django中F与Q查询的使用

 from django.db.models import F ret1=models.Product.objects.filter(maichu__gt=F('kucun')) print(ret1)

 models.Product.objects.update(price=F('price')+50)

 from django.db.models.functions import Concat from django.db.models import Value ret3=models.Product.objects.update(name=Concat(F('name'),Value('新款')))

 from django.db.models import Q models.Product.objects.filter(Q(maichu__gt=100)|Q(price__lt=100))

 models.Product.objects.filter(Q(kucun=100)&~Q(maichu=0))

 models.Product.objects.filter(Q(kucun__gt=60), name__contains="新款")

 # 事务 # 买一本 跟老男孩学Linux 书 # 在数据库层面要做的事儿 # 1. 创建一条订单数据 # 2. 去产品表 将卖出数+1， 库存数-1 from django.db.models import F from django.db import transaction # 开启事务处理 try: with transaction.atomic(): # 创建一条订单数据 models.Order.objects.create(num="110110111", product_id=1, count=1) # 能执行成功 models.Product.objects.filter(id=1).update(kucun=F("kucun")-1, maichu=F("maichu")+1) except Exception as e: print(e)

 # extra # 在QuerySet的基础上继续执行子语句 # extra(self, select=None, where=None, params=None, tables=None, order_by=None, select_params=None) # select和select_params是一组，where和params是一组，tables用来设置from哪个表 # Entry.objects.extra(select={'new_id': "select col from sometable where othercol > %s"}, select_params=(1,)) # Entry.objects.extra(where=['headline=%s'], params=['Lennon']) # Entry.objects.extra(where=["foo='a' OR bar = 'a'", "baz = 'a'"]) # Entry.objects.extra(select={'new_id': "select id from tb where id > %s"}, select_params=(1,), order_by=['-nid']) 举个例子： models.UserInfo.objects.extra( select={'newid':'select count(1) from app01_usertype where id>%s'}, select_params=[1,], where = ['age>%s'], params=[18,], order_by=['-age'], tables=['app01_usertype'] ) """ select app01_userinfo.id, (select count(1) from app01_usertype where id>1) as newid from app01_userinfo,app01_usertype where app01_userinfo.age > 18 order by app01_userinfo.age desc """ # 执行原生SQL # 更高灵活度的方式执行原生SQL语句 # 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()

 data = ["".join([str(random.randint(65, 99)) for i in range(4)]) for j in range(100)] obj_list = [models.A(name=i) for i in data] models.A.objects.bulk_create(obj_list) 

 ################################################################## # 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。 总结： 1. select_related主要针一对一和多对一关系进行优化。 2. select_related使用SQL的JOIN语句进行优化，通过减少SQL查询的次数来进行优化、提高性能。 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。 总结： 1. 对于多对多字段（ManyToManyField）和一对多字段，可以使用prefetch_related()来进行优化。 2. prefetch_related()的优化方式是分别查询每个表，然后用Python处理他们之间的关系。 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 Entry.objects.extra(select={'new_id': "select col from sometable where othercol > %s"}, select_params=(1,)) Entry.objects.extra(where=['headline=%s'], params=['Lennon']) Entry.objects.extra(where=["foo='a' OR bar = 'a'", "baz = 'a'"]) Entry.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） ################################################## # 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') # 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) def delete(self): # 删除 def update(self, **kwargs): # 更新 def exists(self): # 是否有结果