Django - 应用过滤器时无法访问对象属性

Question

我对 Django 有以下问题：

我的模型定义如下：

from django.db import models

class SettingSection(models.Model):
    section = models.CharField(max_length=20)
    def __unicode__(self):
        return self.section

class SettingParam(models.Model):
    section = models.ForeignKey(SettingSection)
    param = models.CharField(max_length=20, unique=True)
    description = models.CharField(max_length=200, blank=True)
    def __unicode__(self):
        return self.param

class SettingPreset(models.Model):
    preset = models.CharField(max_length=20, unique=True)
    current = models.BooleanField()
    def __unicode__(self):
        return self.preset

class SettingValue(models.Model):
    preset = models.ForeignKey(SettingPreset)
    param = models.ForeignKey(SettingParam)
    value = models.CharField(max_length=100, blank=True)
    def __unicode__(self):
        return self.value

尝试访问我的 SettingValue 对象的任何属性时出现以下错误：

>>> from settings.models import *
>>> preset = SettingPreset.objects.get(current=True)
>>> for section in SettingSection.objects.all():
...     for param in section.settingparam_set.all():
...             v = SettingValue.objects.filter(preset=preset, param=param)
...             print v.id, v.value
... 
Traceback (most recent call last):
  File "<console>", line 4, in <module>
AttributeError: 'QuerySet' object has no attribute 'id'

但是，属性（“id”和“value”）似乎存在：

>>> for section in SettingSection.objects.all():
...     for param in section.settingparam_set.all():
...             v = SettingValue.objects.filter(preset=preset, param=param)
...             print v.values()
... 
[{'value': u'192.168.1.29', 'id': 1, 'preset_id': 1, 'param_id': 1}]
[{'value': u'en1', 'id': 2, 'preset_id': 1, 'param_id': 2}]
[{'value': u'0', 'id': 3, 'preset_id': 1, 'param_id': 3}]
[{'value': u'', 'id': 4, 'preset_id': 1, 'param_id': 4}]
[{'value': u'', 'id': 5, 'preset_id': 1, 'param_id': 5}]

此外，我无需对我的对象应用过滤器即可访问任何属性：

>>> for v in SettingValue.objects.all():
...     print v.id, v.value
... 
1 192.168.1.29
2 en1
3 0
4 
5 

Answer 1

变量 v 是一个查询集，您不能通过查询集访问模型属性。因此，您应该尝试访问查询集中的第一个元素：

for param in section.settingparam_set.all():
    v = SettingValue.objects.filter(preset=preset, param=param)
    print v[0].id, v[0].value #access first element in query set

或者这样做循环你的查询集中的项目：

for param in section.settingparam_set.all():
    v = SettingValue.objects.filter(preset=preset, param=param)
    for item in v:
        print item.id, item.value