--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/web/lib/tagging/fields.py	Fri Jan 22 18:23:34 2010 +0100
@@ -0,0 +1,107 @@
+"""
+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 as _
+
+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)