class User(models.Model):
    username = models.CharField(max_length=20, default='')
    password = models.CharField(max_length=200, default='')

    def __str__(self):
        return " User: {}".format(self.username)

class UserExtension(models.Model):
    nickname = models.CharField(max_length=50)
    sex = models.CharField(max_length=50)
    age = models.IntegerField()

    user = models.OneToOneField("User", on_delete=models.CASCADE)

# 查看扩展表中的对应用户信息
ex = UserExtension.objects.first()
print(ex.user)

# 通过用户获取扩展表信息
user = User.objects.first() # 获取一个用户
print(user) 

res = user.userextension 
print(res)

user = User.objects.first() # 获取一个用户
print(user)

res = user.gugu
print(res)

category =     Category.objects.all()
category.article_set.all() # 字段_set

mysql> show engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                        | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| InnoDB             | YES     | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                          | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables      | NO           | NO   | NO         |
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) | NO           | NO   | NO         |
| MyISAM             | DEFAULT | MyISAM storage engine                                          | NO           | NO   | NO         |
| CSV                | YES     | CSV storage engine                                             | NO           | NO   | NO         |
| ARCHIVE            | YES     | Archive storage engine                                         | NO           | NO   | NO         |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                             | NO           | NO   | NO         |
| FEDERATED          | NO      | Federated MySQL storage engine                                 | NULL         | NULL | NULL       |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
9 rows in set (0.00 sec)

from django.db import models

# Create your models here.
class User(models.Model):
    username = models.CharField(max_length=20, default='')
    password = models.CharField(max_length=200, default='')

class Article(models.Model):
    title = models.CharField(max_length=100)
    content = models.TextField()

    user = models.ForeignKey("User", on_delete=models.CASCADE)

from django.http import HttpResponse
from .models import  User, Article

# 添加操作
def add(request):
    user = User(username="张三", password="123456")
    user.save() # 保存
    article = Article(title='文章标题1', content='文章噢！')
    article.user = user
    article.save()

    return HttpResponse("Add Ok!")

# 删除操作
def delete(request):
    user = User(pk=1)
    user.delete()
    return HttpResponse("Delete")

class User(models.Model):
    username = models.CharField(max_length=20, default='')
    password = models.CharField(max_length=200, default='')

class Article(models.Model):
    title = models.CharField(max_length=100)
    content = models.TextField()

    user = models.ForeignKey("User", on_delete=models.CASCADE)

user = User(username="张三", password="123456")
user.save()

article = Article(title='文章标题1', content='文章噢！')

article.user = user # 指定文章的作者是上面保存的User
article.save()

def search(request):
    # 获取某个用户下所有文章
    user = User.objects.first() # 获取一个用户
    print(user)

    artlist = user.article_set.all() # 获取用户的文章
    print(artlist)


    return HttpResponse("Search")

>>> 
 User: 李四
<QuerySet [<Article: Article: 文章标题1>, <Article: Article: 文章标题3>]>

def add(request):
    user = User.objects.first() # 获取一个用户
    print(user)
  
    article = Article(title="bbb", content="asdasd5")

    user.article_set.add(article, bulk=False) # 用户添加一个文章
    
    # bulk = False 表示上面的article可以不用保存就可以存储。Django已经为我们做了操作

    return HttpResponse("Add Success")

class Article(models.Model):
    title = models.CharField(max_length=100)
    content = models.TextField()

    tags = models.ManyToManyField("Tag", related_name="tags")

    def __str__(self):
        return "Article: {}".format(self.title)

class Tag(models.Model):
    name = models.CharField(max_length=50)

# 获取某个文章下的所有标签
article = Article.objects.first()

taglist = article.tags.all()
print(taglist)

article = Article.objects.first()
tag = Tag('热门文章')
tag.save()

article.tag_set.add(tag) 

class Person(models.Model):
    age = models.IntegerField()
    name = models.CharField(max_length=100)

    @property
    def all_cars(self):
        return self.cars.all()

    @property
    def message(self):
        return '{}-{}'.format(self.name, self.age)

    class Meta:
        db_table = 'person'

    def __str__(self):
        return "<Person: {}>".format(self.name)


class Car(models.Model):
    owner = models.ForeignKey(Person, on_delete=models.CASCADE, related_name='cars')
    name = models.CharField(max_length=64)
    price = models.FloatField()

    class Meta:
        db_table = 'car'

# 子表查询主表
In [3]: car = Car.objects.get(id=1)
    
In [4]: car
Out[4]: <Car: Car object (1)>
        
In [6]: print(car.owner.name)
Luck

# 主表查子表
    # 方式一
    # Django默认每个主表对象都有一个外键的属性
    # 可以通过它来查询所有属于主表的子表信息
    # 查询方式：主表.子表_set()
    # 返回值为一个queryset对象
luck.car_set().all()
    
    # 方式二：
    # 通过在外键中设置related_name属性值既可
luck.cars.all()

    # 方式三：
    # 通过@property装饰器在model中预定义方法实现
luck = Person.objects.filter(id=1).first()
print(luck.all_cars)

app.模型的名字