From ef6a7e5d9ff324e9ba69cb6ecbe710ded73beb23 Mon Sep 17 00:00:00 2001
From: Alessandro Pasotti <elpaso@itopen.it>
Date: Wed, 23 Sep 2020 15:31:12 +0200
Subject: [PATCH] Expose PG unrestricted empty tables as apatial items

also fix test
---
 .../postgres/qgspostgresdataitems.cpp         | 13 +++++--
 .../qgspostgresproviderconnection.cpp         | 34 +++++++++----------
 .../test_qgsproviderconnection_postgres.py    |  1 +
 3 files changed, 28 insertions(+), 20 deletions(-)

diff --git a/src/providers/postgres/qgspostgresdataitems.cpp b/src/providers/postgres/qgspostgresdataitems.cpp
index 746bd605884..538b54ca387 100644
--- a/src/providers/postgres/qgspostgresdataitems.cpp
+++ b/src/providers/postgres/qgspostgresdataitems.cpp
@@ -416,10 +416,16 @@ QVector<QgsDataItem *> QgsPGSchemaItem::createChildren()
     {
       if ( dontResolveType )
       {
-        //QgsDebugMsg( QStringLiteral( "skipping column %1.%2 without type constraint" ).arg( layerProperty.schemaName ).arg( layerProperty.tableName ) );
+        QgsDebugMsgLevel( QStringLiteral( "skipping column %1.%2 without type constraint" ).arg( layerProperty.schemaName ).arg( layerProperty.tableName ), 2 );
         continue;
       }
+      // If the table is empty there is no way we can retrieve layer types, let's make a copy and restore it
+      QgsPostgresLayerProperty propertyCopy { layerProperty };
       conn->retrieveLayerTypes( layerProperty, estimatedMetadata );
+      if ( layerProperty.size() == 0 )
+      {
+        layerProperty = propertyCopy;
+      }
     }
 
     for ( int i = 0; i < layerProperty.size(); i++ )
@@ -512,8 +518,9 @@ QgsPGLayerItem *QgsPGSchemaItem::createLayer( QgsPostgresLayerProperty layerProp
         break;
       default:
         if ( !layerProperty.geometryColName.isEmpty() )
-          return nullptr;
-
+        {
+          QgsDebugMsgLevel( QStringLiteral( "Adding layer item %1.%2 without type constraint as geometryless table" ).arg( layerProperty.schemaName ).arg( layerProperty.tableName ), 2 );
+        }
         layerType = QgsLayerItem::TableLayer;
         tip = tr( "as geometryless table" );
     }
diff --git a/src/providers/postgres/qgspostgresproviderconnection.cpp b/src/providers/postgres/qgspostgresproviderconnection.cpp
index 3d2255fb226..2e6ec459f46 100644
--- a/src/providers/postgres/qgspostgresproviderconnection.cpp
+++ b/src/providers/postgres/qgspostgresproviderconnection.cpp
@@ -671,32 +671,32 @@ QgsFields QgsPostgresProviderConnection::fields( const QString &schema, const QS
     // This table might expose multiple geometry columns (different geom type or SRID)
     // but we are only interested in fields here, so let's pick the first one.
     TableProperty tableInfo { table( schema, tableName ) };
-    if ( tableInfo.geometryColumnTypes().count( ) > 1 )
+    try
     {
-      try
+      QgsDataSourceUri tUri { tableUri( schema, tableName ) };
+      if ( tableInfo.geometryColumnTypes().count( ) > 1 )
       {
-        QgsDataSourceUri tUri { tableUri( schema, tableName ) };
         TableProperty::GeometryColumnType geomCol { tableInfo.geometryColumnTypes().first() };
         tUri.setGeometryColumn( tableInfo.geometryColumn() );
         tUri.setWkbType( geomCol.wkbType );
         tUri.setSrid( QString::number( geomCol.crs.postgisSrid() ) );
-        if ( tableInfo.primaryKeyColumns().count() > 0 )
-        {
-          tUri.setKeyColumn( tableInfo.primaryKeyColumns().first() );
-        }
-        tUri.setParam( QStringLiteral( "checkPrimaryKeyUnicity" ), QLatin1String( "0" ) );
-        QgsVectorLayer::LayerOptions options { false, true };
-        options.skipCrsValidation = true;
-        QgsVectorLayer vl { tUri.uri(), QStringLiteral( "temp_layer" ), mProviderKey, options };
-        if ( vl.isValid() )
-        {
-          return vl.fields();
-        }
       }
-      catch ( QgsProviderConnectionException & )
+      if ( tableInfo.primaryKeyColumns().count() > 0 )
       {
-        // fall-through
+        tUri.setKeyColumn( tableInfo.primaryKeyColumns().first() );
       }
+      tUri.setParam( QStringLiteral( "checkPrimaryKeyUnicity" ), QLatin1String( "0" ) );
+      QgsVectorLayer::LayerOptions options { false, true };
+      options.skipCrsValidation = true;
+      QgsVectorLayer vl { tUri.uri(), QStringLiteral( "temp_layer" ), mProviderKey, options };
+      if ( vl.isValid() )
+      {
+        return vl.fields();
+      }
+    }
+    catch ( QgsProviderConnectionException & )
+    {
+      // fall-through
     }
     throw ex;
   }
diff --git a/tests/src/python/test_qgsproviderconnection_postgres.py b/tests/src/python/test_qgsproviderconnection_postgres.py
index df6ef0267fa..5f2c92bb16c 100644
--- a/tests/src/python/test_qgsproviderconnection_postgres.py
+++ b/tests/src/python/test_qgsproviderconnection_postgres.py
@@ -334,6 +334,7 @@ IMPORT FOREIGN SCHEMA qgis_test LIMIT TO ( "someData" )
 
         md = QgsProviderRegistry.instance().providerMetadata('postgres')
         conn = md.createConnection(self.uri, {})
+        self.assertTrue(conn.tableExists('public', 'raster_columns'))
         fields = conn.fields("public", "raster_columns")
         self.assertEqual(fields.names(), [
             'r_table_catalog',