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第三篇最后写了，光知道那些基础的查询在项目中是没有什么卵用的，重点是实体关系映射(ORM),今天学习了，来记录一下，关键词:ForeignKey（多对一）、OneToOneField（一对一）、ManyToManyField（多对多）
实体定义：
1 from django.db import models 2 3 # Create your models here. 4 class Publisher(models.Model): 5 name = models.CharField(max_length=30) 6 address = models.CharField(max_length=50) 7 city = models.CharField(max_length=60) 8 state_province = models.CharField(max_length=30) 9 county = models.CharField(max_length=50) 10 website = models.URLField() 11 12 def __str__(self): 13 return self.name 14 15 class AuthorInfo(models.Model): 16 gender = models.IntegerField() 17 brithday = models.DateField() 18 join_time = models.DateTimeField() 19 20 def __str__(self): 21 return ‘this gender:‘+ str(self.gender) 22 23 24 class Author(models.Model): 25 frist_name = models.CharField(max_length=30) 26 last_name = models.CharField(max_length=40) 27 email = models.EmailField() 28 detail = models.OneToOneField(AuthorInfo) 29 30 def __str__(self): 31 return u‘%s %s‘ % (self.frist_name,self.last_name) 32 33 34 35 36 class Book(models.Model): 37 title = models.CharField(max_length=100) 38 authors = models.ManyToManyField(Author) 39 publisher = models.ForeignKey(Publisher) 40 publication_date=models.DateField() 41 42 def __str__(self): 43 return self.title 44 45
在Navicat中简单拖了个模型：
一个出版社对应多本书，Book中通过外键ForeignKey来指定，一本书有多个作者，一个作者也会有多本书，所以这里是多对多关系(ManyToManyField),一个作者Author又会有详细信息，这里应该是一对一的关系(OneToOneField)，最下面的表book_authors是Book实体中定义的ManyToManyField字段自动生成的，下面来插入数据
1 #python shell 下 2 >>>Publisher.objects.create(name=‘cbs1‘,address=‘xxx‘,city=‘yyy‘,state_province=‘zzz‘,county=‘China‘,website=‘Http://www.do-iot.net‘) 3 >>>Publisher.objects.create(name=‘cbs2‘,address=‘xxx‘,city=‘yyy‘,state_province=‘zzz‘,county=‘China‘,website=‘Http://www.do-iot.net‘) 4 >>>Publisher.objects.create(name=‘cbs3‘,address=‘xxx‘,city=‘yyy‘,state_province=‘zzz‘,county=‘China‘,website=‘Http://www.do-iot.net‘) 5 6 >>>AuthorInfo.objects.create(gender=1,brithday=‘2012-03-12‘,join_time=‘2013-03-04 12:21:32‘) 7 >>>AuthorInfo.objects.create(gender=0,brithday=‘2012-03-12‘,join_time=‘2013-03-04 12:21:32‘) 8 >>>AuthorInfo.objects.create(gender=1,brithday=‘2012-03-12‘,join_time=‘2013-03-04 12:21:32‘) 9 10 >>>Author.objects.create(frist_name=‘John‘,last_name=‘Leb‘,email=‘litdev@outlook.com‘,detail=AuthorInfo.objects.get(id=1)) 11 >>>Author.objects.create(frist_name=‘Susan‘,last_name=‘Jeerry‘,email=‘litdev@qq.com‘,detail=AuthorInfo.objects.get(id=2)) 12 >>>Author.objects.create(frist_name=‘Jerry‘,last_name=‘Brith‘,email=‘litdev@outlook.com‘,detail=AuthorInfo.objects.get(id=3)) 13 14 >>>b = Book.objects.create(title=‘book1‘,publisher=Publisher.objects.get(id=1),publication_date=‘2015-06-30‘) 15 >>>b.authors.add(Author.objects.get(id=1)) 16 >>>b = Book.objects.create(title=‘book2‘,publisher=Publisher.objects.get(id=2),publication_date=‘2015-06-30‘) 17 >>>b.authors.add(Author.objects.get(id=2)) 18 >>>b = Book.objects.create(title=‘book2‘,publisher=Publisher.objects.get(id=3),publication_date=‘2015-06-30‘) 19 >>>b.authors.add(Author.objects.get(id=3))
一对一和一对多添加的方式差不多，多对多的需要先添加除ManyToManyField字段的数据，再在这个实体上添加ManyToManyField关联的对象,原先我数据都插入好了，这里写的都是现场手打的数据，可能会有bug，下面看下查询的方法
一对一OneToOneField:
通过用户查询用户详细信息:
1 >>>a = Author.objects.get(id=1) 2 >>>d = a.detail 3 <AuthorInfo:this gender:1>
也可以反向根据用户详细信息查询用户基本信息:
1 >>>d = AuthorInfo.objects.get(id=1) 2 >>>a = d.author 3 >>>a 4 <Author:Jack Jeeb>
这里注意反向查询要使用表关联的对象的小写类名
一对多ForeignKey:
通过书籍信息查询所属出版社信息：
1 >>>b = Book.objects.get(id=1) 2 >>>b.publisher 3 <Publisher:cbs1>
反向根据出版社查询所有出版的书:
1 >>>p = Publisher.objects.get(id=1) 2 >>>b_list = p.book_set.all() 3 >>>len(b_list) 4 2
注意这里查询使用小写关联的类名+"_set"来查询，后面的all()就跟普通的查询一样了，where、order_by等等
多对多ManyToManyField：
根据书籍查询作者：
1 >>>b = Book.objects.get(id=1) 2 >>>b.authors.all() 3 [<Author: Jack Jeeb>, <Author: Susan leb>]
反向根据作者查询书籍：
1 >>>a = Author.objects.get(id=1) 2 >>>a.book_set.all() 3 [<Book:book1>]
跟一对多反向查询差不多
理解这些一一般项目数据层都没有问题了(经验、毕竟是做了两三年的asp.net开发的大水B)
PS参考资料：
http://logic0.blog.163.com/blog/static/18892814620137343447299/
http://blog.csdn.net/fengyu09/article/details/17434795
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原文地址：http://www.cnblogs.com/New-world/p/4611089.html
