详解Django的model查询操作与查询性能优化

框架(架构)  /  管理员 发布于 7年前   338

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" LIMIT 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 21Execution 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 **kwargsobj = 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 **kwargsobj = 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 inisnull  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')  # descgroup 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.connectionfrom django.db import connection, connectionscursor = 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 .extraEntry.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。