Django基础之ORM操作

##################################################################
# PUBLIC METHODS THAT ALTER ATTRIBUTES AND RETURN A NEW QUERYSET #
##################################################################

def all(self)
	# 获取所有的数据对象

def filter(self, *args, **kwargs)
	# 条件查询
	# 条件可以是：参数，字典，Q

def exclude(self, *args, **kwargs)
	# 条件查询
	# 条件可以是：参数，字典，Q

def select_related(self, *fields)
	 性能相关：表之间进行join连表操作，一次性获取关联的数据。
	 model.tb.objects.all().select_related()
	 model.tb.objects.all().select_related('外键字段')
	 model.tb.objects.all().select_related('外键字段__外键字段')

def prefetch_related(self, *lookups)
	性能相关：多表连表操作时速度会慢，使用其执行多次SQL查询在Python代码中实现连表操作。
			# 获取所有用户表
			# 获取用户类型表where id in (用户表中的查到的所有用户ID)
			models.UserInfo.objects.prefetch_related('外键字段')



			from django.db.models import Count, Case, When, IntegerField
			Article.objects.annotate(
				numviews=Count(Case(
					When(readership__what_time__lt=treshold, then=1),
					output_field=CharField(),
				))
			)

			students = Student.objects.all().annotate(num_excused_absences=models.Sum(
				models.Case(
					models.When(absence__type='Excused', then=1),
				default=0,
				output_field=models.IntegerField()
			)))

def annotate(self, *args, **kwargs)
	# 用于实现聚合group by查询

	from django.db.models import Count, Avg, Max, Min, Sum

	v = models.UserInfo.objects.values('u_id').annotate(uid=Count('u_id'))
	# SELECT u_id, COUNT(ui) AS `uid` FROM UserInfo GROUP BY u_id

	v = models.UserInfo.objects.values('u_id').annotate(uid=Count('u_id')).filter(uid__gt=1)
	# SELECT u_id, COUNT(ui_id) AS `uid` FROM UserInfo GROUP BY u_id having count(u_id) > 1

	v = models.UserInfo.objects.values('u_id').annotate(uid=Count('u_id',distinct=True)).filter(uid__gt=1)
	# SELECT u_id, COUNT( DISTINCT ui_id) AS `uid` FROM UserInfo GROUP BY u_id having count(u_id) > 1

def distinct(self, *field_names)
	# 用于distinct去重
	models.UserInfo.objects.values('nid').distinct()
	# select distinct nid from userinfo

	注：只有在PostgreSQL中才能使用distinct进行去重

def order_by(self, *field_names)
	# 用于排序
	models.UserInfo.objects.all().order_by('-id','age')

def extra(self, select=None, where=None, params=None, tables=None, order_by=None, select_params=None)
	# 构造额外的查询条件或者映射，如：子查询
	
	UserInfo.objects.extra(where=['headline ? %s'], params=['Lennon'])
	# select * from userinfo where headline > 'Lennon'
	
	UserInfo.objects.extra(where=["foo='a' OR bar = 'a'", "baz = 'a'"])
	# select * from userinfo where (foo='a' OR bar = 'a') and baz = 'a'
	
	UserInfo.objects.extra(select={'new_id': "select col from sometable where othercol > %s"}, select_params=(1,))
		"""
		select 
			id,
			name,
			(select col from sometable where othercol > 1) as new_id
		"""
	UserInfo.objects.extra(select={'new_id': "select id from tb where id > %s"}, select_params=(1,), order_by=['-nid'])

 def reverse(self):
	# 倒序
	models.UserInfo.objects.all().order_by('-nid').reverse()
	# 注：如果存在order_by，reverse则是倒序，如果多个排序则一一倒序


 def defer(self, *fields):
	models.UserInfo.objects.defer('username','id')
	或
	models.UserInfo.objects.filter(...).defer('username','id')
	#映射中排除某列数据

 def only(self, *fields):
	#仅取某个表中的数据
	 models.UserInfo.objects.only('username','id')
	 或
	 models.UserInfo.objects.filter(...).only('username','id')

 def using(self, alias):
	 指定使用的数据库，参数为别名（setting中的设置）
	 
	 models.UserInfo.objects.filter(id=5).using('db1')


##################################################
# PUBLIC METHODS THAT RETURN A QUERYSET SUBCLASS #
##################################################

def raw(self, raw_query, params=None, translations=None, using=None):
	# 执行原生SQL
	models.UserInfo.objects.raw('select * from userinfo where id > 10 ')

	# 如果SQL是其他表时，必须将名字设置为当前UserInfo对象的主键列名
	models.UserInfo.objects.raw('select id as nid from 其他表')

	# 为原生SQL设置参数
	models.UserInfo.objects.raw('select id as nid from userinfo where nid>%s', params=[12,])

	# 将获取的到列名转换为指定列名
	name_map = {'first': 'first_name', 'last': 'last_name', 'bd': 'birth_date', 'pk': 'id'}
	Person.objects.raw('SELECT * FROM some_other_table', translations=name_map)

	# 指定数据库
	models.UserInfo.objects.raw('select * from userinfo', using="default")

################### 原生SQL ###################
from django.db import connection, connections
cursor = connection.cursor()  # cursor = connections['default'].cursor()
cursor.execute("""SELECT * from auth_user where id = %s""", [1])
row = cursor.fetchone() # fetchall()/fetchmany(..)


def values(self, *fields):
	# 获取每行数据为字典格式

def values_list(self, *fields, **kwargs):
	# 获取每行数据为元祖

def dates(self, field_name, kind, order='ASC'):
	# 根据时间进行某一部分进行去重查找并截取指定内容
	# kind只能是："year"（年）, "month"（年-月）, "day"（年-月-日）
	# order只能是："ASC"  "DESC"
	# 并获取转换后的时间
		- year : 年-01-01
		- month: 年-月-01
		- day  : 年-月-日

	models.DatePlus.objects.dates('ctime','day','DESC')

def datetimes(self, field_name, kind, order='ASC', tzinfo=None):
	# 根据时间进行某一部分进行去重查找并截取指定内容，将时间转换为指定时区时间
	# kind只能是 "year", "month", "day", "hour", "minute", "second"
	# order只能是："ASC"  "DESC"
	# tzinfo时区对象
	models.DDD.objects.datetimes('ctime','hour',tzinfo=pytz.UTC)
	models.DDD.objects.datetimes('ctime','hour',tzinfo=pytz.timezone('Asia/Shanghai'))

	"""
	pip3 install pytz
	import pytz
	pytz.all_timezones
	pytz.timezone(‘Asia/Shanghai’)
	"""

def none(self):
	# 空QuerySet对象


####################################
# METHODS THAT DO DATABASE QUERIES #
####################################

def aggregate(self, *args, **kwargs):
   # 聚合函数，获取字典类型聚合结果
   from django.db.models import Count, Avg, Max, Min, Sum
   result = models.UserInfo.objects.aggregate(k=Count('u_id', distinct=True), n=Count('nid'))
   ===> {'k': 3, 'n': 4}

def count(self):
   # 获取个数

def get(self, *args, **kwargs):
   # 获取单个对象

def create(self, **kwargs):
   # 创建对象

def bulk_create(self, objs, batch_size=None):
	# 批量插入
	# batch_size表示一次插入的个数
	objs = [
		models.DDD(name='r11'),
		models.DDD(name='r22')
	]
	models.DDD.objects.bulk_create(objs, 10)

def get_or_create(self, defaults=None, **kwargs):
	# 如果存在，则获取，否则，创建
	# defaults 指定创建时，其他字段的值
	obj, created = models.UserInfo.objects.get_or_create(username='root1', defaults={'email': '1111111','u_id': 2, 't_id': 2})

def update_or_create(self, defaults=None, **kwargs):
	# 如果存在，则更新，否则，创建
	# defaults 指定创建时或更新时的其他字段
	obj, created = models.UserInfo.objects.update_or_create(username='root1', defaults={'email': '1111111','u_id': 2, 't_id': 1})

def first(self):
   # 获取第一个

def last(self):
   # 获取最后一个

def in_bulk(self, id_list=None):
   # 根据主键ID进行查找
   id_list = [11,21,31]
   models.DDD.objects.in_bulk(id_list)
   
   models.User.objects.filter(id__in=[11,21,31])

def delete(self):
   # 删除

def update(self, **kwargs):
	# 更新

def exists(self):
   # 是否有结果
	pass