Should I be using a reactive variable in my list-detail view, and if so where?

[lofidevops]

Below is a simple list-detail layout for a ticket browser, intended as a minimal front-end to GitHub issues, Jira or the like. A wrapper object is used to query the backend. When you pick a list item, the detail pane is reset. This is a familiar pre-AJAX MVC pattern. My intuition is that I "should" rather define a reactive variable, especially if I can make the code less verbose, but I couldn't figure out where. Perhaps the ticket_id? If so, how do I trigger an update to the detail pane when the ticket_id is changed?

# Copyright 2023 David Seaward
# SPDX-License-Identifier: CC0-1.0

SOURCE: SourceWrapper
empty_options = [("", "")]

class TicketBody(VerticalScroll):

    def compose(self):
        global SOURCE

        yield Label("Ticket", id="TicketLabel")
        yield Label("...", id="TicketText")
        yield Label("Sprint", id="SprintLabel")
        yield Select(empty_options, id="SprintSelect")
        yield Label("Epic", id="EpicLabel")
        yield Select(empty_options, id="EpicSelect")
        yield Label("Description", id="DescriptionLabel")
        yield Label("...", id="DescriptionText")

    def reset_values(self, ticket_id):
        global SOURCE
        ticket = SOURCE.get_ticket(ticket_id)

        ticket_text = self.query_one("#TicketText", Label)
        ticket_text.update(ticket.full_title)
        sprint_select = self.query_one("#SprintSelect", Select)
        sprint_select.set_options(SOURCE.get_sprint_select_items())
        sprint_select.value = ticket.sprint_reference
        epic_select = self.query_one("#EpicSelect", Select)
        epic_select.set_options(SOURCE.get_epic_select_items())
        epic_select.value = ticket.epic_reference
        description_text = self.query_one("#DescriptionText", Label)
        description_text.update(ticket.description)


class TicketBrowser(App):
    CSS_PATH = "browser.style"

    def compose(self) -> ComposeResult:
        global SOURCE

        yield OptionList(*SOURCE.get_ticket_option_items(), id="sidebar")
        yield TicketBody(id="body")
        yield Footer()

    @on(OptionList.OptionHighlighted)
    def on_option_list_option_highlighted(self, event: OptionList.OptionHighlighted) -> None:
        if event.option_id is not None:
            body = self.query_one("#body", TicketBody)
            body.reset_values(event.option_id)

[TomJGooding]

My intuition is that I "should" rather define a reactive variable, especially if I can make the code less verbose [...] If so, how do I trigger an update to the detail pane

Textual has watch methods that will be called when when reactive attributes are modified. But you would still need to handle all the updates to your 'detail pane' - so unless I am missing something I don't think adding a reactive attribute would add much benefit here, at least from your example code?

(I would suggest getting rid of all those global variables though!)