fix: Fix JSON deserialization, schema inference, and silent fallback …

…for nested collection types - Add nested list handling in proto_json from_json_object (list of lists was raising ParseError since no branch matched list-typed elements) - Fix pa_to_feast_value_type to recognize nested list PyArrow types (list<item: list<item: T>>) instead of crashing with KeyError - Replace silent String fallback in _str_to_feast_type with ValueError to surface corrupted tag values instead of silently losing type info - Strengthen test coverage: type str roundtrip, inner value verification, multi-value batch, proto JSON roundtrip, PyArrow nested type inference Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com> Signed-off-by: soojin <soojin@dable.io>
feast-dev · franciscojavierarceo · Apr 2, 2026 · Mar 17, 2026 · Mar 18, 2026 · Mar 18, 2026
commit e57ddd23d0670bd8d72eb107a0343662a54d506f
@@ -272,9 +272,10 @@ def _str_to_feast_type(type_str: str) -> FeastType:
     try:
         return PrimitiveFeastType[type_str]
     except KeyError:
-        from feast.types import String
-
-        return String
+        raise ValueError(
+            f"Unknown FeastType: {type_str!r}. "
+            f"Valid primitive types: {[t.name for t in PrimitiveFeastType]}"
+        )
 
 
 def _serialize_struct_schema(struct_type: Struct) -> str:

@@ -92,6 +92,15 @@ def from_json_object(
             if len(value) == 0:
                 # Clear will mark the struct as modified so it will be created even if there are no values
                 message.int64_list_val.Clear()
+            elif isinstance(value[0], list):
+                # Nested collection (list of lists).
+                # Default to list_list_val since JSON transport loses the
+                # outer/inner set distinction.
+                rv = RepeatedValue()
+                for inner in value:
+                    inner_val = rv.val.add()
+                    from_json_object(parser, inner, inner_val)
+                message.list_list_val.CopyFrom(rv)
             elif isinstance(value[0], bool):
                 message.bool_list_val.val.extend(value)
             elif isinstance(value[0], str):

@@ -1258,7 +1258,11 @@ def pa_to_feast_value_type(pa_type_as_str: str) -> ValueType:
     is_list = False
     if pa_type_as_str.startswith("list<item: "):
         is_list = True
-        pa_type_as_str = pa_type_as_str.replace("list<item: ", "").replace(">", "")
+        inner_str = pa_type_as_str[len("list<item: ") : -1]
+        # Check for nested list (list of lists) before stripping
+        if inner_str.startswith("list<item: "):
+            return ValueType.LIST_LIST
+        pa_type_as_str = inner_str
 
     if pa_type_as_str.startswith("timestamp"):
         value_type = ValueType.UNIX_TIMESTAMP

@@ -103,6 +103,33 @@ def test_feature_list(proto_json_patch):
     )
 
 
+def test_nested_collection_json_roundtrip(proto_json_patch):
+    """Nested collection values (list of lists) should survive JSON roundtrip."""
+    from feast.protos.feast.types.Value_pb2 import Value
+
+    # Build a Value with list_list_val containing [[1,2],[3,4,5]]
+    value_proto = Value()
+    inner1 = value_proto.list_list_val.val.add()
+    inner1.int64_list_val.val.extend([1, 2])
+    inner2 = value_proto.list_list_val.val.add()
+    inner2.int64_list_val.val.extend([3, 4, 5])
+
+    # Serialize to JSON
+    value_json = MessageToDict(value_proto)
+    assert isinstance(value_json, list)
+    assert len(value_json) == 2
+    assert value_json[0] == [1, 2]
+    assert value_json[1] == [3, 4, 5]
+
+    # Deserialize back from JSON
+    feature_vector_str = '{"values": [[[1, 2], [3, 4, 5]]]}'
+    feature_vector_proto = FeatureVector()
+    Parse(feature_vector_str, feature_vector_proto)
+    assert len(feature_vector_proto.values) == 1
+    assert feature_vector_proto.values[0].WhichOneof("val") == "list_list_val"
+    assert len(feature_vector_proto.values[0].list_list_val.val) == 2
+
+
 @pytest.fixture(scope="module")
 def proto_json_patch():
     proto_json.patch()
@@ -1664,10 +1664,54 @@ def test_set_list_no_dedup_inner(self):
         assert result[0] == [1, 1, 2]
         assert result[1] == [3, 3]
 
-    def test_feast_value_type_to_pa_nested(self):
-        """Test feast_value_type_to_pa for nested collection types."""
-        pa_type = feast_value_type_to_pa(ValueType.LIST_LIST)
-        assert pa_type == pyarrow.list_(pyarrow.list_(pyarrow.string()))
+    def test_list_list_proto_roundtrip_values(self):
+        """Test that LIST_LIST roundtrip preserves actual inner values."""
+        values = [[[1, 2, 3], [4, 5]]]
+        protos = python_values_to_proto_values(values, ValueType.LIST_LIST)
+        result = feast_value_type_to_python_type(protos[0])
+        assert result[0] == [1, 2, 3]
+        assert result[1] == [4, 5]
+
+    def test_set_list_proto_roundtrip_values(self):
+        """Test that SET_LIST roundtrip preserves actual inner values."""
+        values = [[["a", "b"], ["c"]]]
+        protos = python_values_to_proto_values(values, ValueType.SET_LIST)
+        result = feast_value_type_to_python_type(protos[0])
+        assert result[0] == ["a", "b"]
+        assert result[1] == ["c"]
+
+    def test_multi_value_batch_nested(self):
+        """Test multiple nested collection values in a single batch."""
+        values = [[[1, 2], [3]], [[4], [5, 6]]]
+        protos = python_values_to_proto_values(values, ValueType.LIST_LIST)
+        assert len(protos) == 2
+        r0 = feast_value_type_to_python_type(protos[0])
+        r1 = feast_value_type_to_python_type(protos[1])
+        assert r0 == [[1, 2], [3]]
+        assert r1 == [[4], [5, 6]]
 
-        pa_type = feast_value_type_to_pa(ValueType.SET_SET)
-        assert pa_type == pyarrow.list_(pyarrow.list_(pyarrow.string()))
+    def test_feast_value_type_to_pa_nested(self):
+        """Test feast_value_type_to_pa for all nested collection types."""
+        for vt in (
+            ValueType.LIST_LIST,
+            ValueType.LIST_SET,
+            ValueType.SET_LIST,
+            ValueType.SET_SET,
+        ):
+            pa_type = feast_value_type_to_pa(vt)
+            assert pa_type == pyarrow.list_(pyarrow.list_(pyarrow.string()))
+
+    def test_pa_to_feast_value_type_nested(self):
+        """Test pa_to_feast_value_type recognizes nested list PyArrow types."""
+        assert (
+            pa_to_feast_value_type("list<item: list<item: int64>>")
+            == ValueType.LIST_LIST
+        )
+        assert (
+            pa_to_feast_value_type("list<item: list<item: string>>")
+            == ValueType.LIST_LIST
+        )
+        assert (
+            pa_to_feast_value_type("list<item: list<item: double>>")
+            == ValueType.LIST_LIST
+        )
@@ -134,7 +134,7 @@ def test_nested_field_roundtrip():
     """Field with nested collection type should survive to_proto -> from_proto."""
     test_cases = [
         ("aa", Array(Array(String))),
-        ("as", Array(Set(Int32))),
+        ("as_field", Array(Set(Int32))),
         ("sa", Set(Array(Float64))),
         ("ss", Set(Set(Bool))),
     ]
@@ -146,6 +146,10 @@ def test_nested_field_roundtrip():
         assert restored.dtype.to_value_type() == dtype.to_value_type(), (
             f"dtype mismatch for {name}: {restored.dtype} vs {dtype}"
         )
+        # Verify inner type is preserved (not just ValueType equality)
+        assert str(restored.dtype) == str(dtype), (
+            f"Inner type lost for {name}: got {restored.dtype}, expected {dtype}"
+        )
         assert restored.tags == {"user_tag": "value"}, (
             f"Tags should not contain internal tags for {name}"
         )
@@ -178,6 +182,40 @@ def test_uuid_set_feast_type():
     assert from_value_type(set_time_uuid.to_value_type()) == set_time_uuid
 
 
+def test_feast_type_str_roundtrip():
+    """_feast_type_to_str and _str_to_feast_type should roundtrip for nested types."""
+    from feast.field import _feast_type_to_str, _str_to_feast_type
+
+    test_cases = [
+        Array(Array(String)),
+        Array(Array(Int32)),
+        Array(Array(Float64)),
+        Array(Set(Int64)),
+        Array(Set(Bool)),
+        Set(Array(String)),
+        Set(Array(Float32)),
+        Set(Set(Int32)),
+        Set(Set(Float64)),
+    ]
+    for dtype in test_cases:
+        s = _feast_type_to_str(dtype)
+        restored = _str_to_feast_type(s)
+        assert str(restored) == str(dtype), (
+            f"Roundtrip failed: {dtype} -> '{s}' -> {restored}"
+        )
+
+
+def test_str_to_feast_type_invalid():
+    """_str_to_feast_type should raise ValueError on unrecognized type names."""
+    from feast.field import _str_to_feast_type
+
+    with pytest.raises(ValueError, match="Unknown FeastType"):
+        _str_to_feast_type("INVALID_TYPE")
+
+    with pytest.raises(ValueError, match="Unknown FeastType"):
+        _str_to_feast_type("Strig")
+
+
 def test_all_value_types():
     for value in ValueType:
         # We do not support the NULL type.