Merge pull request #815 from zerok/tickets/11971

Fixed #11971 -- Documented the serialization formats
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Aymeric Augustin 2013-02-24 02:18:32 -08:00
commit b6aede3268
1 changed files with 91 additions and 5 deletions

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@ -162,11 +162,82 @@ Identifier Information
.. _json: http://json.org/
.. _PyYAML: http://www.pyyaml.org/
Notes for specific serialization formats
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
XML
~~~
json
^^^^
The basic XML serialization format is quite simple::
<?xml version="1.0" encoding="utf-8"?>
<django-objects version="1.0">
<object pk="123" model="sessions.session">
<field type="DateTimeField" name="expire_date">2013-01-16T08:16:59.844560+00:00</field>
<!-- ... -->
</object>
</django-objects>
The whole collection of objects that is either serialized or de-serialized is
represented by a ``<django-objects>``-tag which contains multiple
``<object>``-elements. Each such object has two attributes: "pk" and "model",
the latter being represented by the name of the app ("sessions") and the
lowercase name of the model ("session") separated by a dot.
Each field of the object is serialized as a ``<field>``-element sporting the
fields "type" and "name". The text content of the element represents the value
that should be stored.
Foreign keys and other relational fields are treated a little bit differently::
<object pk="27" model="auth.permission">
<!-- ... -->
<field to="contenttypes.contenttype" name="content_type" rel="ManyToOneRel">9</field>
<!-- ... -->
</object>
In this example we specify that the auth.Permission object with the PK 24 has
a foreign key to the contenttypes.ContentType instance with the PK 9.
ManyToMany-relations are exported for the model that binds them. For instance,
the auth.User model has such a relation to the auth.Permission model::
<object pk="1" model="auth.user">
<!-- ... -->
<field to="auth.permission" name="user_permissions" rel="ManyToManyRel">
<object pk="46"></object>
<object pk="47"></object>
</field>
</object>
This example links the given user with the permission models with PKs 46 and 47.
JSON
~~~~
When staying with the same example data as before it would be serialized as
JSON in the following way::
[
{
"pk": "4b678b301dfd8a4e0dad910de3ae245b",
"model": "sessions.session",
"fields": {
"expire_date": "2013-01-16T08:16:59.844Z",
...
}
}
]
The formatting here is a bit simpler than with XML. The whole collection
is just represented as an array and the objects are represented by JSON objects
with three properties: "pk", "model" and "fields". "fields" is again an object
containing each field's name and value as property and property-value
respectively.
Foreign keys just have the PK of the linked object as property value.
ManyToMany-relations are serialized for the model that defines them and are
represented as a list of PKs.
Date and datetime related types are treated in a special way by the JSON
serializer to make the format compatible with `ECMA-262`_.
Be aware that not all Django output can be passed unmodified to :mod:`json`.
In particular, :ref:`lazy translation objects <lazy-translations>` need a
@ -175,14 +246,29 @@ In particular, :ref:`lazy translation objects <lazy-translations>` need a
import json
from django.utils.functional import Promise
from django.utils.encoding import force_text
from django.core.serializers.json import DjangoJSONEncoder
class LazyEncoder(json.JSONEncoder):
class LazyEncoder(DjangoJSONEncoder):
def default(self, obj):
if isinstance(obj, Promise):
return force_text(obj)
return super(LazyEncoder, self).default(obj)
.. _special encoder: http://docs.python.org/library/json.html#encoders-and-decoders
.. _ecma-262: http://www.ecma-international.org/ecma-262/5.1/#sec-15.9.1.15
YAML
~~~~
YAML serialization looks quite similar to JSON. The object list is serialized
as a sequence mappings with the keys "pk", "model" and "fields". Each field is
again a mapping with the key being name of the field and the value the value::
- fields: {expire_date: !!timestamp '2013-01-16 08:16:59.844560+00:00'}
model: sessions.session
pk: 4b678b301dfd8a4e0dad910de3ae245b
Referential fields are again just represented by the PK or sequence of PKs.
.. _topics-serialization-natural-keys: