django中如何实现model对象加入装饰器

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＃在现有的对象加入日期修改Mixin

class Person(CreationModificationDateMixin):

多出字段：

＃加入url MinIn

class Person(UrlMixin):

＃加入原数据MInxIn

class Person(MetaTagsMixin):

多出字段：

# -*- coding: UTF-8 -*-from __future__ import unicode_literalsimport urlparsefrom django.conf import settingsfrom django.utils.timezone import now as timezone_nowfrom django.utils.safestring import mark_safefrom django.template.defaultfilters import escapefrom django.db import modelsfrom django.utils.translation import ugettext_lazy as _from django.contrib.contenttypes.models import ContentTypefrom django.contrib.contenttypes.fields import GenericForeignKeyfrom django.core.exceptions import FieldError### See recipe "Model mixin with URL-related methods"class UrlMixin(models.Model):    """    A replacement for get_absolute_url()    Models extending this mixin should have either get_url or get_url_path implemented.    http://code.djangoproject.com/wiki/ReplacingGetAbsoluteUrl    """    class Meta:        abstract = True    def get_url(self):        if hasattr(self.get_url_path, "dont_recurse"):            raise NotImplementedError        try:            path = self.get_url_path()        except NotImplementedError:            raise        website_url = getattr(settings, "DEFAULT_WEBSITE_URL", "http://127.0.0.1:8000")        return website_url + path    get_url.dont_recurse = True    def get_url_path(self):        if hasattr(self.get_url, "dont_recurse"):            raise NotImplementedError        try:            url = self.get_url()        except NotImplementedError:            raise        bits = urlparse.urlparse(url)        return urlparse.urlunparse(("", "") + bits[2:])    get_url_path.dont_recurse = True    def get_absolute_url(self):        return self.get_url_path()### See recipe "Model mixin handling creation and modification dates"class CreationModificationDateMixin(models.Model):    """    Abstract base class with a creation and modification date and time    """    created = models.DateTimeField(        _("creation date and time"),        editable=False,    )    modified = models.DateTimeField(        _("modification date and time"),        null=True,        editable=False,    )    def save(self, *args, **kwargs):        if not self.pk:            self.created = timezone_now()        else:            # To ensure that we have a creation data always, we add this one            if not self.created:                self.created = timezone_now()            self.modified = timezone_now()        super(CreationModificationDateMixin, self).save(*args, **kwargs)    save.alters_data = True    class Meta:        abstract = True### See recipe "Model mixin taking care of meta tags"class MetaTagsMixin(models.Model):    """    Abstract base class for meta tags in the  section    """    meta_keywords = models.CharField(        _("Keywords"),        max_length=255,        blank=True,        help_text=_("Separate keywords by comma."),    )    meta_description = models.CharField(        _("Description"),        max_length=255,        blank=True,    )    meta_author = models.CharField(        _("Author"),        max_length=255,        blank=True,    )    meta_copyright = models.CharField(        _("Copyright"),        max_length=255,        blank=True,    )    class Meta:        abstract = True    def get_meta_keywords(self):        meta_tag = ""        if self.meta_keywords:            meta_tag = """\n""" % escape(self.meta_keywords)        return mark_safe(meta_tag)    def get_meta_description(self):        meta_tag = ""        if self.meta_description:            meta_tag = """\n""" % escape(self.meta_description)        return mark_safe(meta_tag)    def get_meta_author(self):        meta_tag = ""        if self.meta_author:            meta_tag = """\n""" % escape(self.meta_author)        return mark_safe(meta_tag)    def get_meta_copyright(self):        meta_tag = ""        if self.meta_copyright:            meta_tag = """\n""" % escape(self.meta_copyright)        return mark_safe(meta_tag)    def get_meta_tags(self):        return mark_safe("".join((            self.get_meta_keywords(),            self.get_meta_description(),            self.get_meta_author(),            self.get_meta_copyright(),        )))### See recipe "Model mixin handling generic relations"def object_relation_mixin_factory(        prefix=None,        prefix_verbose=None,        add_related_name=False,        limit_content_type_choices_to={},        limit_object_choices_to={},        is_required=False,    ):    """    returns a mixin class for generic foreign keys using    "Content type - object Id" with dynamic field names.    This function is just a class generator    Parameters:    prefix : a prefix, which is added in front of the fields    prefix_verbose :    a verbose name of the prefix, used to                        generate a title for the field column                        of the content object in the Admin.    add_related_name :  a boolean value indicating, that a                        related name for the generated content                        type foreign key should be added. This                        value should be true, if you use more                        than one ObjectRelationMixin in your model.    The model fields are created like this:    <>_content_type :   Field name for the "content type"    <>_object_id :      Field name for the "object Id"    <>_content_object : Field name for the "content object"    """    p = ""    if prefix:        p = "%s_" % prefix    content_type_field = "%scontent_type" % p    object_id_field = "%sobject_id" % p    content_object_field = "%scontent_object" % p    class TheClass(models.Model):        class Meta:            abstract = True    if add_related_name:        if not prefix:            raise FieldError("if add_related_name is set to True, a prefix must be given")        related_name = prefix    else:        related_name = None    optional = not is_required    ct_verbose_name = (        _("%s's type (model)") % prefix_verbose        if prefix_verbose        else _("Related object's type (model)")    )    content_type = models.ForeignKey(        ContentType,        verbose_name=ct_verbose_name,        related_name=related_name,        blank=optional,        null=optional,        help_text=_("Please select the type (model) for the relation, you want to build."),        limit_choices_to=limit_content_type_choices_to,    )    fk_verbose_name = (prefix_verbose or _("Related object"))    object_id = models.CharField(        fk_verbose_name,        blank=optional,        null=False,        help_text=_("Please enter the ID of the related object."),        max_length=255,        default="",  # for south migrations    )    object_id.limit_choices_to = limit_object_choices_to    # can be retrieved by MyModel._meta.get_field("object_id").limit_choices_to    content_object = GenericForeignKey(        ct_field=content_type_field,        fk_field=object_id_field,    )    TheClass.add_to_class(content_type_field, content_type)    TheClass.add_to_class(object_id_field, object_id)    TheClass.add_to_class(content_object_field, content_object)    return TheClass

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