From 857db1f4f4c3e0144ecfb4a6e521791bc6892382 Mon Sep 17 00:00:00 2001
From: Samy Mostafa Shaawat <samy.shaawat@gmail.com>
Date: Sat, 17 Oct 2026 19:26:52 +0300
Subject: [PATCH] [FIX] fs_attachment: serve the thumbnail of an attachment,
 not its parent file

_get_fs_attachment_for_field returned the attachment itself for any field,
including the ones stored in their own attachment like the thumbnail.
---
 fs_attachment/models/ir_binary.py         | 10 +++++--
 fs_attachment/tests/test_fs_attachment.py | 33 +++++++++++++++++++++++
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/fs_attachment/models/ir_binary.py b/fs_attachment/models/ir_binary.py
index b2e187913d..8fd9e0bc17 100644
--- a/fs_attachment/models/ir_binary.py
+++ b/fs_attachment/models/ir_binary.py
@@ -19,9 +19,15 @@ class IrBinary(models.AbstractModel):
     _inherit = "ir.binary"
 
     def _get_fs_attachment_for_field(self, record, field_name):
-        if record._name == "ir.attachment" and record.fs_filename:
-            return record
         field_def = record._fields.get(field_name)
+        # a field stored in its own attachment (ex: thumbnail) is not the file of
+        # the attachment itself
+        if (
+            record._name == "ir.attachment"
+            and record.fs_filename
+            and not (field_def and field_def.attachment)
+        ):
+            return record
         if field_def:
             record._check_field_access(field_def, "read")
             if field_def.attachment and field_def.store:
diff --git a/fs_attachment/tests/test_fs_attachment.py b/fs_attachment/tests/test_fs_attachment.py
index 42dd4cd734..45bd169829 100644
--- a/fs_attachment/tests/test_fs_attachment.py
+++ b/fs_attachment/tests/test_fs_attachment.py
@@ -1,5 +1,6 @@
 # Copyright 2023 ACSONE SA/NV (http://acsone.eu).
 # License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
+import copy
 import os
 from pathlib import Path
 from unittest import mock
@@ -568,3 +569,35 @@ def test_store_in_db_instead_of_object_storage_domain(self):
                 ]
             ),
         )
+
+    def test_get_fs_attachment_for_field_stored_in_attachment(self):
+        """A field stored in its own attachment (ex: the thumbnail added by mail)
+        must not be replaced by the file of the parent attachment"""
+        parent = (
+            self.env["ir.attachment"]
+            .with_context(storage_location=self.temp_backend.code)
+            .create({"name": "doc.pdf", "raw": b"parent"})
+        )
+        thumbnail = (
+            self.env["ir.attachment"]
+            .with_context(storage_location=self.temp_backend.code)
+            .create(
+                {
+                    "name": "thumbnail",
+                    "raw": b"thumbnail",
+                    "res_model": "ir.attachment",
+                    "res_id": parent.id,
+                    "res_field": "thumbnail",
+                }
+            )
+        )
+        field = copy.copy(parent._fields["raw"])
+        field.attachment = True
+        field.store = True
+        ir_binary = self.env["ir.binary"]
+        fields_with_thumbnail = {**parent._fields, "thumbnail": field}
+        with mock.patch.object(type(parent), "_fields", fields_with_thumbnail):
+            self.assertEqual(
+                ir_binary._get_fs_attachment_for_field(parent, "thumbnail"), thumbnail
+            )
+        self.assertEqual(ir_binary._get_fs_attachment_for_field(parent, "raw"), parent)