[IMP] base: Warning on m2o required field with ondelete set to 'Set NULL'

Since a required field can not be empty: a warning message will
be thrown if a many2one required field has the "on_delete"
attribute set to "Set NULL".

Task ID 2250533

closes odoo/odoo#50751

X-original-commit: 084555c6395b484a85ec9d386fbc8afc8aec1f8c
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

odoo/addons/base/i18n/base.pot

@@ -22181,6 +22181,12 @@ msgstr ""
 msgid "The list of models that extends the current model."
 msgstr ""
 
+#. module: base
+#: code:addons/base/models/ir_model.py:522
+#, python-format
+msgid "The m2o field %s is required but declares its ondelete policy as being 'set null'. Only 'restrict' and 'cascade' make sense."
+msgstr ""
+
 #. module: base
 #: model:ir.model.fields,help:base.field_ir_filters__action_id
 msgid ""

odoo/addons/base/models/ir_model.py

@@ -679,6 +679,16 @@ class IrModelFields(models.Model):
                     'message': _("The table %r if used for other, possibly incompatible fields.") % self.relation_table,
                 }}
 
+    @api.onchange('required', 'ttype', 'on_delete')
+    def _onchange_required(self):
+        for rec in self:
+            if rec.ttype == 'many2one' and rec.required and rec.on_delete == 'set null':
+                return {'warning': {'title': _("Warning"), 'message': _(
+                    "The m2o field %s is required but declares its ondelete policy "
+                    "as being 'set null'. Only 'restrict' and 'cascade' make sense."
+                    % (rec.name)
+                )}}
+
     def _get(self, model_name, name):
         """ Return the (sudoed) `ir.model.fields` record with the given model and name.
         The result may be an empty recordset if the model is not found.