Add support of new JsonProviders in Flask 2.2+

Author: insspb

flask_mongoengine/json.py

@@ -1,18 +1,43 @@
+"""Flask application JSON extension functions."""
+from functools import lru_cache
+
 from bson import DBRef, ObjectId, json_util
-from flask.json import JSONEncoder
 from mongoengine.base import BaseDocument
 from mongoengine.queryset import QuerySet
 from pymongo.command_cursor import CommandCursor
 
 
+@lru_cache(maxsize=1)
+def use_json_provider() -> bool:
+    """Split Flask before 2.2.0 and after, to use/not use JSON provider approach."""
+    from flask import __version__
+
+    version = list(__version__.split("."))
+    return int(version[0]) > 2 or (int(version[0]) == 2 and int(version[1]) > 1)
+
+
 def _make_encoder(superclass):
+    """Extend Flask JSON Encoder 'default' method with support of Mongo objects."""
+    import warnings
+
+    warnings.warn(
+        (
+            "JSONEncoder/JSONDecoder are deprecated in Flask 2.2 and will be removed "
+            "in Flask 2.3."
+        ),
+        DeprecationWarning,
+        stacklevel=2,
+    )
+
     class MongoEngineJSONEncoder(superclass):
         """
         A JSONEncoder which provides serialization of MongoEngine
         documents and queryset objects.
         """
 
+        # noinspection PyProtectedMember, DuplicatedCode
         def default(self, obj):
+            """Extend JSONEncoder default method, with Mongo objects."""
             if isinstance(obj, BaseDocument):
                 return json_util._json_convert(obj.to_mongo())
             elif isinstance(obj, QuerySet):
@@ -28,7 +53,44 @@ def default(self, obj):
     return MongoEngineJSONEncoder
 
 
-MongoEngineJSONEncoder = _make_encoder(JSONEncoder)
+def _update_json_provider(superclass):
+    """Extend Flask Provider 'default' static method with support of Mongo objects."""
+
+    class MongoEngineJSONProvider(superclass):
+        """A JSON Provider update for Flask 2.2.0+"""
+
+        # noinspection PyProtectedMember, DuplicatedCode
+        @staticmethod
+        def default(obj):
+            """Extend JSONProvider default static method, with Mongo objects."""
+            if isinstance(obj, BaseDocument):
+                return json_util._json_convert(obj.to_mongo())
+            elif isinstance(obj, QuerySet):
+                return json_util._json_convert(obj.as_pymongo())
+            elif isinstance(obj, CommandCursor):
+                return json_util._json_convert(obj)
+            elif isinstance(obj, DBRef):
+                return obj.id
+            elif isinstance(obj, ObjectId):
+                return obj.__str__()
+            return super().default(obj)
+
+    return MongoEngineJSONProvider
+
+
+# Compatibility code for Flask 2.2.0+ support
+MongoEngineJSONEncoder = None
+MongoEngineJSONProvider = None
+
+if use_json_provider():
+    from flask.json.provider import DefaultJSONProvider
+
+    MongoEngineJSONProvider = _update_json_provider(DefaultJSONProvider)
+else:
+    from flask.json import JSONEncoder
+
+    MongoEngineJSONEncoder = _make_encoder(JSONEncoder)
+# End of compatibility code
 
 
 def override_json_encoder(app):
@@ -42,4 +104,9 @@ def override_json_encoder(app):
     NOTE: This does not cover situations where users override
     an instance's json_encoder after calling init_app.
     """
-    app.json_encoder = _make_encoder(app.json_encoder)
+
+    if use_json_provider():
+        app.json_provider_class = _update_json_provider(app.json_provider_class)
+        app.json = app.json_provider_class(app)
+    else:
+        app.json_encoder = _make_encoder(app.json_encoder)

tests/test_json.py

@@ -1,12 +1,18 @@
+"""Extension of app JSON capabilities."""
 import flask
 import pytest
 
 from flask_mongoengine import MongoEngine
+from flask_mongoengine.json import use_json_provider
 
 
 @pytest.fixture()
 def extended_db(app):
-    app.json_encoder = DummyEncoder
+    """Provider config fixture."""
+    if use_json_provider():
+        app.json_provider_class = DummyProvider
+    else:
+        app.json_encoder = DummyEncoder
     app.config["MONGODB_SETTINGS"] = [
         {
             "db": "flask_mongoengine_test_db",
@@ -43,11 +49,29 @@ class DummyEncoder(flask.json.JSONEncoder):
     """
 
 
+DummyProvider = None
+if use_json_provider():
+
+    class DummyProvider(flask.json.provider.DefaultJSONProvider):
+        """Dummy Provider, to test correct MRO in new flask versions."""
+
+
+@pytest.mark.skipif(condition=use_json_provider(), reason="New flask use other test")
 @pytest.mark.usefixtures("extended_db")
-def test_inheritance(app):
+def test_inheritance_old_flask(app):
     assert issubclass(app.json_encoder, DummyEncoder)
     json_encoder_name = app.json_encoder.__name__
 
-    # Since the class is dynamically derrived, must compare class names
-    # rather than class objects.
     assert json_encoder_name == "MongoEngineJSONEncoder"
+
+
+@pytest.mark.skipif(
+    condition=not use_json_provider(), reason="Old flask use other test"
+)
+@pytest.mark.usefixtures("extended_db")
+def test_inheritance(app):
+    assert issubclass(app.json_provider_class, DummyProvider)
+    json_provider_class = app.json_provider_class.__name__
+
+    assert json_provider_class == "MongoEngineJSONProvider"
+    assert isinstance(app.json, DummyProvider)