feat: add __hash__ property for JSONArrowType (#316)

Author: chelsea-lin

db_dtypes/json.py

@@ -274,6 +274,9 @@ def __arrow_ext_serialize__(self) -> bytes:
     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()
 

tests/unit/test_json.py

@@ -129,6 +129,11 @@ def test_json_arrow_storage_type():
     assert pa.types.is_string(arrow_json_type.storage_type)
 
 
+def test_json_arrow_hash():
+    arr = pa.array([], type=db_dtypes.JSONArrowType())
+    assert hash(arr.type) == hash(db_dtypes.JSONArrowType())
+
+
 def test_json_arrow_constructors():
     data = [
         json.dumps(value, sort_keys=True, separators=(",", ":"))