Question

以下是我的简化模型配置：

class Topic(Sortable):
    course = SortableForeignKey(Course)
    publish = models.BooleanField(default=False)
    title = models.CharField(max_length=200)
    text = models.TextField()
    estimated_time = models.PositiveIntegerField(null=True, blank=True))

class Task(models.Model):
    topic = models.ForeignKey(Topic)

class Quiz(Task):
    questions = models.TextField()

    def __unicode__(self):
        return u'[#%s] %s: %s' % (self.id, self.topic.title, capitalize(_("quiz")))

正如您所看到的，有一个主题与Task（非抽象模型）一对多相关。测验是任务继承者之一。我想选择与特定主题相关的所有测验。我只需要测验自己的字段questions及其task_ptr_id - 无需主题数据。以下是我的发言：

Quiz.objects.only('task_ptr_id', 'task_ptr__topic_id', 'questions').filter(topic_id=topic_id)

当我执行它时，执行两个数据库查询：

(0.001) SELECT "website_task"."id", "website_task"."topic_id", "website_quiz"."task_ptr_id", "website_quiz"."questions" FROM "website_quiz" INNER JOIN "website_task" ON ( "website_quiz"."task_ptr_id" = "website_task"."id" ) WHERE "website_task"."topic_id" = 1 LIMIT 21; args=(1,)
(0.000) SELECT "website_topic"."id", "website_topic"."order", "website_topic"."course_id", "website_topic"."publish", "website_topic"."title", "website_topic"."text", "website_topic"."estimated_time" FROM "website_topic" WHERE "website_topic"."id" = 1 LIMIT 21; args=(1,)

如果第一个所需的数据都返回，为什么它会执行第二个？

Answer 1

根据要求，发布作为答案：始终检查您是否未引用其他模型。

Django在不需要时加载父对象

1 个答案: