account_advanced_protection_features/models/account_move.py

@@ -5,11 +5,12 @@ class AccountMove(models.Model):
     _inherit = 'account.move'
 
     def button_draft(self):
-        if self.is_move_sent and self.journal_id.prevent_reset_to_draft_sent_invoice:
+        for move in self:
+            if move.is_move_sent and move.journal_id.prevent_reset_to_draft_sent_invoice:
                 raise UserError(_(
                     "You cannot reset to draft this invoice because it has been sent by email."
                 ))
-        return super(AccountMove, self).button_draft()
+        return super().button_draft()
 
     @api.ondelete(at_uninstall=False)
     def _check_posted(self):

account_advanced_protection_features/tests/__init__.py

@@ -0,0 +1 @@
+from . import test_account_move

account_advanced_protection_features/tests/test_account_move.py

@@ -0,0 +1,52 @@
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
+
+from odoo.tests.common import TransactionCase
+
+class TestAccountMoveButtonDraft(TransactionCase):
+
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+        cls.partner = cls.env["res.partner"].create({"name": "Test Partner"})
+        cls.journal = cls.env["account.journal"].search(
+            [("type", "=", "sale")], limit=1
+        )
+        cls.account = cls.env["account.account"].search(
+            [("account_type", "=", "income")], limit=1
+        )
+
+    def _create_invoice(self):
+        return self.env["account.move"].create({
+            "move_type": "out_invoice",
+            "partner_id": self.partner.id,
+            "journal_id": self.journal.id,
+            "invoice_line_ids": [
+                (0, 0, {
+                    "name": "Test line",
+                    "quantity": 1,
+                    "price_unit": 100.0,
+                    "account_id": self.account.id,
+                }),
+            ],
+        })
+
+    def test_button_draft_multiple_moves(self):
+        """Test that button_draft works on multiple account.move records.
+        """
+        # Create two invoices
+        invoice1 = self._create_invoice()
+        invoice2 = self._create_invoice()
+
+        # Post both invoices
+        invoice1.action_post()
+        invoice2.action_post()
+
+        # Combine them into a recordset
+        invoices = invoice1 | invoice2
+
+        # This should not raise "Expected singleton" error
+        invoices.button_draft()
+
+        # Verify both are back to draft
+        self.assertEqual(invoice1.state, "draft")
+        self.assertEqual(invoice2.state, "draft")