这是后面要用到的类
class Blog(models.Model):
name = models.CharField(max_length=100)
tagline = models.TextField() def __unicode__(self):
return self.name class Author(models.Model):
name = models.CharField(max_length=50)
email = models.EmailField() def __unicode__(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()
mod_date = models.DateTimeField()
authors = models.ManyToManyField(Author)
n_comments = models.IntegerField()
n_pingbacks = models.IntegerField()
rating = models.IntegerField() def __unicode__(self):
return self.headline
Creating objects
>>> from blog.models import Blog
>>> b = Blog(name='Beatles Blog', tagline='All the latest Beatles news.')
>>> b.save()
Saving ForeignKey and ManyToManyField fields
>>> 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)
Retrieving objects
>>> Blog.objects
<django.db.models.manager.Manager object at ...>
>>> b = Blog(name='Foo', tagline='Bar')
>>> b.objects
Traceback:
...
AttributeError: "Manager isn't accessible via Blog instances."
Retrieving all objects
>>> all_entries = Entry.objects.all()
filter(**kwargs)
Returns a new QuerySet containing objects that match the given lookup parameters.
exclude(**kwargs)
Returns a new QuerySet containing objects that do not match the given lookup parameters.
Entry.objects.filter(pub_date__year=2006)
Chaining filters
>>> Entry.objects.filter(
... headline__startswith='What'
... ).exclude(
... pub_date__gte=datetime.now()
... ).filter(
... pub_date__gte=datetime(2005, 1, 1)
... )
get,get 方法会返回符合条件的那个元素，当没有符合筛选条件的元素是get方法会抛出一个 DoesNotExist的异常，所以要慎用
>>> one_entry = Entry.objects.get(pk=1)
Field lookups
筛选属性的时候的一些限制条件，基本格式是 field__lookuptype=value，注意是双下划线，下面是lookuptype
exact：Exact match，准确匹配，可以匹配到null（None） iexact： 不区分大小写的准确匹配
contains：包含 icontains：不区分大小写的包含
in：在（一个筛选的列表）里面
gt ：Greater than gte：Greater than or equal to.
lt：Less than. lte：Less than or equal to.
startswith，istartswith，endswith，iendswith
range：pub_date__range=(start_date, end_date))
year，month，day，weekday，
regex:正则表达式匹配，iregex，不区分大小写的
Aggregation functions
聚合函数，针对查询集合的一些操作
Avg：计算平均值，返回值类型float
Count：计算集合的元素个数，返回值类型int
Max，Min，Sum
高级操作
F类：我的理解是返回特定字段的值
例如我想找到所有评论比广播次数多的entry，就可以按照下面这样写
>>> from django.db.models import F
>>> Entry.objects.filter(n_comments__gt=F('n_pingbacks'))
F类返回的是该字段的值，当值是数值的是，可以做算术运算，当时字符串是，可以比较是否相等等运算
pk ：代表primary key
Q类：封装查询已形成更复杂的查询，每个Q查询之间可以用&（and）或者|（or）相连，用逗号相隔表示关系and，Q查询也可以使用~（not）
Poll.objects.get(
Q(question__startswith='Who'),
Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6))
)
#roughly translates into the SQL:
SELECT * from polls WHERE question LIKE 'Who%'
AND (pub_date = '2005-05-02' OR pub_date = '2005-05-06')
注意：Q查询一定要在关键字查询之前，否则查询可能无效
关系查询
1：外键查询，一个类可以通过属性的方法来访问外键的类
>>> e = Entry.objects.get(id=2)
>>> e.blog = some_blog
>>> e.save()
2：一个被外键的类可以通过FOO_set的方法来访问源类，其中Foo是源类
>>> 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()
3：其他的多对一，一对多，一对一的情况可以类比上面这两种情况
如果你不想使用django提供的api接口，那么你可以通过下面两种方式直接运行sql语句
第一种，通过Manager.raw(raw_query, params=None, translations=None)的方法运行sql语句
class Person(models.Model):
first_name = models.CharField(...)
last_name = models.CharField(...)
birth_date = models.DateField(...)
>>> Person.objects.raw('SELECT id, first_name, last_name, birth_date FROM myapp_person')
...
>>> Person.objects.raw('SELECT last_name, birth_date, first_name, id FROM myapp_person')
...
>>> Person.objects.raw('''SELECT first AS first_name,
... last AS last_name,
... bd AS birth_date,
... pk as id,
... FROM some_other_table''')
第二种：完全不用django提供的api，自己建立数据库连接，运行sql查询
def my_custom_sql():
from django.db import connection, transaction
cursor = connection.cursor() # Data modifying operation - commit required
cursor.execute("UPDATE bar SET foo = 1 WHERE baz = %s", [self.baz])
transaction.commit_unless_managed() # Data retrieval operation - no commit required
cursor.execute("SELECT foo FROM bar WHERE baz = %s", [self.baz])
row = cursor.fetchone() return row
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