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.. _jsonify:
JSON Serialization
==================
Pecan includes a simple, easy-to-use system for generating and serving
JSON. To get started, create a file in your project called
``json.py`` and import it in your project's ``app.py``.
Your ``json`` module will contain a series of rules for generating
JSON from objects you return in your controller, utilizing
"generic" function support from the
`simplegeneric <http://pypi.python.org/pypi/simplegeneric>`_ library.
Let's say that we have a controller in our Pecan application which
we want to use to return JSON output for a :class:`User` object::
from myproject.lib import get_current_user
class UsersController(object):
@expose('json')
def current_user(self):
'''
return an instance of myproject.model.User which represents
the current authenticated user
'''
return get_current_user()
In order for this controller to function, Pecan will need to know how to
convert the :class:`User` object into data types compatible with JSON. One
way to tell Pecan how to convert an object into JSON is to define a
rule in your ``json.py``::
from pecan.jsonify import jsonify
from myproject import model
@jsonify.when_type(model.User)
def jsonify_user(user):
return dict(
name = user.name,
email = user.email,
birthday = user.birthday.isoformat()
)
In this example, when an instance of the :class:`model.User` class is
returned from a controller which is configured to return JSON, the
:func:`jsonify_user` rule will be called to convert the object to
JSON-compatible data. Note that the rule does not generate a JSON
string, but rather generates a Python dictionary which contains only
JSON friendly data types.
Alternatively, the rule can be specified on the object itself, by
specifying a :func:`__json__` method in the class::
class User(object):
def __init__(self, name, email, birthday):
self.name = name
self.email = email
self.birthday = birthday
def __json__(self):
return dict(
name = self.name,
email = self.email,
birthday = self.birthday.isoformat()
)
The benefit of using a ``json.py`` module is having all of your JSON
rules defined in a central location, but some projects prefer the
simplicity of keeping the JSON rules attached directly to their
model objects.
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