django 多表操作

三种关系一对一，一对多，多对多

创建表

 1 一对一
 2     xx = models.OneToOneField(to='表名',to_field='字段名',on_delete=models.CASCADE)  #删除时的一些级联效果,to_field可以不写,默认是关联到另一张表的主键,on_delete在1.x版本的django中不用写,默认是级联删除的,2.x版本的django要写.
 3     
 4 一对多
 5     xx = models.ForeignKey(to='表名',to_field='字段名',on_delete=models.CASCADE)
 6 多对多
 7     xx = models.ManyToManyField(to='另外一个表名') #这是自动创建第三表
 8     
 9 示例
10     from django.db import models
11 
12 # Create your models here.
13 
14 from django.db import models
15 
16 # Create your models here.
17 #作者表
18 class Author(models.Model): #比较常用的信息放到这个表里面
19     name=models.CharField( max_length=32)
20     age=models.IntegerField()
21     # authorDetail=models.OneToOneField(to="AuthorDetail",to_field="nid",on_delete=models.CASCADE)
22     authorDetail=models.OneToOneField(to='AuthorDetail')  #一对一到AuthorDetail表  生成为表字段之后,会自动变为authorDetail_id这样有一个名称
23 
24     # 外键字段 -- 外键字段名_id
25 
26     # foreign+unique
27 
28     def __str__(self):
29         return self.name
30 
31 #作者详细信息表
32 class AuthorDetail(models.Model):
33     birthday=models.DateField()
34     # telephone=models.BigIntegerField()
35     telephone=models.CharField(max_length=32)
36     addr=models.CharField( max_length=64)
37     def __str__(self):
38         return self.addr
39 
40 
41 #出版社表   和 书籍表 是 一对多的关系
42 class Publish(models.Model):
43     name=models.CharField( max_length=32)
44     city=models.CharField( max_length=32)
45     email=models.EmailField()  #charfield -- asdfasdf
46     def __str__(self):
47         return self.name
48 
49 #书籍表
50 class Book(models.Model):
51     nid = models.AutoField(primary_key=True)
52     title = models.CharField( max_length=32)
53     publishDate=models.DateField()
54     price=models.DecimalField(max_digits=5,decimal_places=2)  #decimal(16,2)
55     publishs=models.ForeignKey(to="Publish")
56     authors=models.ManyToManyField(to='Author',)
57 
58     def __str__(self):
59         return self.title
60 
61 #手动创建第三张表,暂时忽略
62 # class BookToAuthor(models.Model):
63 #     book_id = models.ForeignKey(to='Book')
64 #     author_id = models.ForeignKey(to='Author')
65 #     # xx = models.CharField(max_length=12)

增删改查

增

 1 #1 增
 2     #1.1 一对一增加
 3     # new_author_detail = models.AuthorDetail.objects.create(
 4     #     birthday='1979-08-08',
 5     #     telephone='138383838',
 6     #     addr='黑龙江哈尔滨'
 7     # )
 8     # obj = models.AuthorDetail.objects.filter(addr='山西临汾').first()
 9 
10     #方式1
11     # models.Author.objects.create(
12     #     name='王涛',
13     #     age='40',
14     #     authorDetail=new_author_detail,
15     # )
16     # 方式2  常用
17     # models.Author.objects.create(
18     #     name='王涛',
19     #     age='40',
20     #     authorDetail_id=obj.id,
21     # )
22 
23     # 一对多
24     #方式1
25     # obj = models.Publish.objects.get(id=2)
26     # models.Book.objects.create(
27     #     title = '李帅的床头故事',
28     #     publishDate='2019-07-22',
29     #     price=3,
30     #     # publishs=models.Publish.objects.get(id=1),
31     #     publishs=obj,
32     #
33     # )
34     # 方式2 常用
35     # models.Book.objects.create(
36     #     title='李帅的床头故事2',
37     #     publishDate='2019-07-21',
38     #     price=3.5,
39     #     # publishs=models.Publish.objects.get(id=1),
40     #     publishs_id=obj.id
41     #
42     # )
43 
44     # 多对多
45     # 方式1   常用
46     # book_obj = models.Book.objects.get(nid=1)
47     # book_obj.authors.add(*[1,2])
48     # 方式2
49     # author1 = models.Author.objects.get(id=1)
50     # author2 = models.Author.objects.get(id=3)
51     # book_obj = models.Book.objects.get(nid=5)
52     # book_obj.authors.add(*[author1,author2])

删

 1 一对一和一对多的删除和单表删除是一样的
 2 # 一对一  表一外键关联到表二,表一删除,不影响表2,表2删除会影响表1
 3     # models.AuthorDetail.objects.get(id=2).delete()
 4     # models.Author.objects.get(id=3).delete()
 5 
 6     # 一对多
 7     # models.Publish.objects.get(id=1).delete()
 8     # models.Book.objects.get(nid=1).delete()
 9 
10     # 多对多关系删除
11     # book_obj = models.Book.objects.get(nid=6)
12     # book_obj.authors.remove(6)
13     # book_obj.authors.remove(*[5,6])
14     # book_obj.authors.clear()
15     # book_obj.authors.add(*[1,])
16     # book_obj.authors.set('1')
17     # book_obj.authors.set(['5','6']) #删除然后更新

更新

 1  # 更新
 2     # 一对一
 3     # models.Author.objects.filter(id=5).update(
 4     #     name='崔老师',
 5     #     age=16,
 6     #     # authorDetail=models.AuthorDetail.objects.get(id=5),
 7     #     authorDetail_id=4,
 8     # )
 9     #一对多
10     # models.Book.objects.filter(pk=4).update(
11     #     title='B哥的往事2',
12     #     # publishs=models.Publish.objects.get(id=3),
13     #     publishs_id=3,
14     # )
15     
16     #一对多
17     models.Publish.objects.filter(pk=2).update(
18         id=4, # 没有级联更新,报错!!
19     )