详解Django的model查询操作与查询性能优化


						1 如何 在做ORM查询时 查看SQl的执行情况

(1) 最底层的 django.db.connection



在 django shell 中使用  python manage.py shell





>>> from django.db import connection

>>> Books.objects.all()

>>> connection.queries  ## 可以查看查询时间

[{'sql': 'SELECT "testsql_books"."id", "testsql_books"."name", "testsql_books"."author_id" FROM "testsql_books" LIMI

T 21', 'time': '0.002'}]



(2) django-extensions 插件 







pip install django-extensions







 INSTALLED_APPS = (

    ...

    'django_extensions',

    ...

    )



在 django shell 中使用  python manage.py shell_plus  --print-sql （extensions 强化）

这样每次查询都会 有sql 输出





>>> from testsql.models import Books

>>> Books.objects.all()

  SELECT "testsql_books"."id", "testsql_books"."name", "testsql_books"."author_id" FROM "testsql_books" LIMIT 21



Execution time: 0.002000s [Database: default]



<QuerySet [<Books: Books object>, <Books: Books object>, <Books: Books object>]>





2 ORM查询操作 以及优化

基本操作







增



models.Tb1.objects.create(c1='xx', c2='oo') 增加一条数据，可以接受字典类型数据 **kwargs



obj = models.Tb1(c1='xx', c2='oo')

obj.save()



 查



models.Tb1.objects.get(id=123)     # 获取单条数据，不存在则报错（不建议）

models.Tb1.objects.all()        # 获取全部

models.Tb1.objects.filter(name='seven') # 获取指定条件的数据

models.Tb1.objects.exclude(name='seven') # 获取指定条件的数据



 删



models.Tb1.objects.filter(name='seven').delete() # 删除指定条件的数据



 改

models.Tb1.objects.filter(name='seven').update(gender='0') # 将指定条件的数据更新，均支持 **kwargs

obj = models.Tb1.objects.get(id=1)

obj.c1 = '111'

obj.save()                         # 修改单条数据







查询简单操作







获取个数



  models.Tb1.objects.filter(name='seven').count()



大于，小于



  models.Tb1.objects.filter(id__gt=1)       # 获取id大于1的值

  models.Tb1.objects.filter(id__gte=1)       # 获取id大于等于1的值

  models.Tb1.objects.filter(id__lt=10)       # 获取id小于10的值

  models.Tb1.objects.filter(id__lte=10)       # 获取id小于10的值

  models.Tb1.objects.filter(id__lt=10, id__gt=1)  # 获取id大于1 且 小于10的值



in



  models.Tb1.objects.filter(id__in=[11, 22, 33])  # 获取id等于11、22、33的数据

  models.Tb1.objects.exclude(id__in=[11, 22, 33]) # not in



isnull

  Entry.objects.filter(pub_date__isnull=True)



contains



  models.Tb1.objects.filter(name__contains="ven")

  models.Tb1.objects.filter(name__icontains="ven") # icontains大小写不敏感

  models.Tb1.objects.exclude(name__icontains="ven")



range



  models.Tb1.objects.filter(id__range=[1, 2])  # 范围bettwen and



其他类似



  startswith，istartswith, endswith, iendswith,



order by



  models.Tb1.objects.filter(name='seven').order_by('id')  # asc

  models.Tb1.objects.filter(name='seven').order_by('-id')  # desc



group by--annotate



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

  models.Tb1.objects.filter(c1=1).values('id').annotate(c=Count('num'))

  SELECT "app01_tb1"."id", COUNT("app01_tb1"."num") AS "c" FROM "app01_tb1" WHERE "app01_tb1"."c1" = 1 GROUP BY "app01_tb1"."id"



limit 、offset



  models.Tb1.objects.all()[10:20]



regex正则匹配，iregex 不区分大小写



  Entry.objects.get(title__regex=r'^(An?|The) +')

  Entry.objects.get(title__iregex=r'^(an?|the) +')



date



  Entry.objects.filter(pub_date__date=datetime.date(2005, 1, 1))

  Entry.objects.filter(pub_date__date__gt=datetime.date(2005, 1, 1))



year



  Entry.objects.filter(pub_date__year=2005)

  Entry.objects.filter(pub_date__year__gte=2005)



month



  Entry.objects.filter(pub_date__month=12)

  Entry.objects.filter(pub_date__month__gte=6)



day



  Entry.objects.filter(pub_date__day=3)

  Entry.objects.filter(pub_date__day__gte=3)



week_day



  Entry.objects.filter(pub_date__week_day=2)

  Entry.objects.filter(pub_date__week_day__gte=2)



hour



  Event.objects.filter(timestamp__hour=23)

  Event.objects.filter(time__hour=5)

  Event.objects.filter(timestamp__hour__gte=12)



minute



  Event.objects.filter(timestamp__minute=29)

  Event.objects.filter(time__minute=46)

  Event.objects.filter(timestamp__minute__gte=29)



second



  Event.objects.filter(timestamp__second=31)

  Event.objects.filter(time__second=2)

  Event.objects.filter(timestamp__second__gte=31)







查询复杂操作

FK foreign key 使用的原因:





  约束

  节省硬盘



但是多表查询会降低速度，大型程序反而不使用外键，而是用单表(约束的时候，通过代码判断)

extra







  extra(self, select=None, where=None, params=None, tables=None, order_by=None, select_params=None)

    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'])





F







  from django.db.models import F

  models.Tb1.objects.update(num=F('num')+1)



Q







  方式一：

  Q(nid__gt=10)

  Q(nid=8) | Q(nid__gt=10)

  Q(Q(nid=8) | Q(nid__gt=10)) & Q(caption='root')



  方式二：

  con = Q()

  q1 = Q()

  q1.connector = 'OR'

  q1.children.append(('id', 1))

  q1.children.append(('id', 10))

  q1.children.append(('id', 9))

  q2 = Q()

  q2.connector = 'OR'

  q2.children.append(('c1', 1))

  q2.children.append(('c1', 10))

  q2.children.append(('c1', 9))

  con.add(q1, 'AND')

  con.add(q2, 'AND')



  models.Tb1.objects.filter(con)





exclude(self, *args, **kwargs)







  # 条件查询

  # 条件可以是：参数，字典，Q



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')





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 在内存中做关联，而不会再做连表查询

      # 第一次 获取所有用户表

      # 第二次 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')





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







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'])







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



下面两个 取到的是对象，并且注意 取到的对象可以 获取其他字段（这样会再去查找该字段降低性能

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





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')





执行原生SQL







1.connection

from django.db import connection, connections

cursor = connection.cursor() 

# cursor = connections['default'].cursor()

django的settings中的db配置 ' default'，指定数据库

cursor.execute("""SELECT * from auth_user where id = %s""", [1])

row = cursor.fetchone()



2 .extra

Entry.objects.extra(select={'new_id': "select id from tb where id > %s"}, select_params=(1,), order_by=['-nid'])



3 . raw     

name_map = {'a':'A','b':'B'}

models.UserInfo.objects.raw('select * from xxxx',translations=name_map)





以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持中文源码网。