"""
A custom Model Field for tagging.
"""
from django.db.models import signals
from django.db.models.fields import CharField
from django.utils.translation import ugettext_lazy
from tagging import settings
from tagging.models import Tag
from tagging.utils import edit_string_for_tags
class TagField(CharField):
"""
A "special" character field that actually works as a relationship to tags
"under the hood". This exposes a space-separated string of tags, but does
the splitting/reordering/etc. under the hood.
"""
def __init__(self, *args, **kwargs):
kwargs['max_length'] = kwargs.get('max_length', 255)
kwargs['blank'] = kwargs.get('blank', True)
super(TagField, self).__init__(*args, **kwargs)
def contribute_to_class(self, cls, name):
super(TagField, self).contribute_to_class(cls, name)
# Make this object the descriptor for field access.
setattr(cls, self.name, self)
# Save tags back to the database post-save
signals.post_save.connect(self._save, cls, True)
def __get__(self, instance, owner=None):
"""
Tag getter. Returns an instance's tags if accessed on an instance, and
all of a model's tags if called on a class. That is, this model::
class Link(models.Model):
...
tags = TagField()
Lets you do both of these::
>>> l = Link.objects.get(...)
>>> l.tags
'tag1 tag2 tag3'
>>> Link.tags
'tag1 tag2 tag3 tag4'
"""
# Handle access on the model (i.e. Link.tags)
if instance is None:
return edit_string_for_tags(Tag.objects.usage_for_model(owner))
tags = self._get_instance_tag_cache(instance)
if tags is None:
if instance.pk is None:
self._set_instance_tag_cache(instance, '')
else:
self._set_instance_tag_cache(
instance, edit_string_for_tags(Tag.objects.get_for_object(instance)))
return self._get_instance_tag_cache(instance)
def __set__(self, instance, value):
"""
Set an object's tags.
"""
if instance is None:
raise AttributeError(_('%s can only be set on instances.') % self.name)
if settings.FORCE_LOWERCASE_TAGS and value is not None:
value = value.lower()
self._set_instance_tag_cache(instance, value)
def _save(self, **kwargs): #signal, sender, instance):
"""
Save tags back to the database
"""
tags = self._get_instance_tag_cache(kwargs['instance'])
if tags is not None:
Tag.objects.update_tags(kwargs['instance'], tags)
def __delete__(self, instance):
"""
Clear all of an object's tags.
"""
self._set_instance_tag_cache(instance, '')
def _get_instance_tag_cache(self, instance):
"""
Helper: get an instance's tag cache.
"""
return getattr(instance, '_%s_cache' % self.attname, None)
def _set_instance_tag_cache(self, instance, tags):
"""
Helper: set an instance's tag cache.
"""
setattr(instance, '_%s_cache' % self.attname, tags)
def get_internal_type(self):
return 'CharField'
def formfield(self, **kwargs):
from tagging import forms
defaults = {'form_class': forms.TagField}
defaults.update(kwargs)
return super(TagField, self).formfield(**defaults)
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