• 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
    

      

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  • 原文地址:https://www.cnblogs.com/yang-wei/p/10009114.html
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