Add fast truncate implementation for memory provider

nyalldawson · nyalldawson · commit fd0fba70c1ea · 2018-12-27T18:06:35.000+10:00
diff --git a/src/core/providers/memory/qgsmemoryprovider.cpp b/src/core/providers/memory/qgsmemoryprovider.cpp
@@ -616,9 +616,16 @@ QgsVectorDataProvider::Capabilities QgsMemoryProvider::capabilities() const
 {
   return AddFeatures | DeleteFeatures | ChangeGeometries |
          ChangeAttributeValues | AddAttributes | DeleteAttributes | RenameAttributes | CreateSpatialIndex |
-         SelectAtId | CircularGeometries;
+         SelectAtId | CircularGeometries | FastTruncate;
 }
 
+bool QgsMemoryProvider::truncate()
+{
+  mFeatures.clear();
+  clearMinMaxCache();
+  mExtent.setMinimal();
+  return true;
+}
 
 void QgsMemoryProvider::updateExtents()
 {
diff --git a/src/core/providers/memory/qgsmemoryprovider.h b/src/core/providers/memory/qgsmemoryprovider.h
@@ -68,6 +68,7 @@ class QgsMemoryProvider : public QgsVectorDataProvider
     bool supportsSubsetString() const override { return true; }
     bool createSpatialIndex() override;
     QgsVectorDataProvider::Capabilities capabilities() const override;
+    bool truncate() override;
 
     /* Implementation of functions from QgsDataProvider */
 

Original file line number	Diff line number	Diff line change
`@@ -616,9 +616,16 @@ QgsVectorDataProvider::Capabilities QgsMemoryProvider::capabilities() const`
`616`	`616`	`{`
`617`	`617`	`return AddFeatures \| DeleteFeatures \| ChangeGeometries \|`
`618`	`618`	`ChangeAttributeValues \| AddAttributes \| DeleteAttributes \| RenameAttributes \| CreateSpatialIndex \|`
`619`		`- SelectAtId \| CircularGeometries;`
	`619`	`+ SelectAtId \| CircularGeometries \| FastTruncate;`
`620`	`620`	`}`
`621`	`621`
	`622`	`+bool QgsMemoryProvider::truncate()`
	`623`	`+{`
	`624`	`+ mFeatures.clear();`
	`625`	`+ clearMinMaxCache();`
	`626`	`+ mExtent.setMinimal();`
	`627`	`+ return true;`
	`628`	`+}`
`622`	`629`
`623`	`630`	`void QgsMemoryProvider::updateExtents()`
`624`	`631`	`{`