diff --git a/addons/kosbar_erp_ext/__manifest__.py b/addons/kosbar_erp_ext/__manifest__.py
index b9b1672..3369167 100644
--- a/addons/kosbar_erp_ext/__manifest__.py
+++ b/addons/kosbar_erp_ext/__manifest__.py
@@ -9,6 +9,7 @@
         'security/ir.model.access.csv',
         'data/ir_sequence.xml',
         'data/stock_picking_type.xml',
+        'views/product_views.xml',
     ],
     'installable': True,
     'application': False,
diff --git a/addons/kosbar_erp_ext/models/__init__.py b/addons/kosbar_erp_ext/models/__init__.py
index 91e7030..eac5bc4 100644
--- a/addons/kosbar_erp_ext/models/__init__.py
+++ b/addons/kosbar_erp_ext/models/__init__.py
@@ -2,3 +2,4 @@ from . import sale_order
 from . import stock_picking
 from . import product_category
 from . import product_template
+from . import product_product
diff --git a/addons/kosbar_erp_ext/models/product_product.py b/addons/kosbar_erp_ext/models/product_product.py
new file mode 100644
index 0000000..40b11e9
--- /dev/null
+++ b/addons/kosbar_erp_ext/models/product_product.py
@@ -0,0 +1,13 @@
+from odoo import models, fields, api
+
+
+class ProductProduct(models.Model):
+    _inherit = 'product.product'
+
+    item_code = fields.Char(
+        string='Item Code',
+        related='product_tmpl_id.item_code',
+        store=True,
+        readonly=True,
+        help='Item Code dari template produk (variant menampilkan kode template).',
+    )
diff --git a/addons/kosbar_erp_ext/models/product_template.py b/addons/kosbar_erp_ext/models/product_template.py
index 40e51d3..4595b44 100644
--- a/addons/kosbar_erp_ext/models/product_template.py
+++ b/addons/kosbar_erp_ext/models/product_template.py
@@ -9,10 +9,24 @@ class ProductTemplate(models.Model):
 
     item_code = fields.Char(
         string='Item Code',
-        index=True,
-        help='Kombinasi: parent_kode + kategori_kode + id_produk(4digit) + nama_produk_tanpa_spasi(lower)',
+        store=True,
+        readonly=False,  # biar view bisa pakai; kita atur readonly di XML
+        help='Kombinasi: parent_kode + kategori_kode + id(+4 digit) + nama_tanpa_spasi(lower). '
+             'Read-only, dipakai sbg stock keeping unit code.',
     )
 
+    @api.onchange('categ_id')
+    def _onchange_categ_preview(self):
+        """Saat create belum simpan id -> tampilkan pratinjau gabungan kode kategori."""
+        if self.categ_id and not self.env.context.get('default_product_tmpl_id') \
+                and not self.id and not self.item_code:
+            cat = self.categ_id
+            if cat and not cat.code:
+                cat.code = f'{cat.id:02d}'
+            parent = cat.parent_id.code if cat.parent_id else ''
+            own = cat.code or ''
+            self.item_code = f'{parent}{own}'
+
     @api.constrains('item_code')
     def _check_item_code_unique(self):
         for rec in self:
@@ -25,32 +39,35 @@ class ProductTemplate(models.Model):
                     f'({dup.name}). Item Code harus unik.'
                 )
 
-    def _generate_item_code(self):
-        """Generate item_code: parent_code + cat_code + id:04d + name_slug"""
-        for p in self:
-            cat = p.categ_id
-            parent_code = ''
-            cat_code = '00'
+    def _category_prefix(self, cat):
+        """Return gabungan kode kategori (parent+own), 4 digit atau 00."""
+        if not cat:
+            return '00'
+        if not cat.code:
+            cat.code = f'{cat.id:02d}'
+        parent_code = cat.parent_id.code if cat.parent_id else ''
+        own_code = cat.code or ''
+        return f'{parent_code}{own_code}'
 
-            if cat:
-                # Pastikan kategori punya code (calculate jika belum ada)
-                if not cat.code:
-                    cat.code = f'{cat.id:02d}'
-                parent_code = cat.parent_id.code if cat.parent_id else ''
-                cat_code = cat.code
+    def _name_slug(self, name):
+        return re.sub(r'\s+', '', (name or '').lower())
 
-            # slug: lowercase, remove semua spasi
-            name_slug = re.sub(r'\s+', '', (p.name or '').lower())
-            p.item_code = f'{parent_code}{cat_code}{p.id:04d}{name_slug}'
+    def _full_item_code(self, obj):
+        """Compute full item_code: prefix kategori + id:04d + name_slug."""
+        prefix = self._category_prefix(obj.categ_id)
+        oid = obj.id or 0
+        return f'{prefix}{oid:04d}{self._name_slug(obj.name)}'
 
     @api.model_create_multi
     def create(self, vals_list):
         records = super().create(vals_list)
-        records._generate_item_code()
+        for r in records:
+            r.item_code = r._full_item_code(r)
         return records
 
     def write(self, vals):
         res = super().write(vals)
         if 'name' in vals or 'categ_id' in vals:
-            self._generate_item_code()
-        return res
\ No newline at end of file
+            for r in self:
+                r.item_code = r._full_item_code(r)
+        return res
diff --git a/addons/kosbar_erp_ext/references/custom-product-code.md b/addons/kosbar_erp_ext/references/custom-product-code.md
new file mode 100644
index 0000000..defb87c
--- /dev/null
+++ b/addons/kosbar_erp_ext/references/custom-product-code.md
@@ -0,0 +1,118 @@
+# Custom Product Code & Item Code Automation
+
+## Overview
+Odoo 17/19 Community tidak punya field `code` standar untuk product category. Untuk kebutuhan stock keeping unit (SKU) yang unik, kita buat field `item_code` yang di‑generate otomatis dari:
+
+```
+item_code = parent_category_code (2 digit) + category_code (2 digit) + product_id (4 digit) + name_slug (lowercase, no space)
+```
+
+Contoh:
+- Kategori anak: id=06, parent=01 → prefix = `0106`
+- Produk: id=3, nama="Backup BRT 30 x 36 x 1,25 mm"
+- Hasil: `01060003backupbrt30x36x1,25mm`
+
+## Implementation Steps
+
+### 1. Extend `product.category` → field `code`
+```python
+class ProductCategory(models.Model):
+    _inherit = 'product.category'
+    code = fields.Char(string='Category Code', compute='_compute_code', store=True, size=4)
+
+    @api.model_create_multi
+    def create(self, vals_list):
+        records = super().create(vals_list)
+        for r in records:
+            r.code = f'{r.id:02d}'
+        return records
+```
+
+### 2. Extend `product.template` → field `item_code`
+Field `item_code`:
+- **Stored** (`store=True`) — dipakai untuk pencarian & unique index.
+- **Read‑only di view** — tidak boleh ditulis manual.
+- **On‑change preview** → tampilkan prefix kategori saat buat produk baru.
+
+```python
+class ProductTemplate(models.Model):
+    _inherit = 'product.template'
+
+    item_code = fields.Char(string='Item Code', store=True, readonly=False)
+
+    _sql_constraints = [
+        ('item_code_unique', 'UNIQUE(item_code)', 'Item Code harus unik.'),
+    ]
+
+    @api.model_create_multi
+    def create(self, vals_list):
+        records = super().create(vals_list)
+        for r in records:
+            r.item_code = r._full_item_code(r)
+        return records
+
+    def write(self, vals):
+        res = super().write(vals)
+        if 'name' in vals or 'categ_id' in vals:
+            for r in self:
+                r.item_code = r._full_item_code(r)
+        return res
+```
+
+### 3. Extend `product.product` (varian)
+Untuk produk ber‑varian, `item_code` diturunkan via related field ke template:
+
+```python
+class ProductProduct(models.Model):
+    _inherit = 'product.product'
+
+    item_code = fields.Char(
+        string='Item Code',
+        related='product_tmpl_id.item_code',
+        store=True,
+        readonly=True,
+    )
+```
+
+### 4. XML View — field read‑only
+```xml
+<!-- product_template_form_view inheritance -->
+<field name="default_code" position="after">
+    <field name="item_code" readonly="1" placeholder="Terisi otomatis"/>
+</field>
+```
+
+### 5. PostgreSQL — Unique Index (optional, backup)
+Constraint `__sql_constraints` sudah menambah unique index via Odoo ORM. Untuk kecepatan lebih cepat di PostgreSQL level, dapat manual:
+
+```sql
+CREATE UNIQUE INDEX IF NOT EXISTS product_template_item_code_uniq
+ON product_template (item_code) WHERE item_code IS NOT NULL;
+```
+
+### 6. Migration — isi data existing
+```python
+env.cr.execute("""
+    CREATE UNIQUE INDEX IF NOT EXISTS product_template_item_code_uniq
+    ON product_template (item_code) WHERE item_code IS NOT NULL
+""")
+
+cats = env['product.category'].search([])
+for c in cats:
+    if not c.code:
+        c.code = f'{c.id:02d}'
+
+prods = env['product.template'].search([])
+for p in prods:
+    p.item_code = p._full_item_code(p)
+```
+
+## Pitfalls
+- `@api.depends('id')` **not allowed** di Odoo 19. Namun `id` tersedia di `create()` setelah super() selesai.
+- Field `code` di kategori **harus `size` ditentukan** ( Odoo 17+ lint error tanpa `size`)
+- Product dengan `categ_id = False` → gunakan fallback `00`.
+- **Item Code read‑only di view**: bila pakai `store=True`, field tetap dapat ditulis via ORM (API). Untuk mencegah manual edit, gunakan `readonly=True` + `@api.constrains` untuk validasi.
+
+## References
+- `models/product_template.py` — contoh implementasi lengkap (sudah ada di addon `kosbar_erp_ext`)
+- `views/product_views.xml` — XML view inheritance
\ No newline at end of file
diff --git a/addons/kosbar_erp_ext/views/product_views.xml b/addons/kosbar_erp_ext/views/product_views.xml
new file mode 100644
index 0000000..effd975
--- /dev/null
+++ b/addons/kosbar_erp_ext/views/product_views.xml
@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="utf-8"?>
+<odoo>
+    <!-- Product Template form: tampilkan Item Code read_only -->
+    <record id="view_product_template_item_code" model="ir.ui.view">
+        <field name="name">product.template.form.item.code</field>
+        <field name="model">product.template</field>
+        <field name="inherit_id" ref="product.product_template_form_view"/>
+        <field name="arch" type="xml">
+            <field name="default_code" position="after">
+                <field name="item_code" readonly="1"
+                       placeholder="Terisi otomatis dari kategori &amp; nama"/>
+            </field>
+        </field>
+    </record>
+
+    <!-- Product Variant form (product.product): Item Code read_only -->
+    <record id="view_product_product_item_code" model="ir.ui.view">
+        <field name="name">product.product.form.item.code</field>
+        <field name="model">product.product</field>
+        <field name="inherit_id" ref="product.product_variant_easy_edit_view"/>
+        <field name="arch" type="xml">
+            <field name="default_code" position="after">
+                <field name="item_code" readonly="1"/>
+            </field>
+        </field>
+    </record>
+</odoo>