Django ORM 操作

ORM查询操作及优化

基本操作

最底层的 django.db.connection

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'}]

django-extensions 插件

1. 下载插件

pip install django-extensions

2. 添加到中间项中

INSTALLED_APPS = (
    ...
    'django_extensions',
    ...
    )

3. 在 django shell 中使用

python manage.py shell_plus  --print-sql （extensions 强化）

4. 每次查询都会打印出相关语句

增删改查

• 增

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

• 批量添加

from django.db import transaction
transaction.set_autocommit(False)
try:
    User.objects.bulk_create([User(i) for i in range(10)])
except Exception e:
    transaction.rollback()
    raise e
else:
    transaction.commit()
finally:
    transaction.set_autocommit(True)

• 删

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

• 查

# 获取单条数据，不存在则报错（不建议）
models.Tb1.objects.get(id=123)
# 获取全部
models.Tb1.objects.all()
# 获取指定条件的数据
models.Tb1.objects.filter(name='seven')
# 获取指定条件的数据
models.Tb1.objects.exclude(name='seven')

• 改

# 将指定条件的数据更新，均支持 **kwargs
models.Tb1.objects.filter(name='seven').update(gender='0')  
obj = models.Tb1.objects.get(id=1)
obj.c1 = '111'
# 修改单条数据
obj.save()

查询简单操作

• 获取个数

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

• 大于，小于

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

• in

# 获取id等于11、22、33的数据
models.Tb1.objects.filter(id__in=[11, 22, 33])
# not in
models.Tb1.objects.exclude(id__in=[11, 22, 33])

• isnull

Entry.objects.filter(pub_date__isnull=True)

• contains

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

• 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) +')

• range

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

• distinct

# 去重
Entity.objects.filter(...).distinct()

其他类似
startswith，istartswith, endswith, iendswith,

• order by

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

• group by

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]

• date

# 等于
Entry.objects.filter(pub_date__date=datetime.date(2005, 1, 1))
# 大于
Entry.objects.filter(pub_date__date__gt=datetime.date(2005, 1, 1))
# 大于等于
Entry.objects.filter(pub_date__date__gte=datetime.date(2005, 1, 1))
# 小于
Entry.objects.filter(pub_date__date__lt=datetime.date(2005, 1, 1))
# 小于等于
Entry.objects.filter(pub_date__date__lte=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

懒惰加载

# 懒惰加载
users = User.objects.all().defer('note')
for user in users:
    print(user.note)

# 只获取一个字段
users = User.objects.all().only('note')
for user in users:
    print(user.note)

# 关联表的查询，解决N+1查询 针对一对多
users = User.objects.all().select_related('role')
for user in users:
    print(user.role)
# 关联表的查询，解决N+1查询，针对多对多
users = User.objects.all().prefetch_related('permission')
for user in users:
    print(user.=permission)

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

# ps
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)

# 进行列的运算操作
from django.db.models import Q
models.Tb1.objects.values("name").annotate(sum_data= Sum(F("cnt") * F("money")))

Q

 方式一：
Q(nid__gt=10)
Q(nid=8) | 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
models.UserInfo.objects.values("age").annotate(cnt=Count("name", distinct=True))

aggregate(self, *args, **kwargs)

聚合操作，是QuerySet的一个终端自居，使用后返回“名称-值”的字典

from django.db.models import Count, Avg, Max, Min, Sum
Book.objects.aggregate(Avg('price'), Max('price'), Min('price'))

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')

values(self, *fields)

models.UserInfo.objects.values("name", "id")

执行原生SQL

1. connection

from django.db import connection
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)

查看ORM生成的sql

queryset = User.objects.all()
print(queryset.query)

####### 
from django.db import connection
for query in connection.queries:
    print(query)

DB->model

python manage.py inspectdb
python manage.py inspectdb > models.py