Polaris JSON Read Writer, Unit Test, Materilization.

examples/polars/materialization/my_script.py

@@ -47,12 +47,20 @@
         file="./df.parquet",
         combine=df_builder,
     ),
+    # materialize the dataframe to a feather file
     to.feather(
         dependencies=output_columns,
         id="df_to_feather",
         file="./df.feather",
         combine=df_builder,
     ),
+    # materialize the dataframe to a json file
+    to.json(
+        dependencies=output_columns,
+        id="df_to_json",
+        file="./df.json",
+        combine=df_builder,
+    ),
 ]
 # Visualize what is happening
 dr.visualize_materialization(
@@ -68,9 +76,11 @@
     additional_vars=[
         "df_to_parquet_build_result",
         "df_to_feather_build_result",
+        "df_to_json_build_result",
     ],  # because combine is used, we can get that result here.
     inputs=initial_columns,
 )
 print(materialization_results)
 print(additional_outputs["df_to_parquet_build_result"])
 print(additional_outputs["df_to_feather_build_result"])
+print(additional_outputs["df_to_json_build_result"])

hamilton/plugins/polars_extensions.py

@@ -1,6 +1,6 @@
 import dataclasses
 import sys
-from io import BytesIO, TextIOWrapper
+from io import BytesIO, IOBase, TextIOWrapper
 from pathlib import Path
 from typing import (
     Any,
@@ -31,7 +31,7 @@
 
 # for polars 0.18.0 we need to check what to do.
 if has_alias and hasattr(pl.type_aliases, "CsvEncoding"):
-    from polars.type_aliases import CsvEncoding
+    from polars.type_aliases import CsvEncoding, SchemaDefinition
 else:
     CsvEncoding = Type
 if has_alias and hasattr(pl.type_aliases, "CsvQuoteStyle"):
@@ -434,6 +434,71 @@ def name(cls) -> str:
         return "feather"
 
 
+@dataclasses.dataclass
+class PolarsJSONReader(DataLoader):
+    """
+    Class specifically to handle loading JSON files with Polars.
+    Should map to https://pola-rs.github.io/polars/py-polars/html/reference/api/polars.read_json.html
+    """
+
+    source: Union[str, Path, IOBase, bytes]
+    schema: SchemaDefinition = None
+    schema_overrides: SchemaDefinition = None
+
+    @classmethod
+    def applicable_types(cls) -> Collection[Type]:
+        return [DATAFRAME_TYPE]
+
+    def _get_loading_kwargs(self):
+        kwargs = {}
+        if self.schema is not None:
+            kwargs["schema"] = self.schema
+        if self.schema_overrides is not None:
+            kwargs["schema_overrides"] = self.schema_overrides
+        return kwargs
+
+    def load_data(self, type_: Type) -> Tuple[DATAFRAME_TYPE, Dict[str, Any]]:
+        df = pl.read_json(self.source, **self._get_loading_kwargs())
+        metadata = utils.get_file_metadata(self.source)
+        return df, metadata
+
+    @classmethod
+    def name(cls) -> str:
+        return "json"
+
+
+@dataclasses.dataclass
+class PolarsJSONWriter(DataSaver):
+    """
+    Class specifically to handle saving JSON files with Polars.
+    Should map to https://pola-rs.github.io/polars/py-polars/html/reference/api/polars.DataFrame.write_json.html
+    """
+
+    file: None = None
+    pretty: bool = False
+    row_oriented: bool = False
+
+    @classmethod
+    def applicable_types(cls) -> Collection[Type]:
+        return [DATAFRAME_TYPE]
+
+    def _get_saving_kwargs(self):
+        kwargs = {}
+        if self.pretty is not None:
+            kwargs["pretty"] = self.pretty
+        if self.row_oriented is not None:
+            kwargs["row_oriented"] = self.row_oriented
+        return kwargs
+
+    def save_data(self, data: DATAFRAME_TYPE) -> Dict[str, Any]:
+        data.write_json(self.file, **self._get_saving_kwargs())
+        return utils.get_file_metadata(self.file)
+
+    @classmethod
+    def name(cls) -> str:
+        return "json"
+
+
 def register_data_loaders():
     """Function to register the data loaders for this extension."""
     for loader in [
@@ -443,6 +508,8 @@ def register_data_loaders():
         PolarsParquetWriter,
         PolarsFeatherReader,
         PolarsFeatherWriter,
+        PolarsJSONReader,
+        PolarsJSONWriter,
     ]:
         registry.register_adapter(loader)
 

tests/plugins/test_polars_extensions.py

@@ -8,6 +8,8 @@
     PolarsCSVWriter,
     PolarsFeatherReader,
     PolarsFeatherWriter,
+    PolarsJSONReader,
+    PolarsJSONWriter,
     PolarsParquetReader,
     PolarsParquetWriter,
 )
@@ -73,3 +75,21 @@ def test_polars_feather(tmp_path: pathlib.Path) -> None:
     assert "compression" in write_kwargs
     assert file_path.exists()
     assert metadata["path"] == file_path
+
+
+def test_polars_json(df: pl.DataFrame, tmp_path: pathlib.Path) -> None:
+    file = tmp_path / "test.json"
+    writer = PolarsJSONWriter(file=file, pretty=True)
+    kwargs1 = writer._get_saving_kwargs()
+    writer.save_data(df)
+
+    reader = PolarsJSONReader(source=file)
+    kwargs2 = reader._get_loading_kwargs()
+    df2, metadata = reader.load_data(pl.DataFrame)
+
+    assert PolarsJSONWriter.applicable_types() == [pl.DataFrame]
+    assert PolarsJSONReader.applicable_types() == [pl.DataFrame]
+    assert kwargs1["pretty"]
+    assert df2.shape == (2, 2)
+    assert "schema" not in kwargs2
+    assert df.frame_equal(df2)