我已经通过其他多个职位,所以这一个似乎是重复,但我找不到答案。我是新来的,所以我很抱歉,如果这不是正确的方式进行。你知道吗
我用的是Django 2.2
根据官方文档,select\u related()返回一个QuerySet,它将“跟踪”外键关系,在执行查询时选择其他相关对象数据:https://docs.djangoproject.com/en/2.2/ref/models/querysets/#select-related
以下是官方示例: 您可以使用与查询外键类似的方式来跟踪外键。如果您有以下型号:
from django.db import models
class City(models.Model):
# ...
pass
class Person(models.Model):
# ...
hometown = models.ForeignKey(
City,
on_delete=models.SET_NULL,
blank=True,
null=True,
)
class Book(models.Model):
# ...
author = models.ForeignKey(Person, on_delete=models.CASCADE)
然后打电话给Book.objects.select\相关('author\u homerium').get(id=4)将缓存相关人员和相关城市:
# Hits the database with joins to the author and hometown tables.
b = Book.objects.select_related('author__hometown').get(id=4)
p = b.author # Doesn't hit the database.
c = p.hometown # Doesn't hit the database.
# Without select_related()...
b = Book.objects.get(id=4) # Hits the database.
p = b.author # Hits the database.
c = p.hometown # Hits the database.
这是我的密码:
class Campaign(SlugifyNameMixin, TimeStampedModel, TimeFramedModel,
StatusModel):
STATUS = Choices(
('draft', _('Draft')),
('published', _('Published')),
('disabled', _('Disabled')),
)
banner = ThumbnailerImageField(verbose_name=_('Banner'),
help_text=_('Choose a representative banner image'),
upload_to='campaigns/banners/',
blank=True
)
tagline = models.CharField(max_length=150, verbose_name=_('Tagline'), help_text=_('A short campaign description'))
organization = models.ForeignKey(Organization,
on_delete=models.PROTECT,
related_name='campaigns',
verbose_name=_('Organization'),
help_text=_('Select the organization that this campaign belongs to.')
)
description = RichTextUploadingField(null=False, default='',
verbose_name=_('Description'),
help_text=_('A description of this campaign and what it aims to accomplish')
)
class Meta:
verbose_name = _("Campaign")
verbose_name_plural = _("Campaigns")
unique_together = ("organization", "slug")
permissions = (('change_campaign_status', 'Can change the status of campaigns'),)
def __str__(self):
return '%s' % (self.name)
def get_absolute_url(self):
return reverse('explore:campaign-detail', args=[self.organization.slug, self.slug])
class Action(SlugifyNameMixin, TimeStampedModel):
campaign = models.ForeignKey(Campaign,
on_delete=models.PROTECT,
related_name='actions',
verbose_name=_('campaign'),
help_text=_('Select the campaign that this action belongs to.')
)
class Meta:
verbose_name = _('Action')
verbose_name_plural = _('Actions')
permissions = (('change_action_status', 'Can change the status of actions'),)
def __str__(self):
return '%s' % (self.name)
class ActionMeta(TimeStampedModel, StatusModel):
STATUS = Choices(
('open', _('Open')),
('in-progress', _('In-Progress')),
('completed', _('Completed')),
)
user = models.ForeignKey(settings.AUTH_USER_MODEL, verbose_name=_('user'), on_delete=models.PROTECT)
action = models.ForeignKey(Action, on_delete=models.CASCADE, related_name='metas', verbose_name=_('action'))
class Meta:
verbose_name = _('Action Meta')
verbose_name_plural = _('Action Metas')
unique_together = ('user', 'action')
def __str__(self):
return '%s-meta-%s' % (self.action.name, self.id)
我的问题是我无法检索活动对象
>>> camp11 = Campaign.objects.get(name='camp11')
>>> camp12 = Campaign.objects.get(name='camp12')
>>> action11u1 = Action.objects.get(name='action11u1')
>>> action12u1 = Action.objects.get(name='action12u1')
>>> am1 = ActionMeta.objects.create(user=u, action=action11u1)
>>> am2 = ActionMeta.objects.create(user=u, action=action12u1)
>>> a1 = ActionMeta.objects.select_related('action__campaign').get(pk=am1.pk)
>>> a1.campaign
Traceback (most recent call last):
File "<console>", line 1, in <module>
AttributeError: 'ActionMeta' object has no attribute 'campaign'
>>> a1.action
<Action: action11u1>
这里是数据库查询
>>> print(a1.query)
SELECT "core_actionmeta"."id", "core_actionmeta"."created", "core_actionmeta"."modified", "core_actionmeta"."status", "core_actionmeta"."status_changed", "core_actionmeta"."user_id", "core_actionmeta"."action_id", "core_action"."id", "core_action"."created", "core_action"."modified", "core_action"."name", "core_action"."slug", "core_action"."campaign_id", "core_campaign"."id", "core_campaign"."created", "core_campaign"."modified", "core_campaign"."start", "core_campaign"."end", "core_campaign"."status", "core_campaign"."status_changed", "core_campaign"."name", "core_campaign"."name_en", "core_campaign"."name_fa", "core_campaign"."slug", "core_campaign"."banner", "core_campaign"."tagline", "core_campaign"."tagline_en", "core_campaign"."tagline_fa", "core_campaign"."organization_id", "core_campaign"."description", "core_campaign"."description_en", "core_campaign"."description_fa" FROM "core_actionmeta" INNER JOIN "core_action" ON ("core_actionmeta"."action_id" = "core_action"."id") INNER JOIN "core_campaign" ON ("core_action"."campaign_id" = "core_campaign"."id") WHERE "core_actionmeta"."id" = 3
你仍然需要通过
action
。尝试:旁注:我可能会更改
ActionMeta
的名称,因为Meta
有这样一个特定的含义,而且已经有了Action.Meta
。你知道吗相关问题 更多 >
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