- Author:
- deadwisdom
- Posted:
- August 21, 2007
- Language:
- Python
- Version:
- .96
- Score:
- 8 (after 10 ratings)
This is a great way to pack extra data into a model object, where the structure is dynamic, and not relational. For instance, if you wanted to store a list of dictionaries. The data won't be classically searchable, but you can define pretty much any data construct you'd like, as long as it is JSON-serializable. It's especially useful in a JSON heavy application or one that deals with a lot of javascript.
Example (models.py):
from django.db import models
from jsonfield import JSONField
class Sequence(models.Model):
name = models.CharField(maxlength=25)
list = JSONField()
Example (shell):
fib = Sequence(name='Fibonacci')
fib.list = [0, 1, 1, 2, 3, 5, 8]
fib.save()
fib = Sequence.objects.get(name='Fibonacci')
fib.list.append(13)
print fib.list
[0, 1, 1, 2, 3, 5, 8, 13]
fib.get_list_json()
"[0, 1, 1, 2, 3, 5, 8, 13]"
Note: You can only save JSON-serializable data. Also, dates will be converted to string-timestamps, because I don't really know what better to do with them. Finally, I'm not sure how to interact with forms yet, so that realm is a bit murky.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 | import datetime
from django.db import models
from django.db.models import signals
from django.conf import settings
from django.utils import simplejson as json
from django.dispatch import dispatcher
class JSONEncoder(json.JSONEncoder):
def default(self, obj):
if isinstance(obj, datetime.datetime):
return obj.strftime('%Y-%m-%d %H:%M:%S')
elif isinstance(obj, datetime.date):
return obj.strftime('%Y-%m-%d')
elif isinstance(obj, datetime.time):
return obj.strftime('%H:%M:%S')
return json.JSONEncoder.default(self, obj)
def dumps(data):
return JSONEncoder().encode(data)
def loads(str):
return json.loads(str, encoding=settings.DEFAULT_CHARSET)
class JSONField(models.TextField):
def db_type(self):
return 'text'
def pre_save(self, model_instance, add):
value = getattr(model_instance, self.attname, None)
return dumps(value)
def contribute_to_class(self, cls, name):
super(JSONField, self).contribute_to_class(cls, name)
dispatcher.connect(self.post_init, signal=signals.post_init, sender=cls)
def get_json(model_instance):
return dumps(getattr(model_instance, self.attname, None))
setattr(cls, 'get_%s_json' % self.name, get_json)
def set_json(model_instance, json):
return setattr(model_instance, self.attname, loads(json))
setattr(cls, 'set_%s_json' % self.name, set_json)
def post_init(self, instance=None):
value = self.value_from_object(instance)
if (value):
setattr(instance, self.attname, loads(value))
else:
setattr(instance, self.attname, None)
|
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Comments
In .96 release I had to add
#
This JSONField is really handy, but Django's default JsonSerializer will fail to make valid json string from this field. I ends up to add a "value_to_string" method to JSONField:
However, Django's JsonSerializer does not pick up this method like XmlSerializer does. I have to create my own JsonSerializer like this one:
You need to register this Serializer using "SERIALIZATION_MODULES" in your settings.py.
It works well for me so far.
#
There is another related issue I don't know how to fix. If my model contains a JSONField, management command "loaddata" will fail to load the fixture created by "dumpdata", either in json or xml format.
#
With Django 1.3, this code no longer works
#
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