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

@@ -506,37 +506,42 @@ class UiDBInfoDialog(OneWindowAtATimeDialog):
         self.data_table_widget.setCellWidget(row_idx, self.total_col - 1,
                                              delete_button)
         delete_button.clicked.connect(
-            lambda: self.delete_data_row(delete_button)
+            lambda: self.delete_table_row(delete_button)
         )
 
     @QtCore.Slot()
-    def delete_data_row(self, row_delete_button: QtWidgets.QPushButton):
+    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.
 
         On the backend, format a SQL statement to delete the row from the
-        database and store it for use when saving changes.
+        database and queue it to be run when saving changes.
 
         :param row_delete_button: the delete button assigned to the row to be
             deleted
         """
+        # If we don't have this line, there is an issue with the undo button
+        # flickering in behind the 0 row label before moving to the correct
+        # location.
+        self.data_table_widget.setUpdatesEnabled(False)
+
         delete_button_y = row_delete_button.y()
-        chosen_row = self.data_table_widget.rowAt(delete_button_y)
+        row_idx = self.data_table_widget.rowAt(delete_button_y)
 
         # We want to tell user what they removed. However, we will be removing
         # all the data edit widgets before displaying the delete notification
         # to user, so we have to save the needed information beforehand.
-        primary_key = self.data_table_widget.cellWidget(chosen_row, 1).text()
+        primary_key = self.data_table_widget.cellWidget(row_idx, 1).text()
 
         # Remove all the data edit widgets in the chosen row.
         data_edit_widgets_count = self.total_col - 2
         for i in range(1, data_edit_widgets_count + 1):
-            self.data_table_widget.removeCellWidget(chosen_row, i)
-        self.data_table_widget.setSpan(chosen_row, 1,
-                                       1, data_edit_widgets_count)
+            self.data_table_widget.removeCellWidget(row_idx, i)
 
+        self.data_table_widget.setSpan(row_idx, 1,
+                                       1, data_edit_widgets_count)
         # Show the notification that the row has been deleted.
         row_deleted_notifications = (
             f'{self.column_headers[1]} '
@@ -546,15 +551,43 @@ class UiDBInfoDialog(OneWindowAtATimeDialog):
         row_deleted_label = QtWidgets.QLabel(row_deleted_notifications)
         row_deleted_label.setTextFormat(QtCore.Qt.RichText)
         row_deleted_label.setAlignment(QtCore.Qt.AlignCenter)
-        self.data_table_widget.setCellWidget(chosen_row, 1,
+        self.data_table_widget.setCellWidget(row_idx, 1,
                                              row_deleted_label)
+        undo_button = QtWidgets.QPushButton('Undo')
+        undo_button.clicked.connect(
+            lambda: self.undo_delete_table_row(row_idx)
+        )
+        self.data_table_widget.setCellWidget(
+            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
-        self.queued_row_delete_sqls[chosen_row] = delete_sql
+        self.queued_row_delete_sqls[row_idx] = delete_sql
+
+        self.data_table_widget.setUpdatesEnabled(True)
+
+    def undo_delete_table_row(self, row_idx: int):
+        """
+        Undo the deletion of a table row and dequeue the corresponding SQL
+        statement from the list of SQL statements to be run when saving.
+
+        :param row_idx: the row number of the row being deleted
+        """
+        # If we don't have this line, there is an issue with the undo button
+        # flickering in behind the 0 row label before moving to the correct
+        # location.
+        self.data_table_widget.setUpdatesEnabled(False)
+
+        self.data_table_widget.removeCellWidget(row_idx, 1)
+        self.data_table_widget.setSpan(row_idx, 1, 1, 1)
+        self.set_row_widgets(row_idx)
+        del self.queued_row_delete_sqls[row_idx]
+
+        self.data_table_widget.setUpdatesEnabled(True)
 
     def data_type_changed(self):
         """