[db-manager] Store exception text in the task and pass it over to the caller

Fix #2019 - DBManager fails to display error messages with virtual layers

python/core/auto_generated/qgsvirtuallayertask.sip.in

@@ -58,6 +58,20 @@ Reloads the data.
 
 %Docstring
 Cancels the pending query and the parent task.
+%End
+
+    QString exceptionText() const;
+%Docstring
+Return the exception text or an empty string if no exceptions were raised
+
+.. versionadded:: 3.4
+%End
+
+    void setExceptionText( const QString &exceptionText );
+%Docstring
+Sets the ``exceptionText``
+
+.. versionadded:: 3.4
 %End
 
 };

python/plugins/db_manager/db_plugins/plugin.py

@@ -50,9 +50,6 @@ class BaseError(Exception):
     def __unicode__(self):
         return self.msg
 
-    def __str__(self):
-        return str(self).encode('utf-8')
-
 
 class InvalidDataException(BaseError):
     pass

python/plugins/db_manager/db_plugins/vlayers/data_model.py

@@ -113,6 +113,8 @@ class LSqlResultModelAsync(SqlResultModelAsync):
     def modelDone(self):
         self.status = self.task.status
         self.model = self.task.model
+        if self.task.subtask.exceptionText():
+            self.error = BaseError(self.task.subtask.exceptionText())
         self.done.emit()
 
 

src/core/qgsvirtuallayertask.cpp

@@ -37,6 +37,7 @@ bool QgsVirtualLayerTask::run()
   catch ( std::exception &e )
   {
     QgsDebugMsg( QStringLiteral( "Reload error: %1" ).arg( e.what() ) );
+    setExceptionText( e.what() );
     rc = false;
   }
   return rc;
@@ -62,3 +63,13 @@ void QgsVirtualLayerTask::cancel()
   mLayer->dataProvider()->cancelReload();
   QgsTask::cancel();
 }
+
+QString QgsVirtualLayerTask::exceptionText() const
+{
+  return mExceptionText;
+}
+
+void QgsVirtualLayerTask::setExceptionText( const QString &exceptionText )
+{
+  mExceptionText = exceptionText;
+}

src/core/qgsvirtuallayertask.h

@@ -68,7 +68,20 @@ class CORE_EXPORT QgsVirtualLayerTask : public QgsTask
      */
     void cancel() override;
 
+    /**
+     * Return the exception text or an empty string if no exceptions were raised
+     * \since QGIS 3.4
+     */
+    QString exceptionText() const;
+
+    /**
+     * Sets the \a exceptionText
+     * \since QGIS 3.4
+     */
+    void setExceptionText( const QString &exceptionText );
+
   private:
+    QString mExceptionText;
     QgsVirtualLayerDefinition mDefinition;
     std::unique_ptr<QgsVectorLayer> mLayer;
 };

tests/src/python/test_qgsvirtuallayertask.py

@@ -33,17 +33,18 @@ class TestQgsVirtualLayerTask(unittest.TestCase):
 
     def setUp(self):
         self.testDataDir = unitTestDataPath()
-        self.success = False
-        self.fail = False
+        self._success = False
+        self._fail = False
         self.ids = None
         self.task = None
 
     def onSuccess(self):
-        self.success = True
+        self._success = True
         self.ids = [f.id() for f in self.task.layer().getFeatures()]
 
     def onFail(self):
-        self.fail = True
+        self._fail = True
+        self._exceptionText = self.task.exceptionText()
 
     def test(self):
         l1 = QgsVectorLayer(os.path.join(self.testDataDir, "france_parts.shp"), "françéà", "ogr", QgsVectorLayer.LayerOptions(False))
@@ -61,14 +62,29 @@ class TestQgsVirtualLayerTask(unittest.TestCase):
         self.task.taskTerminated.connect(self.onFail)
 
         QgsApplication.taskManager().addTask(self.task)
-        while not self.success and not self.fail:
+        while not self._success and not self._fail:
             QCoreApplication.processEvents()
 
-        self.assertTrue(self.success)
-        self.assertFalse(self.fail)
+        self.assertTrue(self._success)
+        self.assertFalse(self._fail)
 
         self.assertEqual(len(self.ids), 4)
 
+        # Test exception
+        self._success = False
+        self._fail = False
+        df.setQuery('select *')
+        self.task = QgsVirtualLayerTask(df)
+        self.task.taskCompleted.connect(self.onSuccess)
+        self.task.taskTerminated.connect(self.onFail)
+        QgsApplication.taskManager().addTask(self.task)
+        while not self._success and not self._fail:
+            QCoreApplication.processEvents()
+
+        self.assertFalse(self._success)
+        self.assertTrue(self._fail)
+        self.assertEqual(self._exceptionText, 'Query preparation error on PRAGMA table_info(_tview): no tables specified', self._exceptionText)
+
 
 if __name__ == '__main__':
     unittest.main()