写的很乱，写的时候思路不够清晰
django中模型多对多关系
# 模型类代码
class Blog(models.Model):
name = models.CharField(max_length=100)
tagline = models.TextField()
class Meta:
managed = True
db_table = 'Blog'
def __str__(self): # __unicode__ on Python 2
return self.name
class Author(models.Model):
name = models.CharField(max_length=50)
email = models.EmailField()
class Meta:
managed = True
db_table = 'Author'
def __str__(self): # __unicode__ on Python 2
return self.name
class Entry(models.Model):
blog = models.ForeignKey(Blog)
headline = models.CharField(max_length=255)
body_text = models.TextField()
pub_date = models.DateField()
mod_date = models.DateField()
authors = models.ManyToManyField(Author)
n_comments = models.IntegerField()
n_pingbacks = models.IntegerField()
rating = models.IntegerField()
class Meta:
managed = True
db_table = 'Entry'
def __str__(self): # __unicode__ on Python 2
return self.headline
ForeignKey外键约束，在django中是表示一对多的关系。
ManyToManyField 两张表建立多对多关系，本质是建立中间表关联
数据库表展示
# 形成了一张中间表Entry_authors
MariaDB [celvin]> desc Blog;
+---------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(100) | NO | | NULL | |
| tagline | longtext | NO | | NULL | |
+---------+--------------+------+-----+---------+----------------+
3 rows in set (0.02 sec)
MariaDB [celvin]> desc Author;
+-------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(50) | NO | | NULL | |
| email | varchar(254) | NO | | NULL | |
+-------+--------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
MariaDB [celvin]> desc Entry;
+-------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| headline | varchar(255) | NO | | NULL | |
| body_text | longtext | NO | | NULL | |
| pub_date | date | NO | | NULL | |
| mod_date | date | NO | | NULL | |
| n_comments | int(11) | NO | | NULL | |
| n_pingbacks | int(11) | NO | | NULL | |
| rating | int(11) | NO | | NULL | |
| blog_id | int(11) | NO | MUL | NULL | |
+-------------+--------------+------+-----+---------+----------------+
9 rows in set (0.00 sec)
MariaDB [celvin]> desc Entry_authors;
+-----------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+---------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| entry_id | int(11) | NO | MUL | NULL | |
| author_id | int(11) | NO | MUL | NULL | |
+-----------+---------+------+-----+---------+----------------+
3 rows in set (0.00 sec)
插入测试数据：
Blog:
insert into Blog values(1,"天龙八部","虚构");
insert into Blog values(2,"武林外传","虚构");
insert into Blog values(3,"神雕侠侣","虚构");
insert into Blog values(4,"笑傲江湖","虚构");
insert into Blog values(5,"未知世界","虚构");
Author:
insert into Author values(1,"金庸","111111111@qq.com");
insert into Author values(2,"古龙","222222222@qq.com");
insert into Author values(3,"韩寒","333333333@qq.com");
Entry:
insert into Entry values (1,"虚构","1111111111",now(),now(),1,1,1,1);
insert into Entry values (2,"虚构","2222222222",now(),now(),1,1,1,2);
insert into Entry values (3,"虚构","3333333333",now(),now(),1,1,1,3);
insert into Entry values (4,"虚构","4444444444",now(),now(),1,1,1,4);
insert into Entry values (5,"虚构","5555555555",now(),now(),1,1,1,5);
测试保存外键字段：
>>> from blog.models import Entry
>>> entry = Entry.objects.get(pk=1)
>>> cheese_blog = Blog.objects.get(name="未知世界")
>>> entry.blog = cheese_blog
>>> entry.save()
# 结果，entry中的blog外键修改，数据源自blog表中的主键，将外键字段与对象对应起来，save即可
MariaDB [celvin]> select * from Entry where id=1;
+----+----------+------------+------------+------------+------------+-------------+--------+---------+
| id | headline | body_text | pub_date | mod_date | n_comments | n_pingbacks | rating | blog_id |
+----+----------+------------+------------+------------+------------+-------------+--------+---------+
| 1 | 虚构 | 1111111111 | 2017-08-17 | 2017-08-17 | 1 | 1 | 1 | 5 |
+----+----------+------------+------------+------------+------------+-------------+--------+---------+
测试保存ManyToManyField字段：
>>> entry = Entry.objects.get(pk=1)
>>> joe = Author.objects.create(name="Joe")
>>> entry.authors.add(joe)
# 结果，多对多关系中间表数据
MariaDB [celvin]> select * from Entry_authors;
+----+----------+-----------+
| id | entry_id | author_id |
+----+----------+-----------+
| 1 | 1 | 4 |
+----+----------+-----------+
# 将pk=1的entry对象关联author对象，插入到中间表中
跨关联关系的查询
# 查找entry里中blog，是未知世界的所有对象，固定写法双下斜杠，__
entrylist = Entry.objects.filter(blog__name='未知世界')
django关联关系：
一对多关联关系，两表之间是ForeignKey关系
多对多关联关系，两表之间是ManyToManyField关系，创建中间的关系表,(数据库一共三张表)
跨关联关系的查询：
# 一对多关系查询：
Entry.objects.filter(blog__name='Beatles Blog')
查询获取entry对象，条件是entry对象的外键字段blog_id与blog类且name字段为Beatles Blog的id相等
# 跨越任意深度??
# 多对多关联关系查询，使用的前提是在建立数据库模型的时候，是采用ManyToManyField的关系
enlist = Entry.objects.filter(authors__name='joe')
