProperty.value( context, -1 ).toInt(), -1 );
   QVERIFY( defaultProperty.referencedFields( context ).isEmpty() );
 
+  //test preparation
+  QgsFieldBasedProperty property3( QString( "field1" ), true );
+  QVERIFY( property3.prepare( context ) );
+  QCOMPARE( property3.value( context, -1 ).toInt(), 5 );
+
   //saving and restoring
 
   //create a test dom element
@@ -411,6 +416,13 @@ void TestQgsProperty::expressionBasedProperty()
   QCOMPARE( defaultProperty.value( context, -1 ).toInt(), -1 );
   QVERIFY( defaultProperty.referencedFields( context ).isEmpty() );
 
+  //preparation
+  QgsExpressionBasedProperty property3( QString( "\"field1\" + \"field2\"" ), true );
+  QVERIFY( property3.prepare( context ) );
+  QCOMPARE( property3.value( context, -1 ).toInt(), 12 );
+  QgsExpressionBasedProperty property4( QString( "\"field1\" + " ), true );
+  QVERIFY( !property4.prepare( context ) );
+
   //saving and restoring
 
   //create a test dom element
@@ -776,6 +788,9 @@ void TestQgsProperty::propertyCollection()
   QVERIFY( collection.hasActiveProperties() );
   QVERIFY( !collection.hasActiveDynamicProperties() );
 
+  //preparation
+  QVERIFY( collection.prepare( context ) );
+
   //test bad property
   QVERIFY( !collection.property( Property2 ) );
   QVERIFY( !collection.value( Property2, context ).isValid() );
@@ -995,6 +1010,9 @@ void TestQgsProperty::collectionStack()
   QVERIFY( !stack.hasActiveDynamicProperties() );
   QVERIFY( stack.hasActiveProperties() );
 
+  //preparation
+  QVERIFY( stack.prepare( context ) );
+
   //test adding active property later in the stack
   QgsStaticProperty* property3 = new QgsStaticProperty( "value3", true );
   collection2->setProperty( Property1, property3 );