记录Django开发心得
概念层面
概括
Django是属于MVC的Web框架。
Model：负责与数据库打交道
View：负责获取或者增强从Models得到的数据
Controller：这是Django本身
Project与App的区别
Project:提供各种配置文件 App:功能的结合，包括Model和view，需要在根目录下添加”__init__.py”，使得Python可以识别
ManyToMany与ForeignKey的区别
ForeignKey例子：
员工打卡上班的记录——员工可有多次打卡记录，但是一次刷卡记录只能有单一员工属性（一对多）
ManyToMany例子:
一篇文章可以有多个标签，而一个标签对应的文章也可以是多篇的（多对多）
ManyToMany还有一种特殊的结构，非常类似Twitter的Follow。
假设 A Follow了 B，但是B并没有Follow A，他们之间的Follow是不对等的，要实现这种关系，要在Meta里面设置symetric=False
SexyCode
这是我理解后觉得“性感到死”的一些代码：
lambda x, y: x+y
Lambda其实和JS中的匿名函数有这异曲同工的作用，嫌起名麻烦，就丢进去，Lambda默认返回里面的值，所以不需要return
map(lambda x: x+1, [1,2,3]) #得到[2,3,4]
也就是每个都执行一次前面的函数
reduce(lambda x, y: x+y, [1,2,3]) #得到6
也就是每个都和之前的元素执行一次操作
[i for i in xrange(0,100) if i%2==0]
得到100以下所有偶数。学术上叫“列表推导”，但在现实案例中是遍历的好工具。
Q(**{key:value})
我在培训的时候，学到的是Q、F这两个Django函数是不接受字符串的，即 Q("abc=1") 是不能接受的。但是这段代码性感之处就是彻底摆脱了这条束缚（其实就是重写了keyword对），可以随意构造你喜欢的查询段，这在构造搜索功能时十分有用。比如：
q_dict = reduce(lambda x,y: x&y, [ Q(**{"%s__slug_name" % taxonomy:request.GET.get(taxonomy)}
) for taxonomy in request.GET.keys() if taxonomy in SEARCHABLE_LIST ])
@property
这个@符号的用法叫“修饰器”，个人感觉这是python比其他语言优美的地方，如何构造修饰器的话，还是看文档的好。这里只是说在class中使用 @property 的话，这个函数就自动地变成class的属性了，这和js的set、get很像
super超类的使用，super一出，继承的子class一概不执行自身的函数，而是执行super指定的函数
annotate和aggregate。这两个家伙在构造新的query_set时非常有用。比如要统计出一台电脑的总价时，在ComputerManager里面使用
def get_query_set(self):
query_set = super(ComputerManager, self).get_query_set()
query_set = query_set.annotate(price=Sum('devices__price'))
这样，每台电脑就有了总价格。这在构造商品集的时候很方便，但是admin.py的编写就略显罗嗦了。
Error集
取出数据时：XXManager object is not iterable
这是因为Django不会在执行代码过程中得出SQL语句并查询（所以想获得Sql语句也是不可能的）。所以需要使用.get(),.all(),.filter来获得真正的数据实体
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