Change how users delete entries from the database

Add a button to delete a row from the data table. This deletion can be reverted until the changes are saved to the database. Because we changed the way entries are deleted, a popup now asks user to confirms that they want to save changes to the database.

This merge request only changes the way the user deletes an entry from the database. It does not fix any problem covered by #189 (closed).

Implement part of #196 (closed) because some of the functionalities there is required for this merge request.

sohstationviewer/view/db_config/db_config_dialog.py

@@ -524,12 +524,15 @@ class UiDBInfoDialog(OneWindowAtATimeDialog):
     @QtCore.Slot()
     def delete_table_row(self, row_delete_button: QtWidgets.QPushButton):
         """
-        Remove all data edit widgets from a row and notify the user that they
-        deleted a row from the data table. Also convert the delete button into
-        an undo button.
+        Delete a row from the table.
 
-        On the backend, format a SQL statement to delete the row from the
-        database and queue it to be run when saving changes.
+        If the row contains data that is not in the database (i.e. rows added
+        by the user), remove it completely.
+
+        Otherwise, remove all data edit widgets from a row and notify the user
+        that they deleted the row. Also convert the delete button into an undo
+        button. On the backend, format a SQL statement to delete the row from
+        the database and queue it to be run when saving changes.
 
         :param row_delete_button: the delete button assigned to the row to be
             deleted
@@ -543,8 +546,11 @@ class UiDBInfoDialog(OneWindowAtATimeDialog):
         row_idx = self.data_table_widget.rowAt(delete_button_y)
 
         if row_idx >= len(self.data_list):
-            # If the deleted row is one that the user added, we can simply
-            # delete it.
+            # Deleting a row that is not in the database. Because no rows that
+            # are in the database are removed, and the user can only add rows
+            # at the end of the data table, it suffices to check that the index
+            # of the removed row is greater than the length of the data
+            # retrieved from the database.
             self.remove_row(row_idx)
         else:
             primary_key = self.data_list[row_idx][0]
@@ -559,8 +565,6 @@ class UiDBInfoDialog(OneWindowAtATimeDialog):
                 row_idx, self.total_col - 1, undo_button
             )
 
-            # Format the SQL statement that will delete the chosen row from the
-            # database and queue it for execution.
             delete_sql = (f"DELETE FROM {self.table_name} "
                           f"WHERE {self.col_name}='{primary_key}'")
             delete_sql += self.delete_sql_supplement
@@ -655,7 +659,7 @@ class UiDBInfoDialog(OneWindowAtATimeDialog):
         #             del self.changes_by_rowid[widget_idx]
         #     except KeyError:
         #         pass
-        if self.has_changes() and need_confirmation:
+        if self.has_changes() and not need_confirmation:
             save_prompt = ('Do you want to save the changes you made? This '
                            'action cannot be undone.')
             choice = QMessageBox.question(self, 'Saving changes', save_prompt,