Include the backend in the serialization of the Narwhals dataframe to ensure that it can be deserialized.

ccflow/exttypes/narwhals.py

@@ -59,6 +59,13 @@ def validate_from_any(value: Any):
                 if source_args and source_args[0] and source_args[0] is not Any:
                     backend = source_args[0].__module__.split(".", 1)[0]
 
+                if "backend" in value:
+                    if backend is None:
+                        # backend in source args takes precedence
+                        backend = value["backend"]
+
+                    value = value["data"]
+
                 try:
                     try:
                         value = nw.from_dict(value, backend=backend)
@@ -89,7 +96,10 @@ def validate_from_any(value: Any):
 
         def serialize(value: Any):
             if isinstance(value, nw.DataFrame):
-                return value.to_dict(as_series=False)
+                return {
+                    "data": value.to_dict(as_series=False),
+                    "backend": value.implementation.value,
+                }
             else:
                 raise ValueError("Cannot serialize a LazyFrame to JSON. Please use the collect() method to convert it to a DataFrame first.")
 

ccflow/tests/result/test_narwhals.py

@@ -3,6 +3,7 @@
 import narwhals.stable.v1 as nw
 import polars as pl
 import pytest
+from polars.testing import assert_frame_equal
 
 from ccflow.exttypes.narwhals import (
     DataFrameT,
@@ -90,3 +91,10 @@ class MyNarwhalsResult(NarwhalsDataFrameResult):
     df = pl.DataFrame(data)
     result = MyNarwhalsResult(df=df)
     assert result.df.schema["d"] == nw.Float64()
+
+
+def test_serialization(data):
+    df = pl.DataFrame(data)
+    result = NarwhalsDataFrameResult(df=df)
+    result2 = NarwhalsDataFrameResult.model_validate_json(result.model_dump_json())
+    assert_frame_equal(result.df.to_native(), result2.df.to_native())