我的模型之一具有未存储在数据库中的属性。视图和模型级别的一切都很好,但我似乎无法在模板中显示这些“非数据库”属性。使Django模型中的瞬态(非数据库)属性可用于模板
下面是一些示例代码,这是一个反映实际问题域的仿真示例,用于演示不良行为。
的观点:
def odometer(request):
cars = Car.objects.all()
for car in cars:
car.read_meters()
context = {'cars': cars}
return render_to_response('odometer.html', context)
的车型:
class Car(models.Model):
name = models.CharField(_('name'), max_length=100, unique=True)
def read_meters(self):
for meter in self.meter_set.all():
meter.read()
def __unicode__(self):
return '%s' % self.name
class Meter(models.Model):
name = models.CharField(_('name'), max_length=100)
car = models.ForeignKey(Car)
difference = 0
previous = 0
changed = False
def read(self):
# this is completely artificial. in the real application we would interface with the hardware
# meter to get data
try:
previous_count = MeterReading.objects.filter(meter__id=self.id).order_by('-stamp')[0].count
except:
previous_count = 0
self.previous = previous_count
current_count = previous_count
if (random.randrange(0, 2) == 0):
self.difference = int(random.random() * 100)
if self.name == 'Odometer' or (random.randrange(0, 2) == 0):
current_count += self.difference
else:
current_count -= self.difference
if current_count < 0:
current_count = 0
if current_count > previous_count:
self.changed = True
new_reading = MeterReading()
new_reading.count = current_count
new_reading.meter = self
new_reading.save()
def __unicode__(self):
return '%s' % self.name
class MeterReading(models.Model):
count = models.IntegerField(_('count'))
stamp = models.DateTimeField(editable=False, auto_now_add=True)
meter = models.ForeignKey(Meter)
def __unicode__(self):
return '%s' % self.count
而且模板:
{% for car in cars %}
<h2>{{ car }}</h2>
{% for meter in car.meter_set.all %}
<h3>{{ meter }}</h3>
<p>Difference: {{ meter.difference }}</p>
<p>Changed: {{ meter.changed }}</p>
<ul>
{% for reading in meter.meterreading_set.all %}
<li>{{ reading }}</li>
{% endfor %}
</ul>
{% endfor %}
{% endfor %}
的问题是 'meter.difference' 和 'meter.changed' 唐输出正确的更新值。我究竟做错了什么?任何建议表示赞赏。
谢谢。
汽车模型:
class Car(models.Model):
name = models.CharField(_('name'), max_length=100, unique=True)
def read_meters(self):
for meter in self.meters:
meter.read()
def __unicode__(self):
return '%s' % self.name
@property
def meters(self):
if not hasattr(self, '_meters'):
self._meters = self.meter_set.all()
return self._meters
而且模板:
{% for car in cars %}
<h2>{{ car }}</h2>
{% for meter in car.meters %}
<h3>{{ meter }}</h3>
<p>{{ meter.name }} difference: {{ meter.difference }}</p>
<p>Changed: {{ meter.changed }}</p>
<ul>
{% for reading in meter.meterreading_set.all %}
<li>{{ reading }}</li>
{% endfor %}
</ul>
{% endfor %}
{% endfor %}
真棒谢谢你。 – 2009-11-13 13:36:57