所有ORM操作 (第二版)
#######################################################################
# 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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