Django干货知识分享，ORM模型(三)（django orm源码解析）

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一对多关系

使用ForeignKey，创建用户表和文章表结构

class User(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)

    def __str__(self) -> str:
        return '{0} {1}'.format(self.first_name, self.last_name)

class Article(models.Model):
    title = models.CharField(max_length=100)
    add_date = models.DateField(auto_now_add=True)
    user = models.ForeignKey(User, on_delete=models.CASCADE)

    def __str__(self) -> str:
        return self.title

新增数据

>>> from myproject.myapp.models import User, Article
>>> user1 = User(first_name='小', last_name='华')
>>> user1.save
<bound method Model.save of <User: 小 华>>
>>> user2 = User(first_name='小', last_name='米')
>>> user2.save()
>>> user1.save()
>>> a1 = Article(title='小华写了第一篇文章', user=user1)
>>> a1.save()
>>> a2 = Article(title='小华写了第二篇文章', user=user1)
>>> a2.save()
>>> a3 = Article(title='小米写了第一篇文章', user=user2)
>>> a3.save()

为了查看sql语句方便我们加入调试，在settings.py文件中配置

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'handlers': {
        'console':{
            'level':'DEBUG',
            'class':'logging.StreamHandler',
        },
    },
    'loggers': {
        'django.db.backends': {
            'handlers': ['console'],
            'propagate': True,
            'level':'DEBUG',
        },
    }
}

查询数据

# INNER JOIN
>>> from myproject.myapp.models import User,Article
>>> list = Article.objects.filter(user_id = 2).values('user__first_name', 'user__last_name', 'title', 'user_id', 'add_date').order_by('add_date')
>>> print(list)
(0.004) SELECT "myapp_user"."first_name", "myapp_user"."last_name", "myapp_article"."title", "myapp_article"."user_id", "myapp_article"."add_date" FROM "myapp_article" INNER JOIN "myapp_user" ON ("myapp_article"."user_id" = "myapp_user"."id") WHERE "myapp_article"."user_id" = 2 ORDER BY "myapp_article"."add_date" ASC LIMIT 21; args=(2,)
<QuerySet [{'user__first_name': '小', 'user__last_name': '华', 'title': '小华写了第一篇文章', 'user_id': 2, 'add_date': datetime.date(2020, 12, 9)}, {'user__first_name': '小', 'user__last_name': '华', 'title': '小华写了第二篇文章', 'user_id': 2, 'add_date': datetime.date(2020, 12, 9)}]>
  
# LEFT JOIN
>>> list1 = User.objects.filter(id=2).values('first_name', 'last_name', 'article__title', 'article__add_date').order_by('article__add_date')
>>> print(list1)
(0.002) SELECT "myapp_user"."first_name", "myapp_user"."last_name", "myapp_article"."title", "myapp_article"."add_date" FROM "myapp_user" LEFT OUTER JOIN "myapp_article" ON ("myapp_user"."id" = "myapp_article"."user_id") WHERE "myapp_user"."id" = 2 ORDER BY "myapp_article"."add_date" ASC LIMIT 21; args=(2,)
<QuerySet [{'first_name': '小', 'last_name': '华', 'article__title': '小华写了第一篇文章', 'article__add_date': datetime.date(2020, 12, 9)}, {'first_name': '小', 'last_name': '华', 'article__title': '小华写了第二篇文章', 'article__add_date': datetime.date(2020, 12, 9)}]>

修改数据

>>> user = User.objects.get(id = 1)
(0.000) SELECT "myapp_user"."id", "myapp_user"."first_name", "myapp_user"."last_name" FROM "myapp_user" WHERE "myapp_user"."id" = 1 LIMIT 21; args=(1,)
>>> user.last_name = "荣"
>>> user.save()
(0.009) UPDATE "myapp_user" SET "first_name" = '小', "last_name" = '荣' WHERE "myapp_user"."id" = 1; args=('小', '荣', 1)

删除数据

>>> del_user = User.objects.filter(last_name='荣')
>>> del_user.delete()
(0.000) SELECT "myapp_user"."id", "myapp_user"."first_name", "myapp_user"."last_name" FROM "myapp_user" WHERE "myapp_user"."last_name" = '荣'; args=('荣',)
(0.000) BEGIN; args=None
(0.003) DELETE FROM "myapp_article" WHERE "myapp_article"."user_id" IN (1); args=(1,)
(0.000) DELETE FROM "myapp_user" WHERE "myapp_user"."id" IN (1); args=(1,)
(2, {'myapp.Article': 1, 'myapp.User': 1})

Django干货知识分享，ORM模型（二）