VIEW_ACTION_PATTERNS(3)      RSX Manual      VIEW_ACTION_PATTERNS(3)

NAME
    view_action_patterns - Best practices for SPA view actions with
    dynamic content loading

SYNOPSIS
    Recommended pattern for view/detail pages that load a single record:

    Action Class (Feature_View_Action.js):
        @route('/feature/view/:id')
        @layout('Frontend_Spa_Layout')
        @spa('Frontend_Spa_Controller::index')
        @title('Feature Details')
        class Feature_View_Action extends Spa_Action {
            on_create() {
                this.data.record = { name: '' };
                this.data.error_data = null;
                this.data.loading = true;
            }

            async on_load() {
                try {
                    this.data.record = await Controller.get({
                        id: this.args.id
                    });
                } catch (e) {
                    this.data.error_data = e;
                }
                this.data.loading = false;
            }
        }

    Template (Feature_View_Action.jqhtml):
        <Define:Feature_View_Action>
            <Page>
                <% if (this.data.loading) { %>
                    <Loading_Spinner $message="Loading..." />
                <% } else if (this.data.error_data) { %>
                    <Universal_Error_Page_Component
                        $error_data="<%= this.data.error_data %>"
                        $record_type="Feature"
                        $back_label="Go back to Features"
                        $back_url="<%= Rsx.Route('Feature_Index_Action') %>"
                    />
                <% } else { %>
                    <!-- Normal content here -->
                <% } %>
            </Page>
        </Define:Feature_View_Action>

DESCRIPTION
    This document describes the recommended pattern for building view/detail
    pages in RSpade SPA applications. The pattern provides:

    - Loading state with spinner during data fetch
    - Automatic error handling for all Ajax error types
    - Clean three-state template (loading → error → content)
    - Consistent user experience across all view pages

    This is an opinionated best practice from the RSpade starter template.
    Developers are free to implement alternatives, but this pattern handles
    common cases well and provides a consistent structure.

THE THREE-STATE PATTERN
    Every view action has exactly three possible states:

    1. LOADING - Data is being fetched
       - Show Loading_Spinner component
       - Prevents flash of empty/broken content
       - User knows something is happening

    2. ERROR - Data fetch failed
       - Show Universal_Error_Page_Component
       - Automatically routes to appropriate error display
       - Handles not found, unauthorized, server errors, etc.

    3. SUCCESS - Data loaded successfully
       - Show normal page content
       - Safe to access this.data.record properties

    Template structure:
        <% if (this.data.loading) { %>
            <!-- State 1: Loading -->
        <% } else if (this.data.error_data) { %>
            <!-- State 2: Error -->
        <% } else { %>
            <!-- State 3: Success -->
        <% } %>

ACTION CLASS STRUCTURE
    on_create() - Initialize defaults
        on_create() {
            // Stub object prevents undefined errors during first render
            this.data.record = { name: '' };

            // Error holder - null means no error
            this.data.error_data = null;

            // Start in loading state
            this.data.loading = true;
        }

        Key points:
        - Initialize this.data.record with empty stub matching expected shape
        - Prevents "cannot read property of undefined" during initial render
        - Set loading=true so spinner shows immediately

    async on_load() - Fetch data with error handling
        async on_load() {
            try {
                this.data.record = await Controller.get({
                    id: this.args.id
                });
            } catch (e) {
                this.data.error_data = e;
            }
            this.data.loading = false;
        }

        Key points:
        - Wrap Ajax call in try/catch
        - Store caught error in this.data.error_data (not re-throw)
        - Always set loading=false in finally or after try/catch
        - Error object has .code, .message, .metadata from Ajax system

UNIVERSAL ERROR COMPONENT
    The Universal_Error_Page_Component automatically displays the right
    error UI based on error.code:

    Required arguments:
        $error_data   - The error object from catch block
        $record_type  - Human name: "Project", "Contact", "User"
        $back_label   - Button text: "Go back to Projects"
        $back_url     - Where back button navigates

    Error types handled:
        Ajax.ERROR_NOT_FOUND      → "Project Not Found" with back button
        Ajax.ERROR_UNAUTHORIZED   → "Access Denied" message
        Ajax.ERROR_AUTH_REQUIRED  → "Login Required" with login button
        Ajax.ERROR_SERVER         → "Server Error" with retry button
        Ajax.ERROR_NETWORK        → "Connection Error" with retry button
        Ajax.ERROR_VALIDATION     → Field error list
        Ajax.ERROR_GENERIC        → Generic error with retry

HANDLING SPECIFIC ERRORS DIFFERENTLY
    Sometimes you need custom handling for specific error types while
    letting others go to the universal handler:

        async on_load() {
            try {
                this.data.record = await Controller.get({id: this.args.id});
            } catch (e) {
                if (e.code === Ajax.ERROR_NOT_FOUND) {
                    // Custom handling: redirect to create page
                    Spa.dispatch(Rsx.Route('Feature_Create_Action'));
                    return;
                }
                // All other errors: use universal handler
                this.data.error_data = e;
            }
            this.data.loading = false;
        }

    Or in the template for different error displays:

        <% } else if (this.data.error_data) { %>
            <% if (this.data.error_data.code === Ajax.ERROR_NOT_FOUND) { %>
                <!-- Custom not-found UI -->
                <div class="text-center">
                    <p>This project doesn't exist yet.</p>
                    <a href="..." class="btn btn-primary">Create It</a>
                </div>
            <% } else { %>
                <!-- Standard error handling -->
                <Universal_Error_Page_Component ... />
            <% } %>
        <% } else { %>

LOADING SPINNER
    The Loading_Spinner component provides consistent loading UI:

        <Loading_Spinner />
        <Loading_Spinner $message="Loading project details..." />

    Located at: rsx/theme/components/feedback/loading_spinner.jqhtml

COMPLETE EXAMPLE
    From rsx/app/frontend/projects/Projects_View_Action.js:

        @route('/projects/view/:id')
        @layout('Frontend_Spa_Layout')
        @spa('Frontend_Spa_Controller::index')
        @title('Project Details')
        class Projects_View_Action extends Spa_Action {
            on_create() {
                this.data.project = { name: '' };
                this.data.error_data = null;
                this.data.loading = true;
            }

            async on_load() {
                try {
                    this.data.project = await Frontend_Projects_Controller
                        .get_project({ id: this.args.id });
                } catch (e) {
                    this.data.error_data = e;
                }
                this.data.loading = false;
            }
        }

    The template uses the three-state pattern with full page content
    in the success state. See the actual file for complete template.

WHEN TO USE THIS PATTERN
    Use for:
    - Detail/view pages loading a single record by ID
    - Edit pages that need to load existing data
    - Any page where initial data might not exist or be accessible

    Not needed for:
    - List pages (DataGrid handles its own loading/error states)
    - Create pages (no existing data to load)
    - Static pages without dynamic data

SEE ALSO
    spa(3), ajax_error_handling(3), jqhtml(3)

RSX Framework                    2025-11-21           VIEW_ACTION_PATTERNS(3)