Django 之奇技淫巧 Model

Django Model

1. RuntimeWarning: DateTimeField received a naive datetime

USE_TZ = False

禁用掉时区设置，通通使用系统时间，所以要保证设置了正确的系统时间
TIME_ZONE = 'Asia/Shanghai
如果启用了时区设置，可以设置应用独立的时间

2. 级联删除

wechat_user = models.ForeignKey(Wechat_User,verbose_name=u'微信',blank=True,null=True,on_delete=models.SET_NULL)

CASCADE: 默认级联删除
PROTECT: 通过抛出 django.db.models.ProtectedErrordjango.db.models.ProtectedError 错误来阻止删除关联的对象
SET_NULL: 前置条件需要设定 null=True，设置 ForeignKey 为 Null
SET_DEFAULT: 前置条件需要先设定默认值，设置 ForeignKey 为默认值
SET: 设置为某个方法返回的值
DO_NOTHING: 保留原样，如果再次把外键的对象添加回来，会再次显示。如果数据库设置必须关联则会报 IntegrityError 错。

||13	||哈哈哈哈哈		                ||2016-04-02 23:50:51	||2 || 1||
|| 14	||哈哈哈哈哈哈		         || 2016-04-02 23:56:19	 ||2 ||	1||
||15	||恍恍惚惚恍恍惚惚机会    ||2016-04-03 11:47:21  ||2  ||

上表中 13 14 是设定了 DO_NOTHING；15 是设定了 SET_NULL

3. 关联查询

models.py

class School(models.Model):
    name = models.CharField(max_length=30, verbose_name='school')

class Deparment(models.Model):
	name = models.CharField(max_length=30, verbose_name='department')
	school = models.ForeignKey(School, verbose_name='school')

class StudentClass(models.Model):
	name = models.CharField(max_length=30, verbose_name='class')
	department = models.ForeignKey(Deparment, verbose_name='department')

class StudentYear(models.Model):
	year = models.CharField(max_length=30, verbose_name='year')

class Student(models.Model):
	name = models.CharField(max_length=30, verbose_name='student')
	studentClass = models.ForeignKey(StudentClass, verbose_name='class')
	year = models.ForeignKey(StudentYear, verbose_name='year')

查询的使用用双下划线去关联外键属性，只能过滤 id 的值

>>>school_ids = School.objects.filter(name='EE').values('id')
>>>year_ids = StudentYear.objects.filter(year='2016').values('id')
>>>student = Student.objects.filter(studentClass__department__school_id__in=school_ids, year_id__in=year_ids).first()
		<Student object>

查询是懒惰的，只会在最终序列的时候执行拼接后的语句

utils-89 DEBUG : (0.001) QUERY