Fixed bug when fetching an empty CLOB or BLOB column marked with the

"IS JSON" constraint (#429).

doc/src/release_notes.rst

@@ -34,6 +34,13 @@ Thick Mode Changes
 #)  Fixed bug resulting in a segfault when using external authentication
     (`issue 425 <https://github.com/oracle/python-oracledb/issues/425>`__).
 
+Common Changes
+++++++++++++++
+
+#)  Fixed bug when fetching an empty CLOB or BLOB column marked with the
+    ``IS JSON`` constraint
+    (`issue 429 <https://github.com/oracle/python-oracledb/issues/429>`__).
+
 
 oracledb 2.5.0 (November 2024)
 ------------------------------

src/oracledb/impl/base/cursor.pyx

@@ -136,7 +136,8 @@ cdef class BaseCursorImpl:
                 value = value.read()
             if isinstance(value, bytes):
                 value = value.decode()
-            return json.loads(value)
+            if value:
+                return json.loads(value)
         return converter
 
     cdef int _check_binds(self, uint32_t num_execs) except -1:

src/oracledb/impl/thin/cursor.pyx

@@ -256,7 +256,8 @@ cdef class AsyncThinCursorImpl(BaseThinCursorImpl):
                 value = await value.read()
             if isinstance(value, bytes):
                 value = value.decode()
-            return json.loads(value)
+            if value:
+                return json.loads(value)
         return converter
 
     async def _fetch_rows_async(self, object cursor):

tests/sql/create_schema.sql

@@ -613,6 +613,10 @@ insert into &main_user..TestJsonCols values (1,
     '[1, 2, 3]', '[4, 5, 6]', utl_raw.cast_to_raw('[7, 8, 9]'))
 /
 
+insert into &main_user..TestJsonCols values (2,
+    'null', empty_clob(), empty_blob())
+/
+
 commit
 /
 

tests/test_4300_cursor_other.py

@@ -887,9 +887,12 @@ def test_4359(self):
     )
     def test_4360(self):
         "4360 - fetch JSON columns as Python objects"
-        expected_data = (1, [1, 2, 3], [4, 5, 6], [7, 8, 9])
-        self.cursor.execute("select * from TestJsonCols")
-        self.assertEqual(self.cursor.fetchone(), expected_data)
+        expected_data = [
+            (1, [1, 2, 3], [4, 5, 6], [7, 8, 9]),
+            (2, None, None, None),
+        ]
+        self.cursor.execute("select * from TestJsonCols order by IntCol")
+        self.assertEqual(self.cursor.fetchall(), expected_data)
 
     @unittest.skipIf(
         test_env.get_server_version() < (23, 1), "unsupported database"

tests/test_6300_cursor_other_async.py

@@ -863,6 +863,15 @@ async def test_6350(self):
         (fetched_value,) = await self.cursor.fetchone()
         self.assertEqual(fetched_value, value)
 
+    async def test_6351(self):
+        "4360 - fetch JSON columns as Python objects"
+        expected_data = [
+            (1, [1, 2, 3], [4, 5, 6], [7, 8, 9]),
+            (2, None, None, None),
+        ]
+        await self.cursor.execute("select * from TestJsonCols order by IntCol")
+        self.assertEqual(await self.cursor.fetchall(), expected_data)
+
 
 if __name__ == "__main__":
     test_env.run_test_cases()