django/core/serializers/__init__.py
"""
Interfaces for serializing Django objects.
Usage::
from django.core import serializers
json = serializers.serialize("json", some_queryset)
objects = list(serializers.deserialize("json", json))
To add your own serializers, use the SERIALIZATION_MODULES setting::
SERIALIZATION_MODULES = {
"csv": "path.to.csv.serializer",
"txt": "path.to.txt.serializer",
}
"""
import importlib
from django.apps import apps
from django.conf import settings
from django.core.serializers.base import SerializerDoesNotExist
# Built-in serializers
BUILTIN_SERIALIZERS = {
"xml": "django.core.serializers.xml_serializer",
"python": "django.core.serializers.python",
"json": "django.core.serializers.json",
"yaml": "django.core.serializers.pyyaml",
"jsonl": "django.core.serializers.jsonl",
}
_serializers = {}
class BadSerializer:
"""
Stub serializer to hold exception raised during registration
This allows the serializer registration to cache serializers and if there
is an error raised in the process of creating a serializer it will be
raised and passed along to the caller when the serializer is used.
"""
internal_use_only = False
def __init__(self, exception):
self.exception = exception
def __call__(self, *args, **kwargs):
raise self.exception
def register_serializer(format, serializer_module, serializers=None):
"""Register a new serializer.
``serializer_module`` should be the fully qualified module name
for the serializer.
If ``serializers`` is provided, the registration will be added
to the provided dictionary.
If ``serializers`` is not provided, the registration will be made
directly into the global register of serializers. Adding serializers
directly is not a thread-safe operation.
"""
if serializers is None and not _serializers:
_load_serializers()
try:
module = importlib.import_module(serializer_module)
except ImportError as exc:
bad_serializer = BadSerializer(exc)
module = type(
"BadSerializerModule",
(),
{
"Deserializer": bad_serializer,
"Serializer": bad_serializer,
},
)
if serializers is None:
_serializers[format] = module
else:
serializers[format] = module
def unregister_serializer(format):
"Unregister a given serializer. This is not a thread-safe operation."
if not _serializers:
_load_serializers()
if format not in _serializers:
raise SerializerDoesNotExist(format)
del _serializers[format]
def get_serializer(format):
if not _serializers:
_load_serializers()
if format not in _serializers:
raise SerializerDoesNotExist(format)
return _serializers[format].Serializer
def get_serializer_formats():
if not _serializers:
_load_serializers()
return list(_serializers)
def get_public_serializer_formats():
if not _serializers:
_load_serializers()
return [k for k, v in _serializers.items() if not v.Serializer.internal_use_only]
def get_deserializer(format):
if not _serializers:
_load_serializers()
if format not in _serializers:
raise SerializerDoesNotExist(format)
return _serializers[format].Deserializer
def serialize(format, queryset, **options):
"""
Serialize a queryset (or any iterator that returns database objects) using
a certain serializer.
"""
s = get_serializer(format)()
s.serialize(queryset, **options)
return s.getvalue()
def deserialize(format, stream_or_string, **options):
"""
Deserialize a stream or a string. Return an iterator that yields ``(obj,
m2m_relation_dict)``, where ``obj`` is an instantiated -- but *unsaved* --
object, and ``m2m_relation_dict`` is a dictionary of ``{m2m_field_name :
list_of_related_objects}``.
"""
d = get_deserializer(format)
return d(stream_or_string, **options)
def _load_serializers():
"""
Register built-in and settings-defined serializers. This is done lazily so
that user code has a chance to (e.g.) set up custom settings without
needing to be careful of import order.
"""
global _serializers
serializers = {}
for format in BUILTIN_SERIALIZERS:
register_serializer(format, BUILTIN_SERIALIZERS[format], serializers)
if hasattr(settings, "SERIALIZATION_MODULES"):
for format in settings.SERIALIZATION_MODULES:
register_serializer(
format, settings.SERIALIZATION_MODULES[format], serializers
)
_serializers = serializers
def sort_dependencies(app_list, allow_cycles=False):
"""Sort a list of (app_config, models) pairs into a single list of models.
The single list of models is sorted so that any model with a natural key
is serialized before a normal model, and any model with a natural key
dependency has it's dependencies serialized first.
If allow_cycles is True, return the best-effort ordering that will respect
most of dependencies but ignore some of them to break the cycles.
"""
# Process the list of models, and get the list of dependencies
model_dependencies = []
models = set()
for app_config, model_list in app_list:
if model_list is None:
model_list = app_config.get_models()
for model in model_list:
models.add(model)
# Add any explicitly defined dependencies
if hasattr(model, "natural_key"):
deps = getattr(model.natural_key, "dependencies", [])
if deps:
deps = [apps.get_model(dep) for dep in deps]
else:
deps = []
# Now add a dependency for any FK relation with a model that
# defines a natural key
for field in model._meta.fields:
if field.remote_field:
rel_model = field.remote_field.model
if hasattr(rel_model, "natural_key") and rel_model != model:
deps.append(rel_model)
# Also add a dependency for any simple M2M relation with a model
# that defines a natural key. M2M relations with explicit through
# models don't count as dependencies.
for field in model._meta.many_to_many:
if field.remote_field.through._meta.auto_created:
rel_model = field.remote_field.model
if hasattr(rel_model, "natural_key") and rel_model != model:
deps.append(rel_model)
model_dependencies.append((model, deps))
model_dependencies.reverse()
# Now sort the models to ensure that dependencies are met. This
# is done by repeatedly iterating over the input list of models.
# If all the dependencies of a given model are in the final list,
# that model is promoted to the end of the final list. This process
# continues until the input list is empty, or we do a full iteration
# over the input models without promoting a model to the final list.
# If we do a full iteration without a promotion, that means there are
# circular dependencies in the list.
model_list = []
while model_dependencies:
skipped = []
changed = False
while model_dependencies:
model, deps = model_dependencies.pop()
# If all of the models in the dependency list are either already
# on the final model list, or not on the original serialization list,
# then we've found another model with all it's dependencies satisfied.
if all(d not in models or d in model_list for d in deps):
model_list.append(model)
changed = True
else:
skipped.append((model, deps))
if not changed:
if allow_cycles:
# If cycles are allowed, add the last skipped model and ignore
# its dependencies. This could be improved by some graph
# analysis to ignore as few dependencies as possible.
model, _ = skipped.pop()
model_list.append(model)
else:
raise RuntimeError(
"Can't resolve dependencies for %s in serialized app list."
% ", ".join(
model._meta.label
for model, deps in sorted(
skipped, key=lambda obj: obj[0].__name__
)
),
)
model_dependencies = skipped
return model_list