feat: implement basic struct handling

README.md

@@ -22,11 +22,13 @@ or Velox.
 ### Locally
 To run the gateway locally - you need to setup a Python (Conda) environment.
 
+To run the Spark tests you will need Java installed.
+
 Ensure you have [Miniconda](https://docs.anaconda.com/miniconda/miniconda-install/) and [Rust/Cargo](https://doc.rust-lang.org/cargo/getting-started/installation.html) installed.
 
 Once that is done - run these steps from a bash terminal:
 ```bash
-git clone --recursive https://github.com/<your-fork>/spark-substrait-gateway.git
+git clone https://github.com/<your-fork>/spark-substrait-gateway.git
 cd spark-substrait-gateway
 conda init bash
 . ~/.bashrc

environment.yml

@@ -11,7 +11,7 @@ dependencies:
   - setuptools >= 61.0.0
   - setuptools_scm >= 6.2.0
   - mypy-protobuf
-  - types-protobuf >= 4.25.0, < 5.0.0
+  - types-protobuf >= 5.0.0
   - numpy < 2.0.0
   - Faker
   - pip:
@@ -27,7 +27,7 @@ dependencies:
     - substrait == 0.21.0
     - substrait-validator
     - pytest-timeout
-    - protobuf >= 4.25.3, < 5.0.0
+    - protobuf >= 5.0.0
     - cryptography == 43.0.*
     - click == 8.1.*
     - pyjwt == 2.8.*

src/backends/arrow_tools.py

@@ -0,0 +1,51 @@
+# SPDX-License-Identifier: Apache-2.0
+"""Routines to manipulate arrow tables."""
+import pyarrow as pa
+
+
+def _reapply_names_to_type(array: pa.ChunkedArray, names: list[str]) -> (pa.Array, list[str]):
+    new_arrays = []
+    new_schema = []
+
+    if array.type.num_fields > len(names):
+        raise ValueError('Insufficient number of names provided to reapply names.')
+
+    remaining_names = names
+    if pa.types.is_list(array.type):
+        raise NotImplementedError('Reapplying names to lists not yet supported')
+    if pa.types.is_map(array.type):
+        raise NotImplementedError('Reapplying names to maps not yet supported')
+    if pa.types.is_struct(array.type):
+        field_num = 0
+        while field_num < array.type.num_fields:
+            field = array.chunks[0].field(field_num)
+            this_name = remaining_names.pop(0)
+
+            new_array, remaining_names = _reapply_names_to_type(field, remaining_names)
+            new_arrays.append(new_array)
+
+            new_schema.append(pa.field(this_name, new_array.type))
+
+            field_num += 1
+
+        return pa.StructArray.from_arrays(new_arrays, fields=new_schema), remaining_names
+    if array.type.num_fields != 0:
+        raise ValueError(f'Unsupported complex type: {array.type}')
+    return array, remaining_names
+
+
+def reapply_names(table: pa.Table, names: list[str]) -> pa.Table:
+    """Apply the provided names to the given table recursively."""
+    new_arrays = []
+    new_schema = []
+
+    remaining_names = names
+    for column in iter(table.columns):
+        this_name = remaining_names.pop(0)
+
+        new_array, remaining_names = _reapply_names_to_type(column, remaining_names)
+        new_arrays.append(new_array)
+
+        new_schema.append(pa.field(this_name, new_array.type))
+
+    return pa.Table.from_arrays(new_arrays, schema=pa.schema(new_schema))

src/backends/duckdb_backend.py

@@ -11,6 +11,7 @@
 from substrait.gen.proto import plan_pb2
 
 from backends.backend import Backend
+from src.backends.arrow_tools import reapply_names
 from transforms.rename_functions import RenameFunctionsForDuckDB
 
 
@@ -73,7 +74,8 @@ def _execute_plan(self, plan: plan_pb2.Plan) -> pa.lib.Table:
             query_result = self._connection.from_substrait(proto=plan_data)
         except Exception as err:
             raise ValueError(f"DuckDB Execution Error: {err}") from err
-        return query_result.arrow()
+        arrow = query_result.arrow()
+        return reapply_names(arrow, plan.relations[0].root.names)
 
     def register_table(
         self,

src/backends/tests/arrow_tools_test.py

@@ -0,0 +1,56 @@
+# SPDX-License-Identifier: Apache-2.0
+from dataclasses import dataclass
+
+import pyarrow as pa
+import pytest
+
+from src.backends.arrow_tools import reapply_names
+
+
+@dataclass
+class TestCase:
+    name: str
+    input: pa.Table
+    names: list[str]
+    expected: pa.table
+
+
+cases: list[TestCase] = [
+    TestCase('empty table', pa.Table.from_arrays([]), ['a', 'b'], pa.Table.from_arrays([])),
+    TestCase('normal columns',
+             pa.Table.from_pydict(
+                 {"name": [None, "Joe", "Sarah", None], "age": [99, None, 42, None]},
+                 schema=pa.schema({"name": pa.string(), "age": pa.int32()})
+             ),
+             ['renamed_name', 'renamed_age'],
+             pa.Table.from_pydict(
+                 {"renamed_name": [None, "Joe", "Sarah", None],
+                  "renamed_age": [99, None, 42, None]},
+                 schema=pa.schema({"renamed_name": pa.string(), "renamed_age": pa.int32()})
+             )),
+    TestCase('struct column',
+             pa.Table.from_arrays(
+                 [pa.array([{"": 1, "b": "b"}],
+                           type=pa.struct([("", pa.int64()), ("b", pa.string())]))],
+                 names=["r"]),
+             ['r', 'a', 'b'],
+             pa.Table.from_arrays(
+                 [pa.array([{"a": 1, "b": "b"}],
+                           type=pa.struct([("a", pa.int64()), ("b", pa.string())]))], names=["r"])
+             ),
+    TestCase('nested structs', pa.Table.from_arrays([]), ['a', 'b'], pa.Table.from_arrays([])),
+    # TODO -- Test a list.
+    # TODO -- Test a map.
+    # TODO -- Test a mixture of complex and simple types.
+]
+
+
+class TestArrowTools:
+    """Tests the functionality of the arrow tools package."""
+
+    @pytest.mark.parametrize(
+        "case", cases, ids=lambda case: case.name
+    )
+    def test_reapply_names(self, case):
+        result = reapply_names(case.input, case.names)
+        assert result == case.expected

src/gateway/converter/conversion_options.py

@@ -11,7 +11,7 @@
 class ConversionOptions:
     """Holds all the possible conversion options."""
 
-    def __init__(self, backend: BackendOptions = None):
+    def __init__(self, backend: BackendOptions):
         """Initialize the conversion options."""
         self.use_named_table_workaround = False
         self.needs_scheme_in_path_uris = False