Use ad-hoc WHERE clause for TopoGeometry layers

This is aimed at using spatial indexes on primitive tables.
Only affects non-hierarchical TopoGeometry layers access.

Thanks Laurențiu Nicola (grayshade) for excellent feedback and
Salvatore Fiandaca (pigreco) for testing !

src/providers/postgres/qgspostgresfeatureiterator.cpp

@@ -506,10 +506,54 @@ QString QgsPostgresFeatureIterator::whereClauseRect()
   bool castToGeometry = mSource->mSpatialColType == SctGeography ||
                         mSource->mSpatialColType == SctPcPatch;
 
-  QString whereClause = QStringLiteral( "%1%2 && %3" )
-                        .arg( QgsPostgresConn::quotedIdentifier( mSource->mBoundingBoxColumn ),
-                              castToGeometry ? "::geometry" : "",
-                              qBox );
+  QString whereClause;
+  if ( mSource->mSpatialColType == SctTopoGeometry &&
+       mSource->mTopoLayerInfo.layerLevel == 0 )
+  {
+    whereClause = QStringLiteral( R"SQL(
+      id(%1) in (
+        WITH elems AS (
+
+          SELECT n.node_id id, 1 typ
+          FROM %3.node n
+          WHERE %5 in (1,4) AND n.geom && %2
+
+            UNION ALL
+
+          SELECT edge_id, 2
+          FROM %3.edge
+          WHERE %5 in (2,4) AND geom && %2
+
+            UNION ALL
+
+          SELECT face_id, 3
+          FROM %3.face
+          WHERE %5 in (3,4) AND mbr && %2
+
+        )
+        select r.topogeo_id
+        FROM %3.relation r, elems e
+        WHERE r.layer_id = %4
+          AND r.element_type = e.typ
+          AND r.element_id = e.id
+      )
+    )SQL" )
+                  // Should we bother with mBoundingBoxColumn ?
+                  .arg(
+                    QgsPostgresConn::quotedIdentifier( mSource->mGeometryColumn ),
+                    qBox,
+                    QgsPostgresConn::quotedIdentifier( mSource->mTopoLayerInfo.topologyName )
+                  )
+                  .arg( mSource->mTopoLayerInfo.layerId )
+                  .arg( mSource->mTopoLayerInfo.featureType );
+  }
+  else
+  {
+    whereClause = QStringLiteral( "%1%2 && %3" )
+                  .arg( QgsPostgresConn::quotedIdentifier( mSource->mBoundingBoxColumn ),
+                        castToGeometry ? "::geometry" : "",
+                        qBox );
+  }
 
   // For geography type, using a && filter with the geography column cast as
   // geometry prevents the use of a spatial index. So for "small" filtering
@@ -1034,6 +1078,7 @@ QgsPostgresFeatureSource::QgsPostgresFeatureSource( const QgsPostgresProvider *p
   , mQuery( p->mQuery )
   , mCrs( p->crs() )
   , mShared( p->mShared )
+  , mTopoLayerInfo( p->mTopoLayerInfo )
 {
   if ( mSqlWhereClause.startsWith( QLatin1String( " WHERE " ) ) )
     mSqlWhereClause = mSqlWhereClause.mid( 7 );

src/providers/postgres/qgspostgresfeatureiterator.h

@@ -63,6 +63,8 @@ class QgsPostgresFeatureSource final: public QgsAbstractFeatureSource
      * connection has since been destroyed. */
     QgsPostgresConn *mTransactionConnection = nullptr;
 
+    QgsPostgresProvider::TopoLayerInfo mTopoLayerInfo;
+
     friend class QgsPostgresFeatureIterator;
     friend class QgsPostgresExpressionCompiler;
 };

src/providers/postgres/qgspostgresprovider.cpp

@@ -2403,10 +2403,19 @@ QString QgsPostgresProvider::paramValue( const QString &fieldValue, const QStrin
 /* private */
 bool QgsPostgresProvider::getTopoLayerInfo()
 {
-  QString sql = QString( "SELECT t.name, l.layer_id "
-                         "FROM topology.layer l, topology.topology t "
-                         "WHERE l.topology_id = t.id AND l.schema_name=%1 "
-                         "AND l.table_name=%2 AND l.feature_column=%3" )
+  QString sql = QStringLiteral( R"SQL(
+    SELECT
+      t.name,
+      l.layer_id,
+      l.level,
+      l.feature_type
+    FROM topology.layer l
+    JOIN topology.topology t ON (
+      l.topology_id = t.id
+    )
+    WHERE l.schema_name=%1
+    AND l.table_name=%2 AND l.feature_column=%3
+  )SQL" )
                 .arg( quotedValue( mSchemaName ),
                       quotedValue( mTableName ),
                       quotedValue( mGeometryColumn ) );
@@ -2426,6 +2435,23 @@ bool QgsPostgresProvider::getTopoLayerInfo()
   }
   mTopoLayerInfo.topologyName = result.PQgetvalue( 0, 0 );
   mTopoLayerInfo.layerId = result.PQgetvalue( 0, 1 ).toLong();
+  mTopoLayerInfo.layerLevel = result.PQgetvalue( 0, 2 ).toInt();
+  switch ( result.PQgetvalue( 0, 3 ).toInt() )
+  {
+    case 1:
+      mTopoLayerInfo.featureType = TopoLayerInfo::Puntal;
+      break;
+    case 2:
+      mTopoLayerInfo.featureType = TopoLayerInfo::Lineal;
+      break;
+    case 3:
+      mTopoLayerInfo.featureType = TopoLayerInfo::Polygonal;
+      break;
+    case 4:
+    default:
+      mTopoLayerInfo.featureType = TopoLayerInfo::Mixed;
+      break;
+  }
   return true;
 }
 

src/providers/postgres/qgspostgresprovider.h

@@ -432,6 +432,14 @@ class QgsPostgresProvider final: public QgsVectorDataProvider
     {
       QString topologyName;
       long    layerId;
+      int     layerLevel;
+      enum TopoFeatureType
+      {
+        Puntal = 1,
+        Lineal = 2,
+        Polygonal = 3,
+        Mixed = 4
+      } featureType;
     };
 
     TopoLayerInfo mTopoLayerInfo;