Fix #1600 UnboundLocalError in RelationChoice deserializer

* Fix UnboundLocalError in RelationChoice deserializer
* changelog
* update tests
* black

news/1600.bugfix

@@ -0,0 +1 @@
+Fix UnboundLocalError in RelationChoice deserializer. @davisagli

src/plone/restapi/deserializer/relationfield.py

@@ -16,6 +16,7 @@
 class RelationChoiceFieldDeserializer(DefaultFieldDeserializer):
     def __call__(self, value):
         obj = None
+        resolved_by = None
 
         if isinstance(value, dict):
             # We are trying to deserialize the output of a serialization
@@ -50,7 +51,10 @@ def __call__(self, value):
 
         if obj is None:
             self.request.response.setStatus(400)
-            raise ValueError(f"Could not resolve object for {resolved_by}={value}")
+            msg = f"Could not resolve object for {value}"
+            if resolved_by:
+                msg += f" (resolved by {resolved_by})"
+            raise ValueError(msg)
 
         self.field.validate(obj)
         return obj

src/plone/restapi/tests/test_dxfield_deserializer.py

@@ -421,7 +421,8 @@ def test_relationchoice_deserialization_from_invalid_intid_raises(self):
         with self.assertRaises(ValueError) as cm:
             self.deserialize("test_relationchoice_field", 123456789)
         self.assertEqual(
-            str(cm.exception), "Could not resolve object for intid=123456789"
+            str(cm.exception),
+            "Could not resolve object for 123456789 (resolved by intid)",
         )
         self.assertEqual(400, self.request.response.getStatus())
 
@@ -433,7 +434,7 @@ def test_relationchoice_deserialization_from_invalid_uid_raises(self):
             )
         self.assertEqual(
             str(cm.exception),
-            "Could not resolve object for UID=ac12b24913cf45c6863937367aacc263",
+            "Could not resolve object for ac12b24913cf45c6863937367aacc263 (resolved by UID)",
         )
         self.assertEqual(400, self.request.response.getStatus())
 
@@ -445,18 +446,25 @@ def test_relationchoice_deserialization_from_invalid_url_raises(self):
             )
         self.assertEqual(
             str(cm.exception),
-            "Could not resolve object for URL=http://nohost/plone/doesnotexist",
+            "Could not resolve object for http://nohost/plone/doesnotexist (resolved by URL)",
         )
         self.assertEqual(400, self.request.response.getStatus())
 
     def test_relationchoice_deserialization_from_invalid_path_raises(self):
         with self.assertRaises(ValueError) as cm:
             self.deserialize("test_relationchoice_field", "/doesnotexist")
         self.assertEqual(
-            str(cm.exception), "Could not resolve object for path=/doesnotexist"
+            str(cm.exception),
+            "Could not resolve object for /doesnotexist (resolved by path)",
         )
         self.assertEqual(400, self.request.response.getStatus())
 
+    def test_relationchoice_deserialization_from_wrong_type_raises(self):
+        with self.assertRaises(ValueError) as cm:
+            self.deserialize("test_relationchoice_field", None)
+        self.assertEqual(str(cm.exception), "Could not resolve object for None")
+        self.assertEqual(400, self.request.response.getStatus())
+
     def test_relationlist_deserialization_returns_list_of_documents(self):
         doc2 = self.portal[
             self.portal.invokeFactory(