#关系对象#
from django.db import models
class Blog(models.Model):
name = models.CharField(max_length=100)
tagline = models.TextField()
def __str__(self):
return self.name
class Author(models.Model):
name = models.CharField(max_length=50)
email = models.EmailField()
def __str__(self):
return self.name
class Entry(models.Model):
blog = models.ForeignKey(Blog)
headline = models.CharField(max_length=255)
body_text = models.TextField()
pub_date = models.DateTimeField()
authors = models.ManyToManyField(Author)
def __str__(self):
return self.headline
例如，b是Blog的对象， b.entry_set就能够得到Entry的对象，就能够操做
1 Entry.objects.filter(blog__name__exact='Beatles Blog')，查找blog的对象的数据
2 Blog.objects.filter(entry__headline__contains='Lennon')， 反过来也能够
3 select_related(),表示能够把第一次查找的数据加入到缓存，第二次查找就到缓存里面查找
e = Entry.objects.select_related().get(id=2)
print e.blog
print e.blog
4. XXX_set 至关于得到XXX表的对象(必须得有一个类的实例，若是用Blog.entry_set, 发生错误)
b = Blog.objects.get(id=1)
b.entry_set.all() # Returns all Entry objects related to Blog.
b.entry_set is a Manager that returns QuerySets.
b.entry_set.filter(headline__contains='Lennon')
b.entry_set.count()
5. related_name 参数
能够重载”XXX_set”名字.举例,若是把”Entry”模型修改成”blog =ForeignKey(Blog, related_name=’entries’)”
6. get_FOO_display()
GENDER_CHOICES = (
('M', 'Male'),
('F', 'Female'),
)
class Person(models.Model):
name = models.CharField(max_length=20)
gender = models.CharField(max_length=1, choices=GENDER_CHOICES)
p = Person(name='John', gender='M')
p.save()
p.gender
‘M’
p.get_gender_display()
'Male'
7. get_object_or_404()
# Get the Entry with a primary key of 3
e = get_object_or_404(Entry, pk=3)
# Get the author of blog instance e with a name of 'Fred'
a = get_object_or_404(e.authors, name='Fred')
# Use a custom manager 'recent_entries' in the search for an
# entry with a primary key of 3
e = get_object_or_404(Entry.recent_entries, pk=3)
8. get_list_or_404()
get_list_or_404 行为与 get_object_or_404() 相同，可是它用 filter() 取代了 get() 。若是列表为空，它将引起 Http404