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" 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)