fix: allow parsing json in dynamic queries

duckdb_engine/__init__.py

@@ -28,6 +28,7 @@
 )
 from sqlalchemy.dialects.postgresql.psycopg2 import PGDialect_psycopg2
 from sqlalchemy.engine.default import DefaultDialect
+from sqlalchemy.engine.interfaces import Dialect as RootDialect
 from sqlalchemy.engine.reflection import cache
 from sqlalchemy.engine.url import URL
 from sqlalchemy.exc import NoSuchTableError
@@ -47,7 +48,7 @@
 if TYPE_CHECKING:
     from sqlalchemy.base import Connection
     from sqlalchemy.engine.interfaces import _IndexDict
-
+    from sqlalchemy.sql.type_api import _ResultProcessor
 
 register_extension_types()
 
@@ -215,6 +216,16 @@ def quote_schema(self, schema: str, force: Any = None) -> str:
         return self.format_schema(schema)
 
 
+class DuckDBNullType(sqltypes.NullType):
+    def result_processor(
+        self, dialect: RootDialect, coltype: sqltypes.TypeEngine
+    ) -> Optional["_ResultProcessor"]:
+        if coltype == "JSON":
+            return sqltypes.JSON().result_processor(dialect, coltype)
+        else:
+            return super().result_processor(dialect, coltype)
+
+
 class Dialect(PGDialect_psycopg2):
     name = "duckdb"
     driver = "duckdb_engine"
@@ -247,6 +258,14 @@ def __init__(self, *args: Any, **kwargs: Any) -> None:
         kwargs["use_native_hstore"] = False
         super().__init__(*args, **kwargs)
 
+    def type_descriptor(self, typeobj: Type[sqltypes.TypeEngine]) -> Any:  # type: ignore[override]
+        res = super().type_descriptor(typeobj)
+
+        if isinstance(res, sqltypes.NullType):
+            return DuckDBNullType()
+
+        return res
+
     def connect(self, *cargs: Any, **cparams: Any) -> "Connection":
         core_keys = get_core_config()
         preload_extensions = cparams.pop("preload_extensions", [])

duckdb_engine/datatypes.py

@@ -188,6 +188,7 @@ def __init__(self, fields: Dict[str, TV]):
     "timestamp_ms": sqltypes.TIMESTAMP,
     "timestamp_ns": sqltypes.TIMESTAMP,
     "enum": sqltypes.Enum,
+    "json": sqltypes.JSON,
 }
 
 

duckdb_engine/tests/test_datatypes.py

@@ -45,6 +45,18 @@ def test_unsigned_integer_type(
     assert session.query(table).one()
 
 
+@mark.remote_data()
+def test_raw_json(engine: Engine) -> None:
+    importorskip("duckdb", "0.9.3.dev4040")
+
+    with engine.connect() as conn:
+        assert conn.execute(text("load json"))
+
+        assert conn.execute(text("select {'Hello': 'world'}::JSON")).fetchone() == (
+            {"Hello": "world"},
+        )
+
+
 def test_json(engine: Engine, session: Session) -> None:
     base = declarative_base()