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103 lines
3.7 KiB
Plaintext
103 lines
3.7 KiB
Plaintext
==========================
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Serializing Django objects
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==========================
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.. note::
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This API is currently under heavy development and may change --
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perhaps drastically -- in the future.
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You have been warned.
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Django's serialization framework provides a mechanism for "translating" Django
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objects into other formats. Usually these other formats will be text-based and
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used for sending Django objects over a wire, but it's possible for a
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serializer to handle any format (text-based or not).
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Serializing data
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----------------
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At the highest level, serializing data is a very simple operation::
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from django.core import serializers
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data = serializers.serialize("xml", SomeModel.objects.all())
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The arguments to the ``serialize`` function are the format to serialize the
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data to (see `Serialization formats`_) and a QuerySet_ to serialize.
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(Actually, the second argument can be any iterator that yields Django objects,
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but it'll almost always be a QuerySet).
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.. _QuerySet: ../db_api/#retrieving-objects
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You can also use a serializer object directly::
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xml_serializer = serializers.get_serializer("xml")
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xml_serializer.serialize(queryset)
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data = xml_serializer.getvalue()
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This is useful if you want to serialize data directly to a file-like object
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(which includes a HTTPResponse_)::
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out = open("file.xml", "w")
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xml_serializer.serialize(SomeModel.objects.all(), stream=out)
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.. _HTTPResponse: ../request_response/#httpresponse-objects
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Deserializing data
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------------------
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Deserializing data is also a fairly simple operation::
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for obj in serializers.deserialize("xml", data):
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do_something_with(obj)
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As you can see, the ``deserialize`` function takes the same format argument as
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``serialize``, a string or stream of data, and returns an iterator.
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However, here it gets slightly complicated. The objects returned by the
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``deserialize`` iterator *aren't* simple Django objects. Instead, they are
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special ``DeserializedObject`` instances that wrap a created -- but unsaved --
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object and any associated relationship data.
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Calling ``DeserializedObject.save()`` saves the object to the database.
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This ensures that deserializing is a non-destructive operation even if the
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data in your serialized representation doesn't match what's currently in the
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database. Usually, working with these ``DeserializedObject`` instances looks
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something like::
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for deserialized_object in serializers.deserialize("xml", data):
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if object_should_be_saved(deserialized_object):
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obj.save()
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In other words, the usual use is to examine the deserialized objects to make
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sure that they are "appropriate" for saving before doing so. Of course, if you trust your data source you could just save the object and move on.
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The Django object itself can be inspected as ``deserialized_object.object``.
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Serialization formats
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---------------------
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Django "ships" with a few included serializers:
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========== ==============================================================
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Identifier Information
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========== ==============================================================
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``xml`` Serializes to and from a simple XML dialect.
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``json`` Serializes to and from JSON_ (using a version of simplejson_
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bundled with Django).
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``python`` Translates to and from "simple" Python objects (lists, dicts,
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strings, etc.). Not really all that useful on its own, but
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used as a base for other serializers.
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========== ==============================================================
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.. _json: http://json.org/
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.. _simplejson: http://undefined.org/python/#simplejson
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Writing custom serializers
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``````````````````````````
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XXX ...
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