feat: Add Arrow types for efficient JSON data representation in pyarrow

db_dtypes/__init__.py

@@ -30,8 +30,8 @@
 
 from db_dtypes import core
 from db_dtypes.version import __version__
-from . import _versions_helpers
 
+from . import _versions_helpers
 
 date_dtype_name = "dbdate"
 time_dtype_name = "dbtime"
@@ -50,7 +50,7 @@
 # To use JSONArray and JSONDtype, you'll need Pandas 1.5.0 or later. With the removal
 # of Python 3.7 compatibility, the minimum Pandas version will be updated to 1.5.0.
 if packaging.version.Version(pandas.__version__) >= packaging.version.Version("1.5.0"):
-    from db_dtypes.json import JSONArray, JSONDtype
+    from db_dtypes.json import JSONArray, JSONArrowScalar, JSONArrowType, JSONDtype
 else:
     JSONArray = None
     JSONDtype = None
@@ -374,6 +374,8 @@ def __sub__(self, other):
         "DateDtype",
         "JSONDtype",
         "JSONArray",
+        "JSONArrowType",
+        "JSONArrowScalar",
         "TimeArray",
         "TimeDtype",
     ]

db_dtypes/json.py

@@ -64,6 +64,10 @@ def construct_array_type(cls):
         """Return the array type associated with this dtype."""
         return JSONArray
 
+    def __from_arrow__(self, array: pa.Array | pa.ChunkedArray) -> JSONArray:
+        """Convert the pyarrow array to the extension array."""
+        return JSONArray(array)
+
 
 class JSONArray(arrays.ArrowExtensionArray):
     """Extension array that handles BigQuery JSON data, leveraging a string-based
@@ -92,6 +96,10 @@ def __init__(self, values) -> None:
         else:
             raise NotImplementedError(f"Unsupported pandas version: {pd.__version__}")
 
+    def __arrow_array__(self):
+        """Convert to an arrow array. This is required for pyarrow extension."""
+        return self.pa_data
+
     @classmethod
     def _box_pa(
         cls, value, pa_type: pa.DataType | None = None
@@ -151,7 +159,12 @@ def _serialize_json(value):
     def _deserialize_json(value):
         """A static method that converts a JSON string back into its original value."""
         if not pd.isna(value):
-            return json.loads(value)
+            # Attempt to interpret the value as a JSON object.
+            # If it's not valid JSON, treat it as a regular string.
+            try:
+                return json.loads(value)
+            except json.JSONDecodeError:
+                return value
         else:
             return value
 
@@ -208,6 +221,8 @@ def __getitem__(self, item):
         value = self.pa_data[item]
         if isinstance(value, pa.ChunkedArray):
             return type(self)(value)
+        elif isinstance(value, pa.ExtensionScalar):
+            return value.as_py()
         else:
             scalar = JSONArray._deserialize_json(value.as_py())
             if scalar is None:
@@ -244,3 +259,36 @@ def __array__(self, dtype=None, copy: bool | None = None) -> np.ndarray:
         result[mask] = self._dtype.na_value
         result[~mask] = data[~mask].pa_data.to_numpy()
         return result
+
+
+class JSONArrowScalar(pa.ExtensionScalar):
+    def as_py(self):
+        return JSONArray._deserialize_json(self.value.as_py() if self.value else None)
+
+
+class JSONArrowType(pa.ExtensionType):
+    """Arrow extension type for the `dbjson` Pandas extension type."""
+
+    def __init__(self) -> None:
+        super().__init__(pa.string(), "dbjson")
+
+    def __arrow_ext_serialize__(self) -> bytes:
+        return b""
+
+    @classmethod
+    def __arrow_ext_deserialize__(cls, storage_type, serialized) -> JSONArrowType:
+        return JSONArrowType()
+
+    def __hash__(self) -> int:
+        return hash(str(self))
+
+    def to_pandas_dtype(self):
+        return JSONDtype()
+
+    def __arrow_ext_scalar_class__(self):
+        return JSONArrowScalar
+
+
+# Register the type to be included in RecordBatches, sent over IPC and received in
+# another Python process.
+pa.register_extension_type(JSONArrowType())

tests/compliance/json/test_json_compliance.py

@@ -22,10 +22,6 @@
 import pytest
 
 
-class TestJSONArrayAccumulate(base.BaseAccumulateTests):
-    pass
-
-
 class TestJSONArrayCasting(base.BaseCastingTests):
     def test_astype_str(self, data):
         # Use `json.dumps(str)` instead of passing `str(obj)` directly to the super method.

tests/unit/test_json.py

@@ -13,9 +13,11 @@
 # limitations under the License.
 
 import json
+import math
 
 import numpy as np
 import pandas as pd
+import pyarrow as pa
 import pytest
 
 import db_dtypes
@@ -36,7 +38,7 @@
         "null_field": None,
         "order": {
             "items": ["book", "pen", "computer"],
-            "total": 15.99,
+            "total": 15,
             "address": {"street": "123 Main St", "city": "Anytown"},
         },
     },
@@ -114,3 +116,117 @@ def test_as_numpy_array():
         ]
     )
     pd._testing.assert_equal(result, expected)
+
+
+def test_json_arrow_storage_type():
+    arrow_json_type = db_dtypes.JSONArrowType()
+    assert arrow_json_type.extension_name == "dbjson"
+    assert pa.types.is_string(arrow_json_type.storage_type)
+
+
+def test_json_arrow_constructors():
+    data = [
+        json.dumps(value, sort_keys=True, separators=(",", ":"))
+        for value in JSON_DATA.values()
+    ]
+    storage_array = pa.array(data, type=pa.string())
+
+    arr_1 = db_dtypes.JSONArrowType().wrap_array(storage_array)
+    assert isinstance(arr_1, pa.ExtensionArray)
+
+    arr_2 = pa.ExtensionArray.from_storage(db_dtypes.JSONArrowType(), storage_array)
+    assert isinstance(arr_2, pa.ExtensionArray)
+
+    assert arr_1 == arr_2
+
+
+def test_json_arrow_to_pandas():
+    data = [
+        json.dumps(value, sort_keys=True, separators=(",", ":"))
+        for value in JSON_DATA.values()
+    ]
+    arr = pa.array(data, type=db_dtypes.JSONArrowType())
+
+    s = arr.to_pandas()
+    assert isinstance(s.dtypes, db_dtypes.JSONDtype)
+    assert s[0]
+    assert s[1] == 100
+    assert math.isclose(s[2], 0.98)
+    assert s[3] == "hello world"
+    assert math.isclose(s[4][0], 0.1)
+    assert math.isclose(s[4][1], 0.2)
+    assert s[5] == {
+        "null_field": None,
+        "order": {
+            "items": ["book", "pen", "computer"],
+            "total": 15,
+            "address": {"street": "123 Main St", "city": "Anytown"},
+        },
+    }
+    assert pd.isna(s[6])
+
+
+def test_json_arrow_to_pylist():
+    data = [
+        json.dumps(value, sort_keys=True, separators=(",", ":"))
+        for value in JSON_DATA.values()
+    ]
+    arr = pa.array(data, type=db_dtypes.JSONArrowType())
+
+    s = arr.to_pylist()
+    assert isinstance(s, list)
+    assert s[0]
+    assert s[1] == 100
+    assert math.isclose(s[2], 0.98)
+    assert s[3] == "hello world"
+    assert math.isclose(s[4][0], 0.1)
+    assert math.isclose(s[4][1], 0.2)
+    assert s[5] == {
+        "null_field": None,
+        "order": {
+            "items": ["book", "pen", "computer"],
+            "total": 15,
+            "address": {"street": "123 Main St", "city": "Anytown"},
+        },
+    }
+    assert s[6] is None
+
+
+def test_json_arrow_record_batch():
+    data = [
+        json.dumps(value, sort_keys=True, separators=(",", ":"))
+        for value in JSON_DATA.values()
+    ]
+    arr = pa.array(data, type=db_dtypes.JSONArrowType())
+    batch = pa.RecordBatch.from_arrays([arr], ["json_col"])
+    sink = pa.BufferOutputStream()
+
+    with pa.RecordBatchStreamWriter(sink, batch.schema) as writer:
+        writer.write_batch(batch)
+
+    buf = sink.getvalue()
+
+    with pa.ipc.open_stream(buf) as reader:
+        result = reader.read_all()
+
+    json_col = result.column("json_col")
+    assert isinstance(json_col.type, db_dtypes.JSONArrowType)
+
+    s = json_col.to_pylist()
+
+    assert isinstance(s, list)
+    assert s[0]
+    assert s[1] == 100
+    assert math.isclose(s[2], 0.98)
+    assert s[3] == "hello world"
+    assert math.isclose(s[4][0], 0.1)
+    assert math.isclose(s[4][1], 0.2)
+    assert s[5] == {
+        "null_field": None,
+        "order": {
+            "items": ["book", "pen", "computer"],
+            "total": 15,
+            "address": {"street": "123 Main St", "city": "Anytown"},
+        },
+    }
+    assert s[6] is None