feat: Add warning when user tries to access struct series fields with __getitem__

bigframes/core/indexers.py

@@ -16,6 +16,7 @@
 
 import typing
 from typing import Tuple, Union
+import warnings
 
 import bigframes_vendored.constants as constants
 import ibis
@@ -27,6 +28,8 @@
 import bigframes.core.indexes as indexes
 import bigframes.core.scalar
 import bigframes.dataframe
+import bigframes.dtypes
+import bigframes.exceptions
 import bigframes.operations as ops
 import bigframes.series
 
@@ -370,6 +373,7 @@ def _perform_loc_list_join(
     # right join based on the old index so that the matching rows from the user's
     # original dataframe will be duplicated and reordered appropriately
     if isinstance(series_or_dataframe, bigframes.series.Series):
+        _struct_accessor_check_and_warn(series_or_dataframe, keys_index)
         original_name = series_or_dataframe.name
         name = series_or_dataframe.name if series_or_dataframe.name is not None else "0"
         result = typing.cast(
@@ -391,6 +395,25 @@ def _perform_loc_list_join(
     return result
 
 
+def _struct_accessor_check_and_warn(
+    series: bigframes.series.Series, index: indexes.Index
+):
+    if not bigframes.dtypes.is_struct_like(series.dtype):
+        # No need to check series that do not have struct values
+        return
+
+    if not bigframes.dtypes.is_string_like(index.dtype):
+        # No need to check indexing with non-string values.
+        return
+
+    if not bigframes.dtypes.is_string_like(series.index.dtype):
+        warnings.warn(
+            "Are you trying to access struct fields? If so, please use Series.struct.field(...) method instead.",
+            category=bigframes.exceptions.IncorrectApiUsageWarning,
+            stacklevel=7,  # Stack depth from series.__getitem__ to here
+        )
+
+
 @typing.overload
 def _iloc_getitem_series_or_dataframe(
     series_or_dataframe: bigframes.series.Series, key

bigframes/exceptions.py

@@ -73,3 +73,7 @@ class UnknownDataTypeWarning(Warning):
 
 class ApiDeprecationWarning(FutureWarning):
     """The API has been deprecated."""
+
+
+class IncorrectApiUsageWarning(Warning):
+    """The API is not being used in a correct way."""

tests/system/small/core/__init__.py

@@ -0,0 +1,13 @@
+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.

tests/system/small/core/test_indexers.py

@@ -0,0 +1,94 @@
+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import warnings
+
+import pyarrow as pa
+import pytest
+
+import bigframes.exceptions
+import bigframes.pandas as bpd
+
+
+@pytest.fixture(scope="module")
+def string_indexed_struct_series(session):
+    return bpd.Series(
+        [
+            {"project": "pandas", "version": 1},
+        ],
+        dtype=bpd.ArrowDtype(
+            pa.struct([("project", pa.string()), ("version", pa.int64())])
+        ),
+        index=["a"],
+        session=session,
+    )
+
+
+@pytest.fixture(scope="module")
+def number_series(session):
+    return bpd.Series(
+        [0],
+        dtype=bpd.Int64Dtype,
+        session=session,
+    )
+
+
+@pytest.fixture(scope="module")
+def string_indexed_number_series(session):
+    return bpd.Series(
+        [0],
+        dtype=bpd.Int64Dtype,
+        index=["a"],
+        session=session,
+    )
+
+
+def test_non_string_indexed_struct_series_with_string_key_should_warn(session):
+    s = bpd.Series(
+        [
+            {"project": "pandas", "version": 1},
+        ],
+        dtype=bpd.ArrowDtype(
+            pa.struct([("project", pa.string()), ("version", pa.int64())])
+        ),
+        session=session,
+    )
+
+    with pytest.warns(bigframes.exceptions.IncorrectApiUsageWarning):
+        s["a"]
+
+
+@pytest.mark.parametrize(
+    "series",
+    [
+        "string_indexed_struct_series",
+        "number_series",
+        "string_indexed_number_series",
+    ],
+)
+@pytest.mark.parametrize(
+    "key",
+    [
+        0,
+        "a",
+    ],
+)
+def test_struct_series_indexers_should_not_warn(request, series, key):
+    s = request.getfixturevalue(series)
+
+    with warnings.catch_warnings():
+        warnings.simplefilter(
+            "error", category=bigframes.exceptions.IncorrectApiUsageWarning
+        )
+        s[key]