introduce preliminary complex type conversion

Signed-off-by: varun-edachali-dbx <varun.edachali@databricks.com>

Author: varun-edachali-dbx

src/databricks/sql/result_set.py

@@ -600,6 +600,43 @@ def fetchall_json(self) -> List:
 
         return results
 
+    def _convert_complex_types_to_string(
+        self, rows: "pyarrow.Table"
+    ) -> "pyarrow.Table":
+        """
+        Convert complex types (array, struct, map) to string representation.
+
+        Args:
+            rows: Input PyArrow table
+
+        Returns:
+            PyArrow table with complex types converted to strings
+        """
+
+        if not pyarrow:
+            return rows
+
+        def convert_complex_column_to_string(col: "pyarrow.Array") -> "pyarrow.Array":
+            python_values = col.to_pylist()
+            json_strings = [
+                (None if val is None else json.dumps(val)) for val in python_values
+            ]
+            return pyarrow.array(json_strings, type=pyarrow.string())
+
+        converted_columns = []
+        for col in rows.columns:
+            converted_col = col
+            if (
+                pyarrow.types.is_list(col.type)
+                or pyarrow.types.is_large_list(col.type)
+                or pyarrow.types.is_struct(col.type)
+                or pyarrow.types.is_map(col.type)
+            ):
+                converted_col = convert_complex_column_to_string(col)
+            converted_columns.append(converted_col)
+
+        return pyarrow.Table.from_arrays(converted_columns, names=rows.column_names)
+
     def fetchmany_arrow(self, size: int) -> "pyarrow.Table":
         """
         Fetch the next set of rows as an Arrow table.
@@ -625,6 +662,9 @@ def fetchmany_arrow(self, size: int) -> "pyarrow.Table":
         results = self._convert_json_to_arrow(rows)
         self._next_row_index += results.num_rows
 
+        if not self.backend._use_arrow_native_complex_types:
+            results = self._convert_complex_types_to_string(results)
+
         return results
 
     def fetchall_arrow(self) -> "pyarrow.Table":
@@ -639,6 +679,9 @@ def fetchall_arrow(self) -> "pyarrow.Table":
         results = self._convert_json_to_arrow(rows)
         self._next_row_index += results.num_rows
 
+        if not self.backend._use_arrow_native_complex_types:
+            results = self._convert_complex_types_to_string(results)
+
         return results
 
     def fetchone(self) -> Optional[Row]: