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先看一下数据库模型之间的对应关系:
Author n:n Book n:1 Publisher
然后看看在python项目中的models.py中如何表示:
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)
country = models.CharField(max_length=50)
website = models.URLField()
class Author(models.Model):
first_name = models.CharField(max_length=30)
last_name = models.CharField(max_length=40)
email = models.EmailField(blank=True,verbose_name='e-mail')
class Book(models.Model):
title = models.CharField(max_length=100)
authors = models.ManyToManyField(Author)
publisher = models.ForeignKey(Publisher)
publication_date = models.DateField(blank=True, null=True)
下面看看如何插入数据:
方法一:
p1 = Publisher(name='Addison-Wesley', address='75 Arlington Street',city='Boston', state_province='MA', country='U.S.A.',website='http://www.apress.com/')
p1.save()
方法二:
p1 = Publisher.objects.create(name='Apress',address='2855 Telegraph Avenue',city='Berkeley', state_province='CA', country='U.S.A.',website='http://www.apress.com/')
更新数据:
方法一:
p1.name = 'Apress Publishing'
p1.save()
方法二:
Publisher.objects.filter(id=1).update(name='Apress Publishing')
注意:
第一种方法更新数据库中所有的字段,
生成数据库语句是:
UPDATE book_publisher SET
name = 'Apress Publishing',
address = '2855 Telegraph Ave.',
city = 'Berkeley',
state_province = 'CA',
country = 'U.S.A.',
website = 'http://www.apress.com'
WHERE id = 52;
第二种数据库语句是:
UPDATE books_publisher
SET name = 'Apress Publishing'
WHERE id = 52;
更新所有记录
Publisher.objects.all().update(country='USA')
下面是选择对象:
Publisher.objects.all() 选择所有
Publisher.objects.filter(name= ‘ Apress ’ ) 数据过滤
Publisher.objects.filter(name__contains="press")
Publisher.objects.get(name= “ Apress ” ) 获取单个对象
注意: filter()`` 函数返回一个记录集,这个记录集是一个列表 QuerySet 。相对列表来说,有些时候我们更需要获取单个的对 象, 用 `` get()`` 方法。
Get ()方法:
如果结果是多个对象,会导致抛出异常;
如果查询没有返回结果也会抛出异常。
contains转换成数据库语句是like
下面是删除对象:
p = Publisher.objects.get(name="dddddddddddd")
p.delete()
或者
Publisher.objects.filter(country='USA').delete()
Publisher.objects.all().delete()
下面是访问外键---一对多访问:
b = Book.objects.get(id= 1 )
b.publisher
b.publisher.website
访问外键---多对一访问:
p = Publisher.objects.get(name='Apress Publishing')
p.book_set.all()
p.book_set.filter(name__icontains='django')
访问外键---多对多访问:
b = Book.objects.get(id= 2 )
b.authors.all()
b.authors.filter(first_name='Adrian')
b.authors.filter(first_name='Adam')
访问外键---多对多访问(反向):
a = Author.objects.get(first_name='Adrian', last_name='Holovaty')
a.book_set.all()
大家可能纳闷什么时候用xxx_set来得到想要的对象呢?
其实可以回去看看models.py,其中book中有这两句:
authors = models.ManyToManyField(Author)
publisher = models.ForeignKey(Publisher)
所以当模型中有约束则用b.publisher和b.authors.all(),相反模型中没有约束就用a.book_set.all()等。 |
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