fix json nullable column

ormar/fields/model_fields.py

@@ -168,7 +168,7 @@ class ModelFieldFactory:
             unique=kwargs.pop("unique", False),
             pydantic_only=pydantic_only,
             autoincrement=autoincrement,
-            column_type=cls.get_column_type(**kwargs),
+            column_type=cls.get_column_type(**kwargs, sql_nullable=sql_nullable),
             choices=choices,
             encrypt_secret=encrypt_secret,
             encrypt_backend=encrypt_backend,
@@ -516,7 +516,7 @@ class JSON(ModelFieldFactory, pydantic.Json):
         :return: initialized column with proper options
         :rtype: sqlalchemy Column
         """
-        return sqlalchemy.JSON()
+        return sqlalchemy.JSON(none_as_null=kwargs.get("sql_nullable", False))
 
 
 if TYPE_CHECKING:  # pragma: nocover # noqa: C901

ormar/fields/parsers.py

@@ -2,7 +2,7 @@ import base64
 import datetime
 import decimal
 import uuid
-from typing import Any, Callable, Dict, Union
+from typing import Any, Callable, Dict, Optional, Union
 
 import pydantic
 from pydantic.datetime_parse import parse_date, parse_datetime, parse_time
@@ -37,7 +37,7 @@ def encode_bytes(value: Union[str, bytes], represent_as_string: bool = False) ->
     return value if isinstance(value, bytes) else value.encode("utf-8")
 
 
-def encode_json(value: Any) -> str:
+def encode_json(value: Any) -> Optional[str]:
     value = json.dumps(value) if not isinstance(value, str) else re_dump_value(value)
     value = value.decode("utf-8") if isinstance(value, bytes) else value
     return value

ormar/models/newbasemodel.py

@@ -22,14 +22,11 @@ from typing import (
 import databases
 import pydantic
 import sqlalchemy
+
+from ormar.fields.parsers import encode_json
 from ormar.models.utils import Extra
 from pydantic import BaseModel
 
-try:
-    import orjson as json
-except ImportError:  # pragma: no cover
-    import json  # type: ignore
-
 
 import ormar  # noqa I100
 from ormar.exceptions import ModelError, ModelPersistenceError
@@ -925,12 +922,7 @@ class NewBaseModel(pydantic.BaseModel, ModelTableProxy, metaclass=ModelMetaclass
         """
         if column_name not in self._json_fields:
             return value
-        if not isinstance(value, str):
-            try:
-                value = json.dumps(value)
-            except TypeError:  # pragma no cover
-                pass
-        return value.decode("utf-8") if isinstance(value, bytes) else value
+        return encode_json(value)
 
     def _extract_own_model_fields(self) -> Dict:
         """

tests/test_queries/test_isnull_filter.py

@@ -34,6 +34,18 @@ class Book(ormar.Model):
     year: int = ormar.Integer(nullable=True)
 
 
+class JsonModel(ormar.Model):
+    class Meta(ormar.ModelMeta):
+        metadata = metadata
+        database = database
+        tablename = "jsons"
+
+    id = ormar.Integer(primary_key=True)
+    text_field = ormar.Text(nullable=True)
+    json_field = ormar.JSON(nullable=True)
+    json_not_null = ormar.JSON()
+
+
 @pytest.fixture(autouse=True, scope="module")
 def create_test_database():
     engine = sqlalchemy.create_engine(DATABASE_URL)
@@ -83,3 +95,16 @@ async def test_is_null():
         assert len(tolkien.books) == 2
         assert tolkien.books[0].year == 1955
         assert tolkien.books[0].title == "The Lord of the Rings"
+
+
+@pytest.mark.asyncio
+async def test_isnull_json():
+    async with database:
+        author = await JsonModel.objects.create(json_not_null=None)
+        assert author.json_field is None
+        non_null_text_fields = await JsonModel.objects.all(text_field__isnull=False)
+        assert len(non_null_text_fields) == 0
+        non_null_json_fields = await JsonModel.objects.all(json_field__isnull=False)
+        assert len(non_null_json_fields) == 0
+        non_null_json_fields = await JsonModel.objects.all(json_not_null__isnull=False)
+        assert len(non_null_json_fields) == 1