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Django一些鮮為人知的操作

... 批量 相關 ram esql 一對多 ali 一對一 plus

目錄:

  - Django ORM執行原生SQL

  - QuerySet方法大全

一、Django ORM執行原生SQL

# extra
# 在QuerySet的基礎上繼續執行子語句
# extra(self, select=None, where=None, params=None, tables=None, order_by=None, select_params=None)

# select和select_params是一組,where和params是一組,tables用來設置from哪個表
# 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‘]) 舉個例子: 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 """ # 執行原生SQL # 更高靈活度的方式執行原生SQL語句 # 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()

二、QuerySet方法大全

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

def all(self)
    # 獲取所有的數據對象

def filter(self, *args, **kwargs)
    # 條件查詢
    # 條件可以是:參數,字典,Q

def exclude(self, *args, **kwargs)
    # 條件查詢
    # 條件可以是:參數,字典,Q

def select_related(self, *fields)
    性能相關:表之間進行join連表操作,一次性獲取關聯的數據。

    總結:
    1. select_related主要針一對一和多對一關系進行優化。
    2. select_related使用SQL的JOIN語句進行優化,通過減少SQL查詢的次數來進行優化、提高性能。

def prefetch_related(self, *lookups)
    性能相關:多表連表操作時速度會慢,使用其執行多次SQL查詢在Python代碼中實現連表操作。

    總結:
    1. 對於多對多字段(ManyToManyField)和一對多字段,可以使用prefetch_related()來進行優化。
    2. prefetch_related()的優化方式是分別查詢每個表,然後用Python處理他們之間的關系。

def annotate(self, *args, **kwargs)
    # 用於實現聚合group by查詢

    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)
    # 用於distinct去重
    models.UserInfo.objects.values(nid).distinct()
    # select distinct nid from userinfo

    註:只有在PostgreSQL中才能使用distinct進行去重

def order_by(self, *field_names)
    # 用於排序
    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)
    # 構造額外的查詢條件或者映射,如:子查詢

    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()
    # 註:如果存在order_by,reverse則是倒序,如果多個排序則一一倒序


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

 def only(self, *fields):
    #僅取某個表中的數據
     models.UserInfo.objects.only(username,id)
     或
     models.UserInfo.objects.filter(...).only(username,id)

 def using(self, alias):
     指定使用的數據庫,參數為別名(setting中的設置)


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

def raw(self, raw_query, params=None, translations=None, using=None):
    # 執行原生SQL
    models.UserInfo.objects.raw(select * from userinfo)

    # 如果SQL是其他表時,必須將名字設置為當前UserInfo對象的主鍵列名
    models.UserInfo.objects.raw(select id as nid from 其他表)

    # 為原生SQL設置參數
    models.UserInfo.objects.raw(select id as nid from userinfo where nid>%s, params=[12,])

    # 將獲取的到列名轉換為指定列名
    name_map = {first: first_name, last: last_name, bd: birth_date, pk: id}
    Person.objects.raw(SELECT * FROM some_other_table, translations=name_map)

    # 指定數據庫
    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):
    # 獲取每行數據為字典格式

def values_list(self, *fields, **kwargs):
    # 獲取每行數據為元祖

def dates(self, field_name, kind, order=ASC):
    # 根據時間進行某一部分進行去重查找並截取指定內容
    # kind只能是:"year"(年), "month"(年-月), "day"(年-月-日)
    # order只能是:"ASC"  "DESC"
    # 並獲取轉換後的時間
        - 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):
    # 根據時間進行某一部分進行去重查找並截取指定內容,將時間轉換為指定時區時間
    # kind只能是 "year", "month", "day", "hour", "minute", "second"
    # order只能是:"ASC"  "DESC"
    # tzinfo時區對象
    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對象


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

def aggregate(self, *args, **kwargs):
   # 聚合函數,獲取字典類型聚合結果
   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):
   # 獲取個數

def get(self, *args, **kwargs):
   # 獲取單個對象

def create(self, **kwargs):
   # 創建對象

def bulk_create(self, objs, batch_size=None):
    # 批量插入
    # batch_size表示一次插入的個數
    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,則獲取,否則,創建
    # defaults 指定創建時,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,則更新,否則,創建
    # defaults 指定創建時或更新時的其他字段
    obj, created = models.UserInfo.objects.update_or_create(username=root1, defaults={email: 1111111,u_id: 2, t_id: 1})

def first(self):
   # 獲取第一個

def last(self):
   # 獲取最後一個

def in_bulk(self, id_list=None):
   # 根據主鍵ID進行查找
   id_list = [11,21,31]
   models.DDD.objects.in_bulk(id_list)

def delete(self):
   # 刪除

def update(self, **kwargs):
    # 更新

def exists(self):
   # 是否有結果

Django一些鮮為人知的操作