Python Django 开发 4 ORM

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：

 from django.db import models

 # Create your models here.
 class Publisher(models.Model):
     name = models.CharField(max_length=30)
     address = models.CharField(max_length=50)
     city = models.CharField(max_length=60)
     state_province = models.CharField(max_length=30)
     county = models.CharField(max_length=50)
     website = models.URLField()

     def __str__(self):
         return self.name

 class AuthorInfo(models.Model):
     gender = models.IntegerField()
     brithday = models.DateField()
     join_time = models.DateTimeField()

     def __str__(self):
         return 'this gender:'+ str(self.gender)

 class Author(models.Model):
     frist_name = models.CharField(max_length=30)
     last_name = models.CharField(max_length=40)
     email = models.EmailField()
     detail = models.OneToOneField(AuthorInfo)

     def __str__(self):
         return u'%s %s' % (self.frist_name,self.last_name)

 class Book(models.Model):
     title = models.CharField(max_length=100)
     authors = models.ManyToManyField(Author)
     publisher = models.ForeignKey(Publisher)
     publication_date=models.DateField()

     def __str__(self):
         return self.title

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

 #python shell 下
 >>>Publisher.objects.create(name='cbs1',address='xxx',city='yyy',state_province='zzz',county='China',website='Http://www.do-iot.net')
 >>>Publisher.objects.create(name='cbs2',address='xxx',city='yyy',state_province='zzz',county='China',website='Http://www.do-iot.net')
 >>>Publisher.objects.create(name='cbs3',address='xxx',city='yyy',state_province='zzz',county='China',website='Http://www.do-iot.net')

 >>>AuthorInfo.objects.create(gender=1,brithday='2012-03-12',join_time='2013-03-04 12:21:32')
 >>>AuthorInfo.objects.create(gender=0,brithday='2012-03-12',join_time='2013-03-04 12:21:32')
 >>>AuthorInfo.objects.create(gender=1,brithday='2012-03-12',join_time='2013-03-04 12:21:32')

 >>>Author.objects.create(frist_name='John',last_name='Leb',email='litdev@outlook.com',detail=AuthorInfo.objects.get(id=1))
 >>>Author.objects.create(frist_name='Susan',last_name='Jeerry',email='litdev@qq.com',detail=AuthorInfo.objects.get(id=2))
 >>>Author.objects.create(frist_name='Jerry',last_name='Brith',email='litdev@outlook.com',detail=AuthorInfo.objects.get(id=3))

 >>>b = Book.objects.create(title='book1',publisher=Publisher.objects.get(id=1),publication_date='2015-06-30')
 >>>b.authors.add(Author.objects.get(id=1))
 >>>b = Book.objects.create(title='book2',publisher=Publisher.objects.get(id=2),publication_date='2015-06-30')
 >>>b.authors.add(Author.objects.get(id=2))
 >>>b = Book.objects.create(title='book2',publisher=Publisher.objects.get(id=3),publication_date='2015-06-30')
 >>>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:

 >>>a = Author.objects.get(id=1)
 >>>d = a.detail
 <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:

 >>>d = AuthorInfo.objects.get(id=1)
 >>>a = d.author
 >>>a
 <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：

 >>>b = Book.objects.get(id=1)
 >>>b.publisher
 <Publisher:cbs1>

反向根据出版社查询所有出版的书:

 >>>p = Publisher.objects.get(id=1)
 >>>b_list = p.book_set.all()
 >>>len(b_list)
 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：

 >>>b = Book.objects.get(id=1)
 >>>b.authors.all()
 [<Author: Jack Jeeb>, <Author: Susan leb>]

反向根据作者查询书籍：

 >>>a = Author.objects.get(id=1)
 >>>a.book_set.all()
 [<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