Django的model查询操做 与 查询性能优化

Django的model查询操做 与 查询性能优化

1 如何 在作ORM查询时 查看SQl的执行状况

(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    ## 能够查看查询时间
[{'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查询操做 以及优化

基本操做

增

models.Tb1.objects.create(c1='xx', c2='oo')  增长一条数据，能够接受字典类型数据 **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()               # 获取所有
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

查询简单操做

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等于十一、2二、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

其余相似

    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)

查询复杂操做

FK foreign key 使用的缘由:

约束
节省硬盘

可是多表查询会下降速度，大型程序反而不使用外键，而是用单表(约束的时候，经过代码判断)

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
    # 条件能够是：参数，字典，Q

select_related(self, *fields)

性能相关：表之间进行join连表操做，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：多表连表操做时速度会慢，使用其执行屡次SQL查询  在内存中作关联，而不会再作连表查询
            # 第一次 获取全部用户表
            # 第二次 获取用户类型表where id in (用户表中的查到的全部用户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：若是存在order_by，reverse则是倒序，若是多个排序则一一倒序

下面两个 取到的是对象，而且注意 取到的对象能够 获取其余字段（这样会再去查找该字段下降性能
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)