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from __future__ import unicode_literals
from django.db import models
from django.utils.translation import ugettext_lazy as _
from django.db.models.fields import FieldDoesNotExist
from django.core.exceptions import ImproperlyConfigured
from django.utils.timezone import now
from model_utils.managers import QueryManager
from model_utils.fields import AutoCreatedField, AutoLastModifiedField, \
StatusField, MonitorField
class TimeStampedModel(models.Model):
"""
An abstract base class model that provides self-updating
``created`` and ``modified`` fields.
"""
created = AutoCreatedField(_('created'))
modified = AutoLastModifiedField(_('modified'))
class Meta:
abstract = True
class TimeFramedModel(models.Model):
"""
An abstract base class model that provides ``start``
and ``end`` fields to record a timeframe.
"""
start = models.DateTimeField(_('start'), null=True, blank=True)
end = models.DateTimeField(_('end'), null=True, blank=True)
class Meta:
abstract = True
class StatusModel(models.Model):
"""
An abstract base class model with a ``status`` field that
automatically uses a ``STATUS`` class attribute of choices, a
``status_changed`` date-time field that records when ``status``
was last modified, and an automatically-added manager for each
status that returns objects with that status only.
"""
status = StatusField(_('status'))
status_changed = MonitorField(_('status changed'), monitor='status')
class Meta:
abstract = True
def add_status_query_managers(sender, **kwargs):
"""
Add a Querymanager for each status item dynamically.
"""
if not issubclass(sender, StatusModel):
return
for value, display in getattr(sender, 'STATUS', ()):
if _field_exists(sender, value):
raise ImproperlyConfigured(
"StatusModel: Model '%s' has a field named '%s' which "
"conflicts with a status of the same name."
% (sender.__name__, value)
)
sender.add_to_class(value, QueryManager(status=value))
def add_timeframed_query_manager(sender, **kwargs):
"""
Add a QueryManager for a specific timeframe.
"""
if not issubclass(sender, TimeFramedModel):
return
if _field_exists(sender, 'timeframed'):
raise ImproperlyConfigured(
"Model '%s' has a field named 'timeframed' "
"which conflicts with the TimeFramedModel manager."
% sender.__name__
)
sender.add_to_class('timeframed', QueryManager(
(models.Q(start__lte=now) | models.Q(start__isnull=True)) &
(models.Q(end__gte=now) | models.Q(end__isnull=True))
))
models.signals.class_prepared.connect(add_status_query_managers)
models.signals.class_prepared.connect(add_timeframed_query_manager)
def _field_exists(model_class, field_name):
return field_name in [f.attname for f in model_class._meta.local_fields]
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