from django.db import models

class Blog(models.Model):
    name = models.CharField(max_length=100)
    tagline = models.TextField()

    def __str__(self):              # __unicode__ on Python 2
        return self.name

class Author(models.Model):
    name = models.CharField(max_length=50)
    email = models.EmailField()

    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()

    def __str__(self):              # __unicode__ on Python 2
        return self.headline

>>> from blog.models import Blog
>>> b = Blog(name=‘Beatles Blog‘, tagline=‘All the latest Beatles news.‘)
>>> b.save()

>>> b5 = Blog.objects.get(pk=1)
>>> b5.name = ‘New name‘
>>> b5.save()

>>> from blog.models import Entry
>>> entry = Entry.objects.get(pk=1)
>>> cheese_blog = Blog.objects.get(name="Cheddar Talk")
>>> entry.blog = cheese_blog
>>> entry.save()

>>> from blog.models import Author
>>> joe = Author.objects.create(name="Joe")
>>> entry.authors.add(joe)

>>> john = Author.objects.create(name="John")
>>> paul = Author.objects.create(name="Paul")
>>> george = Author.objects.create(name="George")
>>> ringo = Author.objects.create(name="Ringo")
>>> entry.authors.add(john, paul, george, ringo)

>>> all_entries = Entry.objects.all()     # all() 一个结果集（列表）包含所有数据库表的记录

 1 Entry.objects.filter(pub_date__year=2006)       查询所有发布日期是2006的entry
 2 Entry.objects.all().filter(pub_date__year=2006)   # 等同上面语句
 3 
 4 支持链式查询
 5 
 6 >>> Entry.objects.filter(
 7 ...     headline__startswith=‘What‘
 8 ... ).exclude(
 9 ...     pub_date__gte=datetime.date.today()
10 ... ).filter(
11 ...     pub_date__gte=datetime(2005, 1, 30)
12 ... )
13 
14 
15 filter 查询是独立的，q2,q3,不影响q1的结果
16 
17 >>> q1 = Entry.objects.filter(headline__startswith="What")
18 >>> q2 = q1.exclude(pub_date__gte=datetime.date.today())
19 >>> q3 = q1.filter(pub_date__gte=datetime.date.today())

>>> q = Entry.objects.filter(headline__startswith="What")
>>> q = q.filter(pub_date__lte=datetime.date.today())
>>> q = q.exclude(body_text__icontains="food")
>>> print(q)

前面三条语句并没有真正从数据库获取数据，直到第四条语句，我们去打印起结果时，才真正从数据库获取数据

当我们明确知道只有一条记录满足我们的查询时，我们可以使用get(),
>>> one_entry = Entry.objects.get(pk=1)

注意：在使用get时，如果只有有多条记录满足，django 将抛出MultipleObjectsReturned异常,而使用filter方法时,则返回多个记录的列表;而没有记录满足时，get()将抛出DoesNotExist;filter没有异常抛出，只返回空列表

Entry.objects.all()[:5]     # 返回entry的前5条记录，相当于select * from entry limit 5；

Entry.objects.all()[5:10]    # 返回第六到第十条记录，相当于 select * from entry limit 5 offset 5;

Entry.objects.all()[-1]    # 不支持负索引

Entry.objects.all()[:10:2]     #指定切片的步长

Entry.objects.order_by(‘headline‘)[0]   #entry 按headline 字段排序后，取第一条记录。相当于 select * from entry  order by limit 1；

语法格式： field__lookuptype=value   (双下划线)

>>> Entry.objects.filter(pub_date__lte=‘2006-01-01‘)

相当于：
SELECT * FROM blog_entry WHERE pub_date <= ‘2006-01-01‘;


field 必须是models class  的 field的名称

除了双下划线这种格式，还有一种形式，外键字段名称接_id,

Entry.objects.filter(blog_id=4)     #查询所有属于 id = 4 的 blog 的entry对象


exact：

Entry.objects.get(headline__exact="Cat bites dog")    #精确匹配查询；相当于：SELECT ... WHERE headline = ‘Cat bites dog‘;

Blog.objects.get(id=14) 相当于 Blog.objects.get(id__excat=14)


iexact:

大小写不敏感的字符匹配

>>> Blog.objects.get(name__iexact="beatles blog")

  Would match a Blog titled "Beatles Blog", "beatles blog", or even "BeAtlES blOG".

contains 与同样有icontains:

模糊匹配

Entry.objects.get(headline__contains=‘Lennon‘) 相当于sql： SELECT ... WHERE headline LIKE ‘%Lennon%‘;

startswith, endswith，istartswith, iendswith


Entry.objects.filter(blog__name=‘Beatles Blog‘)  #This example retrieves all Entry objects with a Blog whose name is ‘Beatles Blog‘:

相当于sql：




也支持反向操作：

Blog.objects.filter(entry__headline__contains=‘Lennon‘) #This example retrieves all Blog objects which have at least one Entry whose headline contains ‘Lennon‘:

相当于sql：