[UPD] raise user error when deleting a liasse attached to a bdx

models/scop_liasse_fiscale.py

 # © 2021 Le Filament (<http://www.le-filament.com>)
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
 
-from odoo import api, fields, models
+from odoo import _, api, fields, models
+from odoo.exceptions import UserError
 
 
 class ScopLiasseFiscale(models.Model):
@@ -358,6 +359,20 @@ class ScopLiasseFiscale(models.Model):
             liasse._compute_contribution_indus()
             liasse._compute_contribution_idf()
 
+    # ------------------------------------------------------
+    # Override ORM
+    # ------------------------------------------------------
+    def unlink(self):
+        for liasse in self:
+            if self.env["scop.bordereau"].search([("liasse_fiscale_id", "=", liasse.id)]):
+                raise UserError(
+                    _(
+                        "Il n'est pas possible de supprimer cette liasse, elle est liée "
+                        "à un bordereau de cotisation."
+                    )
+                )
+        return super().unlink()
+
     # ------------------------------------------------------
     # Business Function
     # ------------------------------------------------------