Python Django 開發 4 ORM

第三篇最後寫了，光知道那些基礎的查詢在項目中是沒有什麼卵用的，重點是實體關係映射(ORM),今天學習了，來記錄一下，關鍵詞:ForeignKey（多對一）、OneToOneField（一對一）、ManyToManyField（多對多）

實體定義：

 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中簡單拖了個模型：

一個出版社對應多本書，Book中經過外鍵ForeignKey來指定，一本書有多個做者，一個做者也會有多本書，因此這裏是多對多關係(ManyToManyField),一個做者Author又會有詳細信息，這裏應該是一對一的關係(OneToOneField)，最下面的表book_authors是Book實體中定義的ManyToManyField字段自動生成的，下面來插入數據

 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))

一對一和一對多添加的方式差很少，多對多的須要先添加除ManyToManyField字段的數據，再在這個實體上添加ManyToManyField關聯的對象,原先我數據都插入好了，這裏寫的都是現場手打的數據，可能會有bug，下面看下查詢的方法

一對一OneToOneField:

經過用戶查詢用戶詳細信息:

1 >>>a = Author.objects.get(id=1)
2 >>>d = a.detail
3 <AuthorInfo:this gender:1>

也能夠反向根據用戶詳細信息查詢用戶基本信息:

1 >>>d = AuthorInfo.objects.get(id=1)
2 >>>a = d.author
3 >>>a
4 <Author:Jack Jeeb>

這裏注意反向查詢要使用表關聯的對象的小寫類名

一對多ForeignKey:

經過書籍信息查詢所屬出版社信息：

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

反向根據出版社查詢全部出版的書:

1 >>>p = Publisher.objects.get(id=1)
2 >>>b_list = p.book_set.all()
3 >>>len(b_list)
4 2

注意這裏查詢使用小寫關聯的類名+"_set"來查詢，後面的all()就跟普通的查詢同樣了，where、order_by等等

多對多ManyToManyField：

根據書籍查詢做者：

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

反向根據做者查詢書籍：

1 >>>a = Author.objects.get(id=1)
2 >>>a.book_set.all()
3 [<Book:book1>]

跟一對多反向查詢差很少

理解這些一通常項目數據層都沒有問題了(經驗、畢竟是作了兩三年的asp.net開發的大水B)

 

PS參考資料：

http://logic0.blog.163.com/blog/static/18892814620137343447299/

http://blog.csdn.net/fengyu09/article/details/17434795