Fix import of shapefiles to postgres - regression introduced in 5abdfcb (#3652)

(cherry picked from commit a965a13)

Author: wonder-sk

src/providers/postgres/qgspostgresprovider.cpp

@@ -3526,6 +3526,9 @@ QgsVectorLayerImport::ImportError QgsPostgresProvider::createEmptyLayer( const Q
         fldIdx = -1; // it is incremented in the for loop, i.e. restarts at 0
       }
     }
+
+    pkList = QStringList( primaryKey );
+    pkType = QStringList( "serial" );
   }
   else
   {

tests/src/python/test_provider_postgres.py

@@ -471,17 +471,27 @@ def testImportKey(self):
 
         def testKey(lyr, key, kfnames):
             self.execSQLCommand('DROP TABLE IF EXISTS qgis_test.import_test')
-            uri = '%s table="qgis_test"."import_test" (g) key=\'%s\'' % (self.dbconn, key)
+            uri = '%s table="qgis_test"."import_test" (g)' % self.dbconn
+            if key is not None:
+                uri += ' key=\'%s\'' % key
             err = QgsVectorLayerImport.importLayer(lyr, uri, "postgres", lyr.crs())
             self.assertEqual(err[0], QgsVectorLayerImport.NoError,
                              'unexpected import error {0}'.format(err))
             olyr = QgsVectorLayer(uri, "y", "postgres")
             self.assertTrue(olyr.isValid())
             flds = lyr.fields()
             oflds = olyr.fields()
-            self.assertEquals(oflds.size(), flds.size())
-            for i in range(0, oflds.size()):
-                self.assertEqual(oflds[i].name(), flds[i].name())
+            if key is None:
+                # if the pkey was not given, it will create a pkey
+                self.assertEquals(oflds.size(), flds.size() + 1)
+                self.assertEquals(oflds[0].name(), kfnames[0])
+                for i in range(flds.size()):
+                    self.assertEqual(oflds[i + 1].name(), flds[i].name())
+            else:
+                # pkey was given, no extra field generated
+                self.assertEquals(oflds.size(), flds.size())
+                for i in range(oflds.size()):
+                    self.assertEqual(oflds[i].name(), flds[i].name())
             pks = olyr.pkAttributeList()
             self.assertEquals(len(pks), len(kfnames))
             for i in range(0, len(kfnames)):
@@ -491,6 +501,7 @@ def testKey(lyr, key, kfnames):
         testKey(lyr, '"f1"', ['f1'])
         testKey(lyr, '"f1","F2"', ['f1', 'F2'])
         testKey(lyr, '"f1","F2","f3"', ['f1', 'F2', 'f3'])
+        testKey(lyr, None, ['id'])
 
 
 class TestPyQgsPostgresProviderCompoundKey(unittest.TestCase, ProviderTestCase):