Feature simplification for oracle provider

Author: ahuarte47

src/providers/oracle/qgsoraclefeatureiterator.cpp

@@ -148,6 +148,27 @@ bool QgsOracleFeatureIterator::nextFeatureFilterExpression( QgsFeature& f )
     return fetchFeature( f );
 }
 
+bool QgsOracleFeatureIterator::prepareSimplification( const QgsSimplifyMethod& simplifyMethod )
+{
+  // setup simplification of geometries to fetch
+  if ( !( mRequest.flags() & QgsFeatureRequest::NoGeometry ) &&
+       simplifyMethod.methodType() != QgsSimplifyMethod::NoSimplification &&
+       !simplifyMethod.forceLocalOptimization() )
+  {
+    QgsSimplifyMethod::MethodType methodType = simplifyMethod.methodType();
+
+    if ( methodType == QgsSimplifyMethod::OptimizeForRendering )
+    {
+      return true;
+    }
+    else
+    {
+      QgsDebugMsg( QString( "Simplification method type (%1) is not recognised by OracleFeatureIterator" ).arg( methodType ) );
+    }
+  }
+  return QgsAbstractFeatureIterator::prepareSimplification( simplifyMethod );
+}
+
 bool QgsOracleFeatureIterator::fetchFeature( QgsFeature& feature )
 {
   feature.setValid( false );
@@ -316,7 +337,20 @@ bool QgsOracleFeatureIterator::openQuery( QString whereClause )
 
     if (( mRequest.flags() & QgsFeatureRequest::NoGeometry ) == 0 && !mSource->mGeometryColumn.isNull() )
     {
-      query += QgsOracleProvider::quotedIdentifier( mSource->mGeometryColumn );
+      if ( !mRequest.simplifyMethod().forceLocalOptimization() &&
+           mRequest.simplifyMethod().methodType() == QgsSimplifyMethod::OptimizeForRendering &&
+           QGis::flatType( QGis::singleType( mSource->mRequestedGeomType != QGis::WKBUnknown
+                                             ? mSource->mRequestedGeomType
+                                             : mSource->mDetectedGeomType ) ) != QGis::WKBPoint )
+      {
+        query += QString( "SDO_UTIL.SIMPLIFY( %1, %2 )" )
+                 .arg( QgsOracleProvider::quotedIdentifier( mSource->mGeometryColumn ) )
+                 .arg( mRequest.simplifyMethod().tolerance() * 0.7 ); //-> We use a smaller tolerance than pre-filtering to be on the safe side
+      }
+      else
+      {
+        query += QgsOracleProvider::quotedIdentifier( mSource->mGeometryColumn );
+      }
       delim = ",";
     }
 
@@ -377,6 +411,11 @@ bool QgsOracleFeatureIterator::openQuery( QString whereClause )
   return true;
 }
 
+bool QgsOracleFeatureIterator::providerCanSimplify( QgsSimplifyMethod::MethodType methodType ) const
+{
+  return methodType == QgsSimplifyMethod::OptimizeForRendering;
+}
+
 // -----------
 
 QgsOracleFeatureSource::QgsOracleFeatureSource( const QgsOracleProvider* p )

src/providers/oracle/qgsoraclefeatureiterator.h

@@ -76,13 +76,20 @@ class QgsOracleFeatureIterator : public QgsAbstractFeatureIteratorFromSource<Qgs
     //! fetch next feature filter expression
     bool nextFeatureFilterExpression( QgsFeature& f ) override;
 
+    //! Setup the simplification of geometries to fetch using the specified simplify method
+    virtual bool prepareSimplification( const QgsSimplifyMethod& simplifyMethod ) override;
+
     bool openQuery( QString whereClause );
 
     QgsOracleConn *mConnection;
     QSqlQuery mQry;
     bool mRewind;
     bool mExpressionCompiled;
     QgsAttributeList mAttributeList;
+
+  private:
+    //! returns whether the iterator supports simplify geometries on provider side
+    virtual bool providerCanSimplify( QgsSimplifyMethod::MethodType methodType ) const override;
 };
 
 #endif // QGSORACLEFEATUREITERATOR_H

src/providers/oracle/qgsoracleprovider.cpp

@@ -747,6 +747,9 @@ bool QgsOracleProvider::hasSufficientPermsAndCapabilities()
 
   mEnabledCapabilities = QgsVectorDataProvider::SelectAtId | QgsVectorDataProvider::SelectGeometryAtId;
 
+  // supports geometry simplification on provider side
+  mEnabledCapabilities |= QgsVectorDataProvider::SimplifyGeometries;
+
   QSqlQuery qry( *mConnection );
   if ( !mIsQuery )
   {