[feature] Expression performance improvements

qgis · May 2, 2017 · 8d8fa94 · 8d8fa94 · NathanW2 · May 2, 2017
2 parents fbd62be + c30d7b9
commit 8d8fa94
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Showing 12 changed files with 576 additions and 95 deletions.
diff --git a/python/core/qgsexpression.sip b/python/core/qgsexpression.sip
@@ -570,7 +570,31 @@ Does this function use a geometry object.
 %Docstring
  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 **
+ Functions are non lazy default and will be given the node return value when called.
+ :rtype: bool
+%End
+
+        virtual bool isStatic( const QgsExpression::NodeFunction *node, QgsExpression *parent, const QgsExpressionContext *context ) const;
+%Docstring
+ Will be called during prepare to determine if the function is static.
+ A function is static if it will return the same value for every feature with different
+ attributes and/or geometry.
+
+ By default this will return true, if all arguments that have been passed to the function
+ are also static.
+
+.. versionadded:: 3.0
+ :rtype: bool
+%End
+
+        virtual bool prepare( const QgsExpression::NodeFunction *node, QgsExpression *parent, const QgsExpressionContext *context ) const;
+%Docstring
+ This will be called during the prepare step() of an expression if it is not static.
+
+ This can be used by functions to do any preparation steps that might help to speedup the upcoming
+ evaluation.
+
+.. versionadded:: 3.0
  :rtype: bool
 %End
 
@@ -643,6 +667,22 @@ The help text for the function.
  :rtype: bool
 %End
 
+      protected:
+
+        static bool allParamsStatic( const QgsExpression::NodeFunction *node, QgsExpression *parent, const QgsExpressionContext *context );
+%Docstring
+ This will return true if all the params for the provided function ``node`` are static within the
+ constraints imposed by the ``context`` within the given ``parent``.
+
+ This can be used as callback for custom implementations of subclasses. It is the default for implementation
+ for StaticFunction.isStatic.
+
+.. note::
+
+   Added in QGIS 3.0
+ :rtype: bool
+%End
+
     };
 
 
@@ -823,8 +863,6 @@ return index of the function in Functions array
         virtual QgsExpression::Node *clone() const = 0;
 %Docstring
  Generate a clone of this node.
- Make sure that the clone does not contain any information which is
- generated in prepare and context related.
  Ownership is transferred to the caller.
 
  :return: a deep copy of this node.
@@ -883,6 +921,19 @@ return index of the function in Functions array
  :rtype: bool
 %End
 
+
+      protected:
+
+        void cloneTo( QgsExpression::Node *target ) const;
+%Docstring
+ Needs to be called by all subclasses as part of their clone() implementation.
+
+.. note::
+
+   Not available in python bindings
+.. versionadded:: 3.0
+%End
+
       private:
         virtual bool prepareNode( QgsExpression *parent, const QgsExpressionContext *context ) = 0 ;
 %Docstring

diff --git a/python/core/qgsexpressioncontext.sip b/python/core/qgsexpressioncontext.sip
@@ -76,7 +76,7 @@ class QgsExpressionContextScope
        * @param value initial variable value
        * @param readOnly true if variable should not be editable by users
        */
-      StaticVariable( const QString &name = QString(), const QVariant &value = QVariant(), bool readOnly = false );
+      StaticVariable( const QString &name = QString(), const QVariant &value = QVariant(), bool readOnly = false, bool isStatic = false  );
 
       /** Variable name */
       QString name;
@@ -86,6 +86,9 @@ class QgsExpressionContextScope
 
       /** True if variable should not be editable by users */
       bool readOnly;
+
+      //! A static variable can be cached for the lifetime of a context
+      bool isStatic;
     };
 
     /** Constructor for QgsExpressionContextScope
@@ -109,7 +112,7 @@ class QgsExpressionContextScope
      * @param value variable value
      * @see addVariable()
      */
-    void setVariable( const QString &name, const QVariant &value );
+    void setVariable( const QString &name, const QVariant &value, bool isStatic = false );
 
     /** Adds a variable into the context scope. If a variable with the same name is already set then its
      * value is overwritten, otherwise a new variable is added to the scope.
@@ -162,6 +165,14 @@ class QgsExpressionContextScope
      */
     bool isReadOnly( const QString &name ) const;
 
+    /**
+     * Tests whether the variable with the specified \a name is static and can
+     * be cached.
+     *
+     * \note Added in QGIS 3.0
+     */
+    bool isStatic( const QString &name ) const;
+
     /** Returns the count of variables contained within the scope.
      */
     int variableCount() const;

diff --git a/python/core/qgsfeaturerequest.sip b/python/core/qgsfeaturerequest.sip
@@ -83,6 +83,15 @@ class QgsFeatureRequest
          */
         QgsExpression expression() const;
 
+        /**
+         * Prepare the expression with the given context.
+         *
+         * \see QgsExpression::prepare
+         *
+         * \since QGIS 3.0
+         */
+        bool prepare( QgsExpressionContext *context );
+
         /**
          * Order ascending
          * @return If ascending order is requested