return the default style first in the list

python/core/auto_generated/qgsvectorlayer.sip.in

@@ -797,6 +797,10 @@ Lists all the style in db split into related to the layer and not related to
 :param msgError:
 
 :return: the number of styles related to current layer
+
+.. note::
+
+   Since QGIS 3.2 Styles related to the layer are ordered with the default style first then by update time for Postgres, MySQL and Spatialite.
 %End
 
     virtual QString getStyleFromDatabase( const QString &styleId, QString &msgError /Out/ );

src/core/qgsvectorlayer.h

@@ -800,6 +800,7 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionConte
      * \param descriptions the list in which will be stored the style descriptions
      * \param msgError
      * \returns the number of styles related to current layer
+     * \note Since QGIS 3.2 Styles related to the layer are ordered with the default style first then by update time for Postgres, MySQL and Spatialite.
      */
     virtual int listStylesInDatabase( QStringList &ids SIP_OUT, QStringList &names SIP_OUT,
                                       QStringList &descriptions SIP_OUT, QString &msgError SIP_OUT );

src/providers/mssql/qgsmssqlprovider.cpp

@@ -2244,7 +2244,8 @@ QGISEXTERN int listStyles( const QString &uri, QStringList &ids, QStringList &na
                                         " WHERE f_table_catalog=%1"
                                         " AND f_table_schema=%2"
                                         " AND f_table_name=%3"
-                                        " AND f_geometry_column=%4" )
+                                        " AND f_geometry_column=%4"
+                                        " ORDER BY useasdefault DESC, update_time DESC" )
                                .arg( QgsMssqlProvider::quotedValue( dsUri.database() ) )
                                .arg( QgsMssqlProvider::quotedValue( dsUri.schema() ) )
                                .arg( QgsMssqlProvider::quotedValue( dsUri.table() ) )

src/providers/postgres/qgspostgresprovider.cpp

@@ -4822,7 +4822,8 @@ QGISEXTERN int listStyles( const QString &uri, QStringList &ids, QStringList &na
                                         " WHERE f_table_catalog=%1"
                                         " AND f_table_schema=%2"
                                         " AND f_table_name=%3"
-                                        " AND f_geometry_column=%4" )
+                                        " AND f_geometry_column=%4"
+                                        " ORDER BY useasdefault DESC, update_time DESC" )
                                .arg( QgsPostgresConn::quotedValue( dsUri.database() ) )
                                .arg( QgsPostgresConn::quotedValue( dsUri.schema() ) )
                                .arg( QgsPostgresConn::quotedValue( dsUri.table() ) )

src/providers/spatialite/qgsspatialiteprovider.cpp

@@ -5836,7 +5836,8 @@ QGISEXTERN int listStyles( const QString &uri, QStringList &ids, QStringList &na
                                         " FROM layer_styles"
                                         " WHERE f_table_schema=%1"
                                         " AND f_table_name=%2"
-                                        " AND f_geometry_column=%3" )
+                                        " AND f_geometry_column=%3"
+                                        " ORDER BY useasdefault DESC, update_time DESC" )
                                .arg( QgsSpatiaLiteProvider::quotedValue( dsUri.schema() ) )
                                .arg( QgsSpatiaLiteProvider::quotedValue( dsUri.table() ) )
                                .arg( QgsSpatiaLiteProvider::quotedValue( dsUri.geometryColumn() ) );

tests/src/python/test_provider_postgres.py

@@ -4,6 +4,10 @@
 Note: to prepare the DB, you need to run the sql files specified in
 tests/testdata/provider/testdata_pg.sh
 
+Read tests/README.md about writing/launching tests with PostgreSQL.
+
+Run with ctest -V -R PyQgsPostgresProvider
+
 .. note:: This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation; either version 2 of the License, or
@@ -902,6 +906,7 @@ def testStyle(self):
         status = vl.loadNamedStyle(mFilePath)
         self.assertTrue(status)
 
+        # The style is saved as non-default
         errorMsg = vl.saveStyleToDatabase("by day", "faded greens and elegant patterns", False, "")
         self.assertEqual(errorMsg, "")
 
@@ -933,6 +938,27 @@ def testStyle(self):
         self.assertTrue(res)
         self.assertEqual(errmsg, "")
 
+        # We save now the style again twice but with one as default
+        errorMsg = vl.saveStyleToDatabase("related style", "faded greens and elegant patterns", False, "")
+        self.assertEqual(errorMsg, "")
+        errorMsg = vl.saveStyleToDatabase("default style", "faded greens and elegant patterns", True, "")
+        self.assertEqual(errorMsg, "")
+
+        related_count, idlist, namelist, desclist, errmsg = vl.listStylesInDatabase()
+        self.assertEqual(related_count, 2)
+        self.assertEqual(errmsg, "")
+        self.assertEqual(idlist, ["3", "2"])  # Ids must be reversed.
+        self.assertEqual(namelist, ["default style", "related style"])
+        self.assertEqual(desclist, ["faded greens and elegant patterns"] * 2)
+
+        # We remove these 2 styles
+        res, errmsg = vl.deleteStyleFromDatabase("2")
+        self.assertTrue(res)
+        self.assertEqual(errmsg, "")
+        res, errmsg = vl.deleteStyleFromDatabase("3")
+        self.assertTrue(res)
+        self.assertEqual(errmsg, "")
+
         # table layer_styles does exit, but is now empty
         related_count, idlist, namelist, desclist, errmsg = vl.listStylesInDatabase()
         self.assertEqual(related_count, 0)
@@ -1066,7 +1092,16 @@ def receive(self, msg):
         self.assertTrue(ok)
 
     def testStyleDatabaseWithService(self):
-
+        """Test saving style in DB using a service file.
+
+        To run this test, you first need to create a service with:
+        [qgis_test]
+        host=localhost
+        port=5432
+        dbname=qgis_test
+        user=USERNAME
+        password=PASSWORD
+        """
         myconn = 'service=\'qgis_test\''
         if 'QGIS_PGTEST_DB' in os.environ:
             myconn = os.environ['QGIS_PGTEST_DB']