INTPYTHON-599 Make a field's custom transforms available in embedded model queries

Author: timgraham

django_mongodb_backend/fields/embedded_model.py

@@ -163,26 +163,23 @@ def get_transform(self, name):
         Validate that `name` is either a field of an embedded model or a
         lookup on an embedded model's field.
         """
-        result = None
         if isinstance(self.ref_field, EmbeddedModelField):
             opts = self.ref_field.embedded_model._meta
             new_field = opts.get_field(name)
-            result = KeyTransformFactory(name, new_field)
+            return KeyTransformFactory(name, new_field)
+        if transform := self.ref_field.get_transform(name):
+            return transform
+        suggested_lookups = difflib.get_close_matches(name, self.ref_field.get_lookups())
+        if suggested_lookups:
+            suggested_lookups = " or ".join(suggested_lookups)
+            suggestion = f", perhaps you meant {suggested_lookups}?"
         else:
-            if self.ref_field.get_transform(name) is None:
-                suggested_lookups = difflib.get_close_matches(name, self.ref_field.get_lookups())
-                if suggested_lookups:
-                    suggested_lookups = " or ".join(suggested_lookups)
-                    suggestion = f", perhaps you meant {suggested_lookups}?"
-                else:
-                    suggestion = "."
-                raise FieldDoesNotExist(
-                    f"Unsupported lookup '{name}' for "
-                    f"{self.ref_field.__class__.__name__} '{self.ref_field.name}'"
-                    f"{suggestion}"
-                )
-            result = KeyTransformFactory(name, self.ref_field)
-        return result
+            suggestion = "."
+        raise FieldDoesNotExist(
+            f"Unsupported lookup '{name}' for "
+            f"{self.ref_field.__class__.__name__} '{self.ref_field.name}'"
+            f"{suggestion}"
+        )
 
     def preprocess_lhs(self, compiler, connection):
         previous = self

docs/source/releases/5.1.x.rst

@@ -7,8 +7,9 @@ Django MongoDB Backend 5.1.x
 
 *Unreleased*
 
-- Added support for a field's custom lookups in ``EmbeddedModelField``, e.g.
-  ``ArrayField``’s ``contains``, ``contained__by``, etc.
+- Added support for a field's custom lookups and transforms in
+  ``EmbeddedModelField``, e.g. ``ArrayField``’s ``contains``,
+  ``contained__by``, ``len``, etc.
 
 .. _django-mongodb-backend-5.1.0-beta-2:
 

docs/source/releases/5.2.x.rst

@@ -15,5 +15,6 @@ Regarding new features in Django 5.2,
 
 Bug fixes:
 
-- Added support for a field's custom lookups in ``EmbeddedModelField``, e.g.
-  ``ArrayField``’s ``contains``, ``contained__by``, etc.
+- Added support for a field's custom lookups and transforms in
+  ``EmbeddedModelField``, e.g. ``ArrayField``’s ``contains``,
+  ``contained__by``, ``len``, etc.

tests/model_fields_/test_embedded_model.py

@@ -228,6 +228,13 @@ def test_contained_by(self):
             [self.book],
         )
 
+    def test_len(self):
+        self.assertCountEqual(Book.objects.filter(author__skills__len=1), [])
+        self.assertCountEqual(Book.objects.filter(author__skills__len=2), [self.book])
+        # Nested
+        self.assertCountEqual(Book.objects.filter(author__address__tags__len=1), [])
+        self.assertCountEqual(Book.objects.filter(author__address__tags__len=2), [self.book])
+
 
 class InvalidLookupTests(SimpleTestCase):
     def test_invalid_field(self):