@@ -6,8 +6,8 @@ This module demonstrates how to use **native extra fields** (custom fields) in P
 
 It focuses on:
 
-- Registering extra fields on multiple entities (Product, Category, Customer)
-- Covering multiple **scopes** (`common`, `lang`, `shop`) and **types** (bool, date, money, html, json, url, …)
+- Registering extra fields on multiple entities (Product, Category, Customer, Address, CMS, Cart, Order, Combination)
+- Covering multiple **scopes** (`common`, `lang`, `shop`) and **types** (bool, date, money, html, json, url, choice, …)
 - Unregistering extra fields on uninstall (including dropping the SQL storage columns)
 - Rendering the stored values on the Front Office using hooks
 - Making Back Office translation strings visible in the translation interface
@@ -19,6 +19,8 @@ It focuses on:
 - `is_dangerous` (scope: `common`, type: bool)
 - `video_link` (scope: `lang`, type: string/url)
 - `custom_date` (scope: `shop`, type: date)
+- `date_last_seen` (scope: `common`, type: date — written by a FO hook, no form)
+- `packaging_type` (scope: `common`, type: choice)
 
 ### Category (`category`)
 
@@ -29,7 +31,47 @@ It focuses on:
 ### Customer (`customer`)
 
 - `credit_limit` (scope: `common`, type: float / money)
-- `extra_json` (scope: `common`, type: json)
+- `extra_json` (scope: `common`, type: json) — the JSON showcase: the module **writes a PHP
+  structure** (the core encodes it for storage) and **reads back the decoded structure**
+  (iterated in the my-account template)
+- `internal_note` (scope: `common`, type: string, `displayFront: false` — never reaches the FO)
+
+### Address (`address`)
+
+- `delivery_note` (scope: `common`, type: string — grid placement on the manufacturer addresses grid)
+
+### CMS (`cms`) — manual form integration (no `associatedForms`)
+
+- `promo_banner` (scope: `lang`, type: string)
+- `revision_code` (scope: `common`, type: string)
+
+### Cart (`cart`) — a COMMON-only entity
+
+- `delivery_note` (scope: `common`, type: string) — seeded by `actionCartSave`, displayed on the
+  checkout summary (`displayCheckoutSummaryTop`), and **copied onto the order** at validation
+  (`actionValidateOrder`): the cart dies at the end of checkout, so cart values that must
+  survive the purchase have to be copied to the order by the module.
+- The cart has no `cart_lang` / `cart_shop` base table (its `id_lang`/`id_shop` are plain
+  columns), so `lang` and `shop` scopes are rejected at registration for this entity.
+
+### Order (`order`)
+
+- `delivery_note` (scope: `common`, type: string) — filled from the cart at order validation,
+  displayed on the customer's order detail page (`displayOrderDetail`). Registered with the
+  natural entity name `order`: the core resolves the physical table (`orders`) and primary
+  key (`id_order`) from the ObjectModel. No order-grid placement on purpose: the order grid
+  uses id-first pagination, which the generic grid integration cannot join yet (core issue
+  [#42536](https://github.com/PrestaShop/PrestaShop/issues/42536)).
+
+### Combination (`combination`)
+
+- `ean_verified` (scope: `common`, type: bool) — exposed on the Admin API combinations list
+  (`/products/{productId}/combinations`)
+- `restock_note` (scope: `shop`, type: string) — one value per store
+
+Registered with the natural entity name `combination` (the `Combination`,
+`product_attribute` and `ProductAttribute` spellings work identically): the core resolves
+the physical table (`product_attribute`) and primary key (`id_product_attribute`).
 
 ## How to test
 
@@ -81,9 +123,28 @@ This module impacts both Back Office and Front Office.
 
 - My account page: `displayCustomerAccountTop`
 
+### Cart & Order
+
+- Add any product to the cart: `actionCartSave` seeds the cart `delivery_note` (once).
+- Open the cart / checkout: the note is displayed above the cart summary
+  (`displayCheckoutSummaryTop`, read from `{$cart.extra_properties.demoextrafield.delivery_note}`).
+- Place the order: `actionValidateOrder` copies the note onto the order.
+- In the customer account, open the order detail page: the copied note is displayed
+  (`displayOrderDetail`).
+
+### Combination
+
+- Edit a product's combinations: `ean_verified` / `restock_note` are stored per combination
+  (`restock_note` per store).
+- Admin API: `GET /products/{productId}/combinations` returns `extra_demoextrafield_ean_verified`
+  inline on each item.
+
 ### Where to find values in FO templates
 
-On the Front Office, the module displays **only the values stored for this module**, under `extraProperties['demoextrafield']`.
+On the Front Office, the module displays **only the values stored for this module**, under the
+`extra_properties['demoextrafield']` key (snake_case — Smarty/presenter surfaces always use
+`extra_properties`; the camelCase `extraProperties` spelling exists only in the Admin API JSON).
+JSON-typed fields come back as **decoded structures** (arrays), not raw JSON strings.
 
 ## Translation note (Back Office)
 
 
@@ -503,6 +503,120 @@ enumValues: ['standard', 'gift', 'bulk'],
             return false;
         }
 
+        /**
+         * CART extra field — the cart is a COMMON-only entity: it has no cart_lang /
+         * cart_shop base table (its id_lang / id_shop are plain columns), so LANG and
+         * SHOP scopes are rejected at registration. No form/grid/API placements exist
+         * for the cart either; the value is written by a hook and displayed on checkout.
+         */
+
+        // Cart (common) : delivery_note
+        $cartDeliveryNoteRegistered = $this->registerExtraProperty(
+            new ExtraPropertyDefinition(
+                entityName: 'cart',
+                propertyName: 'delivery_note',
+                type: ExtraPropertyType::STRING,
+                scope: ExtraPropertyScope::COMMON,
+                nullable: true,
+                displayFront: true,
+                formType: TextareaType::class,
+                labelWording: 'Delivery note',
+                labelDomain: self::TRANSLATION_DOMAIN,
+                descriptionWording: 'Delivery instructions attached to the cart during checkout',
+                descriptionDomain: self::TRANSLATION_DOMAIN,
+            )
+        );
+        if (!$cartDeliveryNoteRegistered) {
+            $this->_errors[] = $this->trans('Failed to register Cart extra field "delivery_note" (scope: common).', [], 'Modules.Demoextrafield.Admin');
+
+            return false;
+        }
+
+        /**
+         * ORDER extra field — registered with the natural entity name 'order': the core
+         * resolves the physical table ('orders') and the primary key ('id_order') from
+         * the Order ObjectModel. COMMON is the only supported scope (no orders_lang /
+         * orders_shop tables). Deliberately NO order-grid placement: the order grid uses
+         * id-first pagination, which the generic grid integration cannot join yet (core
+         * issue #42536) — the column would render empty.
+         */
+
+        // Order (common) : delivery_note — filled from the cart's note at order validation.
+        $orderDeliveryNoteRegistered = $this->registerExtraProperty(
+            new ExtraPropertyDefinition(
+                entityName: 'order',
+                propertyName: 'delivery_note',
+                type: ExtraPropertyType::STRING,
+                scope: ExtraPropertyScope::COMMON,
+                nullable: true,
+                displayFront: true,
+                formType: TextareaType::class,
+                labelWording: 'Delivery note (copied from the cart)',
+                labelDomain: self::TRANSLATION_DOMAIN,
+                descriptionWording: 'Delivery instructions copied from the cart when the order is validated',
+                descriptionDomain: self::TRANSLATION_DOMAIN,
+            )
+        );
+        if (!$orderDeliveryNoteRegistered) {
+            $this->_errors[] = $this->trans('Failed to register Order extra field "delivery_note" (scope: common).', [], 'Modules.Demoextrafield.Admin');
+
+            return false;
+        }
+
+        /**
+         * COMBINATION extra fields — registered with the natural entity name
+         * 'combination' (the 'Combination'/'product_attribute'/'ProductAttribute'
+         * spellings work identically): the core resolves the physical table
+         * ('product_attribute') and the primary key ('id_product_attribute'). All three
+         * scopes are available (product_attribute_lang / product_attribute_shop exist).
+         */
+
+        // Combination (common) : ean_verified — exposed on the combinations API list.
+        $combinationEanVerifiedRegistered = $this->registerExtraProperty(
+            new ExtraPropertyDefinition(
+                entityName: 'combination',
+                propertyName: 'ean_verified',
+                type: ExtraPropertyType::BOOL,
+                scope: ExtraPropertyScope::COMMON,
+                defaultValue: false,
+                nullable: false,
+                displayFront: true,
+                associatedApis: ['/products/{productId}/combinations'],
+                formType: SwitchType::class,
+                labelWording: 'EAN verified',
+                labelDomain: self::TRANSLATION_DOMAIN,
+                descriptionWording: 'Whether the combination EAN has been verified by the merchant',
+                descriptionDomain: self::TRANSLATION_DOMAIN,
+            )
+        );
+        if (!$combinationEanVerifiedRegistered) {
+            $this->_errors[] = $this->trans('Failed to register Combination extra field "ean_verified" (scope: common).', [], 'Modules.Demoextrafield.Admin');
+
+            return false;
+        }
+
+        // Combination (shop) : restock_note — one value per store.
+        $combinationRestockNoteRegistered = $this->registerExtraProperty(
+            new ExtraPropertyDefinition(
+                entityName: 'combination',
+                propertyName: 'restock_note',
+                type: ExtraPropertyType::STRING,
+                scope: ExtraPropertyScope::SHOP,
+                nullable: true,
+                displayFront: false,
+                formType: TextareaType::class,
+                labelWording: 'Restock note (per store)',
+                labelDomain: self::TRANSLATION_DOMAIN,
+                descriptionWording: 'Internal restocking note, stored per store',
+                descriptionDomain: self::TRANSLATION_DOMAIN,
+            )
+        );
+        if (!$combinationRestockNoteRegistered) {
+            $this->_errors[] = $this->trans('Failed to register Combination extra field "restock_note" (scope: shop).', [], 'Modules.Demoextrafield.Admin');
+
+            return false;
+        }
+
         $hooksRegistered = $this->registerHook('displayProductAdditionalInfo')
             && $this->registerHook('displayCartExtraProductInfo')
             && $this->registerHook('displayHeaderCategory')
@@ -512,7 +626,11 @@ enumValues: ['standard', 'gift', 'bulk'],
             && $this->registerHook('actionCmsPageFormDataProviderData')
             && $this->registerHook('actionAfterCreateCmsPageFormHandler')
             && $this->registerHook('actionAfterUpdateCmsPageFormHandler')
-            && $this->registerHook('displayCMSDisputeInformation');
+            && $this->registerHook('displayCMSDisputeInformation')
+            && $this->registerHook('displayCheckoutSummaryTop')
+            && $this->registerHook('actionCartSave')
+            && $this->registerHook('actionValidateOrder')
+            && $this->registerHook('displayOrderDetail');
         if (!$hooksRegistered) {
             $this->_errors[] = $this->trans('Failed to register one or more hooks.', [], 'Modules.Demoextrafield.Admin');
 
@@ -554,6 +672,11 @@ public function uninstall(): bool
             && $this->unregisterExtraProperty(new ExtraPropertyDefinition('cms', 'promo_banner'), $dropColumn)
             && $this->unregisterExtraProperty(new ExtraPropertyDefinition('cms', 'revision_code'), $dropColumn)
 
+            && $this->unregisterExtraProperty(new ExtraPropertyDefinition('cart', 'delivery_note'), $dropColumn)
+            && $this->unregisterExtraProperty(new ExtraPropertyDefinition('order', 'delivery_note'), $dropColumn)
+            && $this->unregisterExtraProperty(new ExtraPropertyDefinition('combination', 'ean_verified'), $dropColumn)
+            && $this->unregisterExtraProperty(new ExtraPropertyDefinition('combination', 'restock_note'), $dropColumn)
+
             && $this->unregisterHook('displayProductAdditionalInfo')
             && $this->unregisterHook('displayCartExtraProductInfo')
             && $this->unregisterHook('displayHeaderCategory')
@@ -564,6 +687,10 @@ public function uninstall(): bool
             && $this->unregisterHook('actionAfterCreateCmsPageFormHandler')
             && $this->unregisterHook('actionAfterUpdateCmsPageFormHandler')
             && $this->unregisterHook('displayCMSDisputeInformation')
+            && $this->unregisterHook('displayCheckoutSummaryTop')
+            && $this->unregisterHook('actionCartSave')
+            && $this->unregisterHook('actionValidateOrder')
+            && $this->unregisterHook('displayOrderDetail')
 
             && parent::uninstall();
     }
@@ -674,6 +801,99 @@ public function hookDisplayHeaderCategory(): string
         return $this->display(__FILE__, 'views/templates/hook/category_header.tpl');
     }
 
+    /**
+     * Action hook — fires on every cart save.
+     *
+     * Demo of the CART extra field write path: seeds the delivery_note the first time the
+     * cart is persisted (a real module would set it from a checkout form field). Writing
+     * through $cart->update() re-triggers actionCartSave, hence the re-entrancy guard.
+     */
+    public function hookActionCartSave(): void
+    {
+        static $seeding = false;
+        if ($seeding) {
+            return;
+        }
+
+        $cart = $this->context->cart;
+        if (!Validate::isLoadedObject($cart)) {
+            return;
+        }
+
+        $existingNote = $cart->extra_properties['demoextrafield']['delivery_note'];
+        if (is_string($existingNote) && '' !== $existingNote) {
+            return;
+        }
+
+        $seeding = true;
+        try {
+            $cart->extra_properties['demoextrafield']['delivery_note'] = sprintf(
+                'Leave the parcel at the pickup point (demo note seeded on %s).',
+                date('Y-m-d H:i')
+            );
+            $cart->update();
+        } finally {
+            $seeding = false;
+        }
+    }
+
+    /**
+     * Front Office hook (checkout / cart summary).
+     *
+     * Displays the cart delivery_note read through the presented cart: `$cart` is a Smarty
+     * global on every FO page (a CartLazyArray), and the extra properties are exposed under
+     * its `extra_properties` key — snake_case, like every Smarty surface (the camelCase
+     * `extraProperties` spelling belongs to the Admin API JSON only).
+     */
+    public function hookDisplayCheckoutSummaryTop(array $params): string
+    {
+        return $this->display(__FILE__, 'views/templates/hook/checkout_summary_top.tpl');
+    }
+
+    /**
+     * Action hook — fires when an order is validated.
+     *
+     * The cart dies at the end of checkout (its cookie is dropped once the order exists),
+     * so a cart-level value that must stay visible after the purchase has to be copied
+     * onto the order. This is the intended pattern: the module owns the copy.
+     *
+     * Also a live demo of the entity-name resolution: the definition was registered as
+     * 'order' while the ObjectModel writes through its physical table 'orders' /
+     * primary key 'id_order'.
+     */
+    public function hookActionValidateOrder(array $params): void
+    {
+        $cart = $params['cart'] ?? null;
+        $order = $params['order'] ?? null;
+        if (!$cart instanceof Cart || !$order instanceof Order || (int) $order->id <= 0) {
+            return;
+        }
+
+        $deliveryNote = $cart->extra_properties['demoextrafield']['delivery_note'];
+        if (!is_string($deliveryNote) || '' === $deliveryNote) {
+            return;
+        }
+
+        $order->extra_properties['demoextrafield']['delivery_note'] = $deliveryNote;
+        $order->update();
+    }
+
+    /**
+     * Front Office hook (order detail page, customer account).
+     * Displays the order's extra fields (e.g. the delivery_note copied from the cart).
+     */
+    public function hookDisplayOrderDetail(array $params): string
+    {
+        $order = $params['order'] ?? null;
+        if (!$order instanceof Order || (int) $order->id <= 0) {
+            return '';
+        }
+
+        $this->context->smarty->assign('orderObjectModel', $order);
+
+        return $this->display(__FILE__, 'views/templates/hook/order_detail.tpl');
+    }
+
     /**
      * Front Office hook (customer my-account page).
      *
@@ -697,6 +917,18 @@ public function hookDisplayCustomerAccountTop(): string
             return '';
         }
 
+        // JSON showcase: write a real PHP structure — the writer json_encodes it for
+        // storage, the constraint (Assert\Json) validates the encoded string, and reads
+        // give the decoded structure back (iterable in the template below).
+        $extraJson = $customer->extra_properties['demoextrafield']['extra_json'];
+        if (empty($extraJson)) {
+            $customer->extra_properties['demoextrafield']['extra_json'] = [
+                'loyalty' => ['points' => 0, 'tier' => 'bronze'],
+                'preferences' => ['newsletter' => true],
+            ];
+            $customer->update();
+        }
+
         $this->context->smarty->assign('customerObjectModel', $customer);
 
         return $this->display(__FILE__, 'views/templates/hook/customer_account_top.tpl');