Fixed #29522 -- Refactored the Deserializer functions to classes.

Co-authored-by: Emad Mokhtar <[email protected]>

AUTHORS

@@ -68,7 +68,7 @@ answer newbie questions, and generally made Django that much better:
     Aljaž Košir <[email protected]>
     Aljosa Mohorovic <[email protected]>
     Alokik Vijay <[email protected]>
-    Amir Karimi <amk9978@gmail.com>
+    Amir Karimi <https://github.com/amk9978>
     Amit Chakradeo <https://amit.chakradeo.net/>
     Amit Ramon <[email protected]>
     Amit Upadhyay <http://www.amitu.com/blog/>

django/core/serializers/json.py

@@ -59,19 +59,27 @@ def getvalue(self):
         return super(PythonSerializer, self).getvalue()
 
 
-def Deserializer(stream_or_string, **options):
+class Deserializer(PythonDeserializer):
     """Deserialize a stream or string of JSON data."""
-    if not isinstance(stream_or_string, (bytes, str)):
-        stream_or_string = stream_or_string.read()
-    if isinstance(stream_or_string, bytes):
-        stream_or_string = stream_or_string.decode()
-    try:
-        objects = json.loads(stream_or_string)
-        yield from PythonDeserializer(objects, **options)
-    except (GeneratorExit, DeserializationError):
-        raise
-    except Exception as exc:
-        raise DeserializationError() from exc
+
+    def __init__(self, stream_or_string, **options):
+        if not isinstance(stream_or_string, (bytes, str)):
+            stream_or_string = stream_or_string.read()
+        if isinstance(stream_or_string, bytes):
+            stream_or_string = stream_or_string.decode()
+        try:
+            objects = json.loads(stream_or_string)
+        except Exception as exc:
+            raise DeserializationError() from exc
+        super().__init__(objects, **options)
+
+    def _handle_object(self, obj):
+        try:
+            yield from super()._handle_object(obj)
+        except (GeneratorExit, DeserializationError):
+            raise
+        except Exception as exc:
+            raise DeserializationError(f"Error deserializing object: {exc}") from exc
 
 
 class DjangoJSONEncoder(json.JSONEncoder):

django/core/serializers/jsonl.py

@@ -39,19 +39,30 @@ def getvalue(self):
         return super(PythonSerializer, self).getvalue()
 
 
-def Deserializer(stream_or_string, **options):
+class Deserializer(PythonDeserializer):
     """Deserialize a stream or string of JSON data."""
-    if isinstance(stream_or_string, bytes):
-        stream_or_string = stream_or_string.decode()
-    if isinstance(stream_or_string, (bytes, str)):
-        stream_or_string = stream_or_string.split("\n")
-
-    for line in stream_or_string:
-        if not line.strip():
-            continue
+
+    def __init__(self, stream_or_string, **options):
+        if isinstance(stream_or_string, bytes):
+            stream_or_string = stream_or_string.decode()
+        if isinstance(stream_or_string, str):
+            stream_or_string = stream_or_string.splitlines()
+        super().__init__(Deserializer._get_lines(stream_or_string), **options)
+
+    def _handle_object(self, obj):
         try:
-            yield from PythonDeserializer([json.loads(line)], **options)
+            yield from super()._handle_object(obj)
         except (GeneratorExit, DeserializationError):
             raise
         except Exception as exc:
-            raise DeserializationError() from exc
+            raise DeserializationError(f"Error deserializing object: {exc}") from exc
+
+    @staticmethod
+    def _get_lines(stream):
+        for line in stream:
+            if not line.strip():
+                continue
+            try:
+                yield json.loads(line)
+            except Exception as exc:
+                raise DeserializationError() from exc

django/core/serializers/python.py

@@ -96,45 +96,60 @@ def getvalue(self):
         return self.objects
 
 
-def Deserializer(
-    object_list, *, using=DEFAULT_DB_ALIAS, ignorenonexistent=False, **options
-):
+class Deserializer(base.Deserializer):
     """
     Deserialize simple Python objects back into Django ORM instances.
 
     It's expected that you pass the Python objects themselves (instead of a
     stream or a string) to the constructor
     """
-    handle_forward_references = options.pop("handle_forward_references", False)
-    field_names_cache = {}  # Model: <list of field_names>
 
-    for d in object_list:
+    def __init__(
+        self, object_list, *, using=DEFAULT_DB_ALIAS, ignorenonexistent=False, **options
+    ):
+        super().__init__(object_list, **options)
+        self.handle_forward_references = options.pop("handle_forward_references", False)
+        self.using = using
+        self.ignorenonexistent = ignorenonexistent
+        self.field_names_cache = {}  # Model: <list of field_names>
+        self._iterator = None
+
+    def __iter__(self):
+        for obj in self.stream:
+            yield from self._handle_object(obj)
+
+    def __next__(self):
+        if self._iterator is None:
+            self._iterator = iter(self)
+        return next(self._iterator)
+
+    def _handle_object(self, obj):
+        data = {}
+        m2m_data = {}
+        deferred_fields = {}
+
         # Look up the model and starting build a dict of data for it.
         try:
-            Model = _get_model(d["model"])
+            Model = self._get_model_from_node(obj["model"])
         except base.DeserializationError:
-            if ignorenonexistent:
-                continue
-            else:
-                raise
-        data = {}
-        if "pk" in d:
+            if self.ignorenonexistent:
+                return
+            raise
+        if "pk" in obj:
             try:
-                data[Model._meta.pk.attname] = Model._meta.pk.to_python(d.get("pk"))
+                data[Model._meta.pk.attname] = Model._meta.pk.to_python(obj.get("pk"))
             except Exception as e:
                 raise base.DeserializationError.WithData(
-                    e, d["model"], d.get("pk"), None
+                    e, obj["model"], obj.get("pk"), None
                 )
-        m2m_data = {}
-        deferred_fields = {}
 
-        if Model not in field_names_cache:
-            field_names_cache[Model] = {f.name for f in Model._meta.get_fields()}
-        field_names = field_names_cache[Model]
+        if Model not in self.field_names_cache:
+            self.field_names_cache[Model] = {f.name for f in Model._meta.get_fields()}
+        field_names = self.field_names_cache[Model]
 
         # Handle each field
-        for field_name, field_value in d["fields"].items():
-            if ignorenonexistent and field_name not in field_names:
+        for field_name, field_value in obj["fields"].items():
+            if self.ignorenonexistent and field_name not in field_names:
                 # skip fields no longer on model
                 continue
 
@@ -145,51 +160,59 @@ def Deserializer(
                 field.remote_field, models.ManyToManyRel
             ):
                 try:
-                    values = base.deserialize_m2m_values(
-                        field, field_value, using, handle_forward_references
-                    )
+                    values = self._handle_m2m_field_node(field, field_value)
+                    if values == base.DEFER_FIELD:
+                        deferred_fields[field] = field_value
+                    else:
+                        m2m_data[field.name] = values
                 except base.M2MDeserializationError as e:
                     raise base.DeserializationError.WithData(
-                        e.original_exc, d["model"], d.get("pk"), e.pk
+                        e.original_exc, obj["model"], obj.get("pk"), e.pk
                     )
-                if values == base.DEFER_FIELD:
-                    deferred_fields[field] = field_value
-                else:
-                    m2m_data[field.name] = values
+
             # Handle FK fields
             elif field.remote_field and isinstance(
                 field.remote_field, models.ManyToOneRel
             ):
                 try:
-                    value = base.deserialize_fk_value(
-                        field, field_value, using, handle_forward_references
-                    )
+                    value = self._handle_fk_field_node(field, field_value)
+                    if value == base.DEFER_FIELD:
+                        deferred_fields[field] = field_value
+                    else:
+                        data[field.attname] = value
                 except Exception as e:
                     raise base.DeserializationError.WithData(
-                        e, d["model"], d.get("pk"), field_value
+                        e, obj["model"], obj.get("pk"), field_value
                     )
-                if value == base.DEFER_FIELD:
-                    deferred_fields[field] = field_value
-                else:
-                    data[field.attname] = value
+
             # Handle all other fields
             else:
                 try:
                     data[field.name] = field.to_python(field_value)
                 except Exception as e:
                     raise base.DeserializationError.WithData(
-                        e, d["model"], d.get("pk"), field_value
+                        e, obj["model"], obj.get("pk"), field_value
                     )
 
-        obj = base.build_instance(Model, data, using)
-        yield base.DeserializedObject(obj, m2m_data, deferred_fields)
+        model_instance = base.build_instance(Model, data, self.using)
+        yield base.DeserializedObject(model_instance, m2m_data, deferred_fields)
 
+    def _handle_m2m_field_node(self, field, field_value):
+        return base.deserialize_m2m_values(
+            field, field_value, self.using, self.handle_forward_references
+        )
 
-def _get_model(model_identifier):
-    """Look up a model from an "app_label.model_name" string."""
-    try:
-        return apps.get_model(model_identifier)
-    except (LookupError, TypeError):
-        raise base.DeserializationError(
-            "Invalid model identifier: '%s'" % model_identifier
+    def _handle_fk_field_node(self, field, field_value):
+        return base.deserialize_fk_value(
+            field, field_value, self.using, self.handle_forward_references
         )
+
+    @staticmethod
+    def _get_model_from_node(model_identifier):
+        """Look up a model from an "app_label.model_name" string."""
+        try:
+            return apps.get_model(model_identifier)
+        except (LookupError, TypeError):
+            raise base.DeserializationError(
+                f"Invalid model identifier: {model_identifier}"
+            )

django/core/serializers/pyyaml.py

@@ -6,7 +6,6 @@
 
 import collections
 import decimal
-from io import StringIO
 
 import yaml
 
@@ -66,17 +65,23 @@ def getvalue(self):
         return super(PythonSerializer, self).getvalue()
 
 
-def Deserializer(stream_or_string, **options):
+class Deserializer(PythonDeserializer):
     """Deserialize a stream or string of YAML data."""
-    if isinstance(stream_or_string, bytes):
-        stream_or_string = stream_or_string.decode()
-    if isinstance(stream_or_string, str):
-        stream = StringIO(stream_or_string)
-    else:
+
+    def __init__(self, stream_or_string, **options):
         stream = stream_or_string
-    try:
-        yield from PythonDeserializer(yaml.load(stream, Loader=SafeLoader), **options)
-    except (GeneratorExit, DeserializationError):
-        raise
-    except Exception as exc:
-        raise DeserializationError() from exc
+        if isinstance(stream_or_string, bytes):
+            stream = stream_or_string.decode()
+        try:
+            objects = yaml.load(stream, Loader=SafeLoader)
+        except Exception as exc:
+            raise DeserializationError() from exc
+        super().__init__(objects, **options)
+
+    def _handle_object(self, obj):
+        try:
+            yield from super()._handle_object(obj)
+        except (GeneratorExit, DeserializationError):
+            raise
+        except Exception as exc:
+            raise DeserializationError(f"Error deserializing object: {exc}") from exc

docs/releases/5.2.txt

@@ -241,7 +241,9 @@ Security
 Serialization
 ~~~~~~~~~~~~~
 
-* ...
+* Each serialization format now defines a ``Deserializer`` class, rather than a
+  function, to improve extensibility when defining a
+  :ref:`custom serialization format <custom-serialization-formats>`.
 
 Signals
 ~~~~~~~