fix(extra_fields): Fix issue with substream partition router picking extra fields

airbyte_cdk/sources/declarative/partition_routers/cartesian_product_stream_slicer.py

@@ -149,6 +149,7 @@ def stream_slices(self) -> Iterable[StreamSlice]:
         for stream_slice_tuple in product:
             partition = dict(ChainMap(*[s.partition for s in stream_slice_tuple]))  # type: ignore # ChainMap expects a MutableMapping[Never, Never] for reasons
             cursor_slices = [s.cursor_slice for s in stream_slice_tuple if s.cursor_slice]
+            extra_fields = dict(ChainMap(*[s.extra_fields for s in stream_slice_tuple]))  # type: ignore # ChainMap expects a MutableMapping[Never, Never] for reasons
             if len(cursor_slices) > 1:
                 raise ValueError(
                     f"There should only be a single cursor slice. Found {cursor_slices}"
@@ -157,7 +158,9 @@ def stream_slices(self) -> Iterable[StreamSlice]:
                 cursor_slice = cursor_slices[0]
             else:
                 cursor_slice = {}
-            yield StreamSlice(partition=partition, cursor_slice=cursor_slice)
+            yield StreamSlice(
+                partition=partition, cursor_slice=cursor_slice, extra_fields=extra_fields
+            )
 
     def set_initial_state(self, stream_state: StreamState) -> None:
         """

unit_tests/sources/declarative/partition_routers/helpers.py

@@ -0,0 +1,93 @@
+#
+# Copyright (c) 2025 Airbyte, Inc., all rights reserved.
+#
+
+from typing import Any, Iterable, List, Mapping, Optional, Union
+
+from airbyte_cdk.models import SyncMode
+from airbyte_cdk.sources.declarative.declarative_stream import DeclarativeStream
+from airbyte_cdk.sources.declarative.interpolation import InterpolatedString
+from airbyte_cdk.sources.streams.checkpoint import Cursor
+from airbyte_cdk.sources.types import Record, StreamSlice
+
+
+class MockStream(DeclarativeStream):
+    def __init__(self, slices, records, name, cursor_field="", cursor=None):
+        self.config = {}
+        self._slices = slices
+        self._records = records
+        self._stream_cursor_field = (
+            InterpolatedString.create(cursor_field, parameters={})
+            if isinstance(cursor_field, str)
+            else cursor_field
+        )
+        self._name = name
+        self._state = {"states": []}
+        self._cursor = cursor
+
+    @property
+    def name(self) -> str:
+        return self._name
+
+    @property
+    def primary_key(self) -> Optional[Union[str, List[str], List[List[str]]]]:
+        return "id"
+
+    @property
+    def state(self) -> Mapping[str, Any]:
+        return self._state
+
+    @state.setter
+    def state(self, value: Mapping[str, Any]) -> None:
+        self._state = value
+
+    @property
+    def is_resumable(self) -> bool:
+        return bool(self._cursor)
+
+    def get_cursor(self) -> Optional[Cursor]:
+        return self._cursor
+
+    def stream_slices(
+        self,
+        *,
+        sync_mode: SyncMode,
+        cursor_field: List[str] = None,
+        stream_state: Mapping[str, Any] = None,
+    ) -> Iterable[Optional[StreamSlice]]:
+        for s in self._slices:
+            if isinstance(s, StreamSlice):
+                yield s
+            else:
+                yield StreamSlice(partition=s, cursor_slice={})
+
+    def read_records(
+        self,
+        sync_mode: SyncMode,
+        cursor_field: List[str] = None,
+        stream_slice: Mapping[str, Any] = None,
+        stream_state: Mapping[str, Any] = None,
+    ) -> Iterable[Mapping[str, Any]]:
+        # The parent stream's records should always be read as full refresh
+        assert sync_mode == SyncMode.full_refresh
+
+        if not stream_slice:
+            result = self._records
+        else:
+            result = [
+                Record(data=r, associated_slice=stream_slice, stream_name=self.name)
+                for r in self._records
+                if r["slice"] == stream_slice["slice"]
+            ]
+
+        yield from result
+
+        # Update the state only after reading the full slice
+        cursor_field = self._stream_cursor_field.eval(config=self.config)
+        if stream_slice and cursor_field and result:
+            self._state["states"].append(
+                {cursor_field: result[-1][cursor_field], "partition": stream_slice["slice"]}
+            )
+
+    def get_json_schema(self) -> Mapping[str, Any]:
+        return {}

unit_tests/sources/declarative/partition_routers/test_cartesian_product_partition_router.py

@@ -11,11 +11,16 @@
     CartesianProductStreamSlicer,
     ListPartitionRouter,
 )
+from airbyte_cdk.sources.declarative.partition_routers.substream_partition_router import (
+    ParentStreamConfig,
+    SubstreamPartitionRouter,
+)
 from airbyte_cdk.sources.declarative.requesters.request_option import (
     RequestOption,
     RequestOptionType,
 )
 from airbyte_cdk.sources.types import StreamSlice
+from unit_tests.sources.declarative.partition_routers.helpers import MockStream
 
 
 @pytest.mark.parametrize(
@@ -171,6 +176,68 @@ def test_substream_slicer(test_name, stream_slicers, expected_slices):
     assert slices == expected_slices
 
 
+@pytest.mark.parametrize(
+    "test_name, stream_slicers, expected_slices",
+    [
+        (
+            "test_single_stream_slicer",
+            [
+                SubstreamPartitionRouter(
+                    parent_stream_configs=[
+                        ParentStreamConfig(
+                            stream=MockStream(
+                                [{}],
+                                [
+                                    {"a": {"b": 0}, "extra_field_key": "extra_field_value_0"},
+                                    {"a": {"b": 1}, "extra_field_key": "extra_field_value_1"},
+                                    {"a": {"c": 2}, "extra_field_key": "extra_field_value_2"},
+                                    {"a": {"b": 3}, "extra_field_key": "extra_field_value_3"},
+                                ],
+                                "first_stream",
+                            ),
+                            parent_key="a/b",
+                            partition_field="first_stream_id",
+                            parameters={},
+                            config={},
+                            extra_fields=[["extra_field_key"]],
+                        )
+                    ],
+                    parameters={},
+                    config={},
+                ),
+            ],
+            [
+                StreamSlice(
+                    partition={"first_stream_id": 0, "parent_slice": {}},
+                    cursor_slice={},
+                    extra_fields={"extra_field_key": "extra_field_value_0"},
+                ),
+                StreamSlice(
+                    partition={"first_stream_id": 1, "parent_slice": {}},
+                    cursor_slice={},
+                    extra_fields={"extra_field_key": "extra_field_value_1"},
+                ),
+                StreamSlice(
+                    partition={"first_stream_id": 3, "parent_slice": {}},
+                    cursor_slice={},
+                    extra_fields={"extra_field_key": "extra_field_value_3"},
+                ),
+            ],
+        )
+    ],
+)
+def test_substream_slicer_with_extra_fields(test_name, stream_slicers, expected_slices):
+    slicer = CartesianProductStreamSlicer(stream_slicers=stream_slicers, parameters={})
+    slices = [s for s in slicer.stream_slices()]
+    partitions = [s.partition for s in slices]
+    expected_partitions = [s.partition for s in expected_slices]
+    assert partitions == expected_partitions
+
+    extra_fields = [s.extra_fields for s in slices]
+    expected_extra_fields = [s.extra_fields for s in expected_slices]
+    assert extra_fields == expected_extra_fields
+
+
 def test_stream_slices_raises_exception_if_multiple_cursor_slice_components():
     stream_slicers = [
         DatetimeBasedCursor(

unit_tests/sources/declarative/partition_routers/test_substream_partition_router.py

@@ -34,6 +34,7 @@
 from airbyte_cdk.sources.streams.checkpoint import Cursor
 from airbyte_cdk.sources.types import Record, StreamSlice
 from airbyte_cdk.utils import AirbyteTracedException
+from unit_tests.sources.declarative.partition_routers.helpers import MockStream
 
 parent_records = [{"id": 1, "data": "data1"}, {"id": 2, "data": "data2"}]
 more_records = [
@@ -63,88 +64,6 @@
 )
 
 
-class MockStream(DeclarativeStream):
-    def __init__(self, slices, records, name, cursor_field="", cursor=None):
-        self.config = {}
-        self._slices = slices
-        self._records = records
-        self._stream_cursor_field = (
-            InterpolatedString.create(cursor_field, parameters={})
-            if isinstance(cursor_field, str)
-            else cursor_field
-        )
-        self._name = name
-        self._state = {"states": []}
-        self._cursor = cursor
-
-    @property
-    def name(self) -> str:
-        return self._name
-
-    @property
-    def primary_key(self) -> Optional[Union[str, List[str], List[List[str]]]]:
-        return "id"
-
-    @property
-    def state(self) -> Mapping[str, Any]:
-        return self._state
-
-    @state.setter
-    def state(self, value: Mapping[str, Any]) -> None:
-        self._state = value
-
-    @property
-    def is_resumable(self) -> bool:
-        return bool(self._cursor)
-
-    def get_cursor(self) -> Optional[Cursor]:
-        return self._cursor
-
-    def stream_slices(
-        self,
-        *,
-        sync_mode: SyncMode,
-        cursor_field: List[str] = None,
-        stream_state: Mapping[str, Any] = None,
-    ) -> Iterable[Optional[StreamSlice]]:
-        for s in self._slices:
-            if isinstance(s, StreamSlice):
-                yield s
-            else:
-                yield StreamSlice(partition=s, cursor_slice={})
-
-    def read_records(
-        self,
-        sync_mode: SyncMode,
-        cursor_field: List[str] = None,
-        stream_slice: Mapping[str, Any] = None,
-        stream_state: Mapping[str, Any] = None,
-    ) -> Iterable[Mapping[str, Any]]:
-        # The parent stream's records should always be read as full refresh
-        assert sync_mode == SyncMode.full_refresh
-
-        if not stream_slice:
-            result = self._records
-        else:
-            result = [
-                Record(data=r, associated_slice=stream_slice, stream_name=self.name)
-                for r in self._records
-                if r["slice"] == stream_slice["slice"]
-            ]
-
-        yield from result
-
-        # Update the state only after reading the full slice
-        cursor_field = self._stream_cursor_field.eval(config=self.config)
-        if stream_slice and cursor_field and result:
-            self._state["states"].append(
-                {cursor_field: result[-1][cursor_field], "partition": stream_slice["slice"]}
-            )
-
-    def get_json_schema(self) -> Mapping[str, Any]:
-        return {}
-
-
 class MockIncrementalStream(MockStream):
     def __init__(self, slices, records, name, cursor_field="", cursor=None, date_ranges=None):
         super().__init__(slices, records, name, cursor_field, cursor)