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/channel_dialog.py

@@ -2,6 +2,7 @@
 channel_dialog.py
 GUI to add/edit/remove channels
 """
+from PySide2.QtWidgets import QMessageBox
 
 from sohstationviewer.view.db_config.db_config_dialog import UiDBInfoDialog
 from sohstationviewer.database.process_db import execute_db
@@ -23,6 +24,7 @@ class ChannelDialog(UiDBInfoDialog):
             'channel', 'channels', resize_content_columns=[0, 4, 5, 6],
             need_data_type_choice=True, required_columns={3: 'Param'},
             check_fk=False)
+        self.delete_sql_supplement = f" AND dataType='{self.data_type}'"
         self.setWindowTitle("Edit/Add/Delete Channels")
 
     def update_data_table_widget_items(self):
@@ -46,9 +48,9 @@ class ChannelDialog(UiDBInfoDialog):
         self.data_table_widget.cellWidget(0, 5).setText('')
         self.data_table_widget.cellWidget(0, 6).setValue(0)
 
-    def add_row(self, row_idx, fk=False):
+    def set_row_widgets(self, row_idx, fk=False):
         """
-        Add a row of widgets to self.data_table_widgets.
+        Set the widgets in a row in self.data_table_widgets.
 
         :param row_idx: index of row to add
         :param fk: bool: True if there is a foreign constrain that prevents the
@@ -63,14 +65,51 @@ class ChannelDialog(UiDBInfoDialog):
         self.add_widget(self.data_list, row_idx, 5)  # unit
         self.add_widget(self.data_list, row_idx, 6,
                         range_values=[0, 5])  # fixPoint
+        self.add_delete_button_to_row(row_idx, fk)
 
     def data_type_changed(self):
         """
-        Load new self.data_list when self.data_type_combo_box's value is
-            changed
-        """
-        self.data_type = self.data_type_combo_box.currentText()
-        self.update_data_table_widget_items()
+        Method called when the data type of the data table is changed.
+
+        If there are unsaved changes, ask the user what to do. If the user
+        proceeds with the change, load channels of the new data type from the
+        database and populate the data table with these new channels. The user
+        can choose to save or not save the changes to the database with this
+        option. Otherwise, change the data type back and do nothing.
+        """
+        # If the user cancel changing the data type when there are unsaved
+        # changes, the data type is changed back, which causes another
+        # execution of this method and thus, the prompt dialog shows up
+        # twice. This if statement fixes that problem.
+        if self.data_type == self.data_type_combo_box.currentText():
+            return
+
+        if not self.has_changes():
+            self.data_type = self.data_type_combo_box.currentText()
+            self.update_data_table_widget_items()
+            self.delete_sql_supplement = f" AND dataType='{self.data_type}'"
+            return
+
+        unsaved_changes_prompt = (
+            '<h3>Unsaved Changes</h3>'
+            'Are you sure you want to change the data type? '
+            'Any changes you made will not be saved?'
+        )
+        options = QMessageBox.Save | QMessageBox.Discard | QMessageBox.Cancel
+        user_choice = QMessageBox.warning(self, 'Unsaved Changes',
+                                          unsaved_changes_prompt, options)
+        if user_choice != QMessageBox.Cancel:
+            if user_choice == QMessageBox.Save:
+                self.save_changes(need_confirmation=False)
+            elif user_choice == QMessageBox.Discard:
+                self.undo_all_deletes()
+            self.data_type = self.data_type_combo_box.currentText()
+            self.update_data_table_widget_items()
+            self.delete_sql_supplement = f" AND dataType='{self.data_type}'"
+        else:
+            # Cover both the case where the cancel button is pressed and the
+            # case where the exit button is pressed.
+            self.data_type_combo_box.setCurrentText(self.data_type)
 
     def get_data_list(self):
         """