在Django注解中可以对关联项进行过滤吗？

Question

我有以下两个模型：

class Job(models.Model):
    title = models.CharField(_('title'), max_length=50)
    description = models.TextField(_('description'))
    category = models.ForeignKey(JobCategory, related_name='jobs')
    created_date = models.DateTimeField(auto_now_add=True)

class JobCategory(models.Model):
    title = models.CharField(_('title'), max_length=50)
    slug = models.SlugField(_('slug'))

到目前为止，我的查询进展是这样的：

def job_categories():
    categories = JobCategory.objects.annotate(num_postings=Count('jobs'))
    return {'categories': categories}

问题是我只想统计过去30天内创建的工作。我想返回所有类别，而不仅仅是那些有符合条件工作的类别。

Answer 1

这只是个猜测……这样做会有效吗？

def job_categories():
    thritydaysago = datetime.datetime.now() - datetime.timedelta(days=30)
    categories = JobCategory.objects.filter(job__created_date__gte=thritydaysago).annotate(num_postings=Count('jobs'))
    return {'categories': categories}

想了解更多关于跨关系查询的内容，可以查看这个链接："跨关系查找"。嗯……可能还需要再加一个查询来获取所有的分类……

Answer 2

我决定换个方式来处理这个问题，干脆不使用注解。我在工作模型（Job model）里添加了一个管理器，这个管理器只返回最近30天内的活跃工作。然后我在工作类别模型（JobCategory model）上创建了一个属性，用来查询这个类别下的工作数量。我的模板标签（templatetag）只是简单地返回所有的类别。下面是相关的代码。

class JobCategory(models.Model):
    title = models.CharField(_('title'), max_length=50, help_text=_("Max 50 chars. Required."))
    slug = models.SlugField(_('slug'), help_text=_("Only letters, numbers, or hyphens. Required."))

    class Meta:
        verbose_name = _('job category')
        verbose_name_plural = _('job categories')

    def __unicode__(self):
        return self.title

    def get_absolute_url(self):
        return reverse('djobs_category_jobs', args=[self.slug])

    @property
    def active_job_count(self):
        return len(Job.active.filter(category=self))

class ActiveJobManager(models.Manager):
    def get_query_set(self):
        return super(ActiveJobManager, self).get_query_set().filter(created_date__gte=datetime.datetime.now() - datetime.timedelta(days=30))

class Job(models.Model):
    title = models.CharField(_('title'), max_length=50, help_text=_("Max 50 chars. Required."))
    description = models.TextField(_('description'), help_text=_("Required."))
    category = models.ForeignKey(JobCategory, related_name='jobs')
    employment_type = models.CharField(_('employment type'), max_length=5, choices=EMPLOYMENT_TYPE_CHOICES, help_text=_("Required."))
    employment_level = models.CharField(_('employment level'), max_length=5, choices=EMPLOYMENT_LEVEL_CHOICES, help_text=_("Required."))
    employer = models.ForeignKey(Employer)
    location = models.ForeignKey(Location)
    contact = models.ForeignKey(Contact)
    allow_applications = models.BooleanField(_('allow applications'))
    created_date = models.DateTimeField(auto_now_add=True)

    objects = models.Manager()
    active = ActiveJobManager()

    class Meta:
        verbose_name = _('job')
        verbose_name_plural = _('jobs')

    def __unicode__(self):
        return '%s at %s' % (self.title, self.employer.name)

还有这个标签...

def job_categories():
    categories = JobCategory.objects.all()
    return {'categories': categories}