source: djangobb_forum/fields.py @ 434:21cb6ef7649d

"""
Details about AutoOneToOneField:
    http://softwaremaniacs.org/blog/2007/03/07/auto-one-to-one-field/
"""
try:
    from cStringIO import StringIO
except ImportError:
    from StringIO import StringIO
import random
from hashlib import sha1

from django.db.models import OneToOneField
from django.db.models.fields.related import SingleRelatedObjectDescriptor 
from django.db import models
from django.core.files.uploadedfile import SimpleUploadedFile
from django.core.serializers.json import DjangoJSONEncoder
from django.utils import simplejson as json
from django.conf import settings


class AutoSingleRelatedObjectDescriptor(SingleRelatedObjectDescriptor):
    def __get__(self, instance, instance_type=None):
        try:
            return super(AutoSingleRelatedObjectDescriptor, self).__get__(instance, instance_type)
        except self.related.model.DoesNotExist:
            obj = self.related.model(**{self.related.field.name: instance})
            obj.save()
            return obj


class AutoOneToOneField(OneToOneField):
    """
    OneToOneField creates dependent object on first request from parent object
    if dependent oject has not created yet.
    """

    def contribute_to_related_class(self, cls, related):
        setattr(cls, related.get_accessor_name(), AutoSingleRelatedObjectDescriptor(related))
        #if not cls._meta.one_to_one_field:
        #    cls._meta.one_to_one_field = self


class ExtendedImageField(models.ImageField):
    """
    Extended ImageField that can resize image before saving it.
    """

    def __init__(self, *args, **kwargs):
        self.width = kwargs.pop('width', None)
        self.height = kwargs.pop('height', None)
        super(ExtendedImageField, self).__init__(*args, **kwargs)

    def save_form_data(self, instance, data):
        if data and self.width and self.height:
            content = self.resize_image(data.read(), width=self.width, height=self.height)
            salt = sha1(str(random.random())).hexdigest()[:5]
            fname =  sha1(salt + settings.SECRET_KEY).hexdigest() + '.png'
            data = SimpleUploadedFile(fname, content, data.content_type)
        super(ExtendedImageField, self).save_form_data(instance, data)

    def resize_image(self, rawdata, width, height):
        """
        Resize image to fit it into (width, height) box.
        """
        try:
            import Image
        except ImportError:
            from PIL import Image
        image = Image.open(StringIO(rawdata))
        oldw, oldh = image.size
        if oldw >= oldh:
            x = int(round((oldw - oldh) / 2.0))
            image = image.crop((x, 0, (x + oldh) - 1, oldh - 1))
        else:
            y = int(round((oldh - oldw) / 2.0))
            image = image.crop((0, y, oldw - 1, (y + oldw) - 1))
        image = image.resize((width, height), resample=Image.ANTIALIAS)


        string = StringIO()
        image.save(string, format='PNG')
        return string.getvalue()


class JSONField(models.TextField):
    """
    JSONField is a generic textfield that neatly serializes/unserializes
    JSON objects seamlessly.
    Django snippet #1478
    """

    __metaclass__ = models.SubfieldBase

    def to_python(self, value):
        if value == "":
            return None

        try:
            if isinstance(value, basestring):
                return json.loads(value)
        except ValueError:
            pass
        return value

    def get_prep_value(self, value):
        if value == "":
            return None
        if isinstance(value, dict):
            value = json.dumps(value, cls=DjangoJSONEncoder)
        return super(JSONField, self).get_prep_value(value)