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