[ADD] user friendly error handling for restricted qty on ecommerce app

sale_restricted_qty_website_sale/models/__init__.py

@@ -0,0 +1,2 @@
+from . import product_restricted_qty_mixin
+from . import sale_order_line

sale_restricted_qty_website_sale/models/product_restricted_qty_mixin.py

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+# Copyright 2026 Élabore (https://elabore.coop)
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
+
+from odoo import _, models
+from odoo.tools import float_is_zero
+from odoo.tools.misc import formatLang
+
+
+class ProductRestrictedQtyMixin(models.AbstractModel):
+    """Extending the OCA abstract mixin makes these helpers available at once
+    on product.product, product.template and product.category."""
+
+    _inherit = "product.restricted.qty.mixin"
+
+    def _format_restricted_qty(self, qty):
+        """Short form: 6 rather than 6.0, and a locale-aware separator
+        for decimals."""
+        if float_is_zero(qty - int(qty), precision_digits=3):
+            return str(int(qty))
+        return formatLang(self.env, qty)
+
+    def _get_restricted_qty_hint(self):
+        """Sentence shown to the customer. Empty when nothing restricts him.
+
+        OCA semantics: `force_sale_min_qty` / `force_sale_max_qty` set to Yes
+        make the bound purely indicative -- the constraint does not block, so
+        we announce nothing rather than promising a rule that does not exist.
+        """
+        self.ensure_one()
+        uom = self.uom_id.name if "uom_id" in self._fields else ""
+        parts = []
+        if self.sale_min_qty and not self.force_sale_min_qty:
+            parts.append(
+                _(
+                    "minimum order: %(qty)s %(uom)s",
+                    qty=self._format_restricted_qty(self.sale_min_qty),
+                    uom=uom,
+                )
+            )
+        if self.sale_multiple_qty:
+            parts.append(
+                _(
+                    "in multiples of %(qty)s %(uom)s",
+                    qty=self._format_restricted_qty(self.sale_multiple_qty),
+                    uom=uom,
+                )
+            )
+        if self.sale_max_qty and not self.force_sale_max_qty:
+            parts.append(
+                _(
+                    "maximum: %(qty)s %(uom)s",
+                    qty=self._format_restricted_qty(self.sale_max_qty),
+                    uom=uom,
+                )
+            )
+        if not parts:
+            return ""
+        hint = " · ".join(parts)
+        return hint[0].upper() + hint[1:]

sale_restricted_qty_website_sale/models/sale_order_line.py

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+from odoo import _, api, models
+from odoo.exceptions import ValidationError
+
+
+class SaleOrderLine(models.Model):
+    _inherit = "sale.order.line"
+
+    @api.constrains(
+        "product_uom_qty", "sale_min_qty", "sale_max_qty", "sale_multiple_qty"
+    )
+    def check_constraint_restricted_qty(self):
+        """Rewrite the error message raised by `sale_restricted_qty`.
+
+        The upstream message is written for a salesperson: it dumps the
+        offending products and explains how to tick "force min quantity" on
+        the product form. Unreadable for an eCommerce customer.
+
+        Detection is left to the OCA module -- the `is_qty_*` fields stay the
+        single source of truth. Only the wording is replaced, so an upstream
+        change to the rules is followed without breaking anything.
+        """
+        try:
+            return super().check_constraint_restricted_qty()
+        except ValidationError:
+            raise ValidationError(self._get_restricted_qty_error_message()) from None
+
+    def _get_restricted_qty_error_message(self):
+        """Customer-facing message, one line per unmet restriction."""
+        details = []
+        for line in self:
+            product = line.product_id
+            if not product.force_sale_min_qty and line.is_qty_less_min_qty:
+                details.append(
+                    _(
+                        "%(product)s: minimum order quantity is %(qty)s.",
+                        product=product.display_name,
+                        qty=product._format_restricted_qty(line.sale_min_qty),
+                    )
+                )
+            if not product.force_sale_max_qty and line.is_qty_bigger_max_qty:
+                details.append(
+                    _(
+                        "%(product)s: maximum order quantity is %(qty)s.",
+                        product=product.display_name,
+                        qty=product._format_restricted_qty(line.sale_max_qty),
+                    )
+                )
+            if line.is_qty_not_multiple_qty:
+                details.append(
+                    _(
+                        "%(product)s: must be ordered in multiples of %(qty)s.",
+                        product=product.display_name,
+                        qty=product._format_restricted_qty(line.sale_multiple_qty),
+                    )
+                )
+
+        return _(
+            "The selected quantity is not available for sale:\n\n"
+            "%s\n\n"
+            "Please adjust the quantity.",
+            "\n".join(details),
+        )