Django ORM执行原生SQL
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# extra
# 在QuerySet的基础上继续执行子语句
# extra(self, select=None, where=None, params=None, tables=None, order_by=None, select_params=None)
# select和select_params是一组，where和params是一组，tables用来设置from哪个表
# 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'])
举个例子：
models.UserInfo.objects.extra(
select
=
{
'newid'
:
'select count(1) from app01_usertype where id>%s'
},
select_params
=
[
1
,],
where
=
[
'age>%s'
],
params
=
[
18
,],
order_by
=
[
'-age'
],
tables
=
[
'app01_usertype'
]
)
"""
select
app01_userinfo.id,
(select count(1) from app01_usertype where id>1) as newid
from app01_userinfo,app01_usertype
where
app01_userinfo.age > 18
order by
app01_userinfo.age desc
"""
# 执行原生SQL
# 更高灵活度的方式执行原生SQL语句
# from django.db import connection, connections
# cursor = connection.cursor() # cursor = connections['default'].cursor()
# cursor.execute("""SELECT * from auth_user where id = %s""", [1])
# row = cursor.fetchone()
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QuerySet方法大全
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##################################################################
# PUBLIC METHODS THAT ALTER ATTRIBUTES AND RETURN A NEW QUERYSET #
##################################################################
def
all
(
self
)
# 获取所有的数据对象
def
filter
(
self
,
*
args,
*
*
kwargs)
# 条件查询
# 条件可以是：参数，字典，Q
def
exclude(
self
,
*
args,
*
*
kwargs)
# 条件查询
# 条件可以是：参数，字典，Q
def
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。
总结：
1.
select_related主要针一对一和多对一关系进行优化。
2.
select_related使用SQL的JOIN语句进行优化，通过减少SQL查询的次数来进行优化、提高性能。
def
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Python代码中实现连表操作。
总结：
1.
对于多对多字段（ManyToManyField）和一对多字段，可以使用prefetch_related()来进行优化。
2.
prefetch_related()的优化方式是分别查询每个表，然后用Python处理他们之间的关系。
def
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
def
distinct(
self
,
*
field_names)
# 用于distinct去重
models.UserInfo.objects.values(
'nid'
).distinct()
# select distinct nid from userinfo
注：只有在PostgreSQL中才能使用distinct进行去重
def
order_by(
self
,
*
field_names)
# 用于排序
models.UserInfo.objects.
all
().order_by(
'-id'
,
'age'
)
def
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'
])
def
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
def
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
def
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'
)
def
using(
self
, alias):
指定使用的数据库，参数为别名（setting中的设置）
##################################################
# PUBLIC METHODS THAT RETURN A QUERYSET SUBCLASS #
##################################################
def
raw(
self
, raw_query, params
=
None
, translations
=
None
, using
=
None
):
# 执行原生SQL
models.UserInfo.objects.raw(
'select * from userinfo'
)
# 如果SQL是其他表时，必须将名字设置为当前UserInfo对象的主键列名
models.UserInfo.objects.raw(
'select id as nid from 其他表'
)
# 为原生SQL设置参数
models.UserInfo.objects.raw(
'select id as nid from userinfo where nid>%s'
, params
=
[
12
,])
# 将获取的到列名转换为指定列名
name_map
=
{
'first'
:
'first_name'
,
'last'
:
'last_name'
,
'bd'
:
'birth_date'
,
'pk'
:
'id'
}
Person.objects.raw(
'SELECT * FROM some_other_table'
, translations
=
name_map)
# 指定数据库
models.UserInfo.objects.raw(
'select * from userinfo'
, using
=
"default"
)
################### 原生SQL ###################
from
django.db
import
connection, connections
cursor
=
connection.cursor()
# cursor = connections['default'].cursor()
cursor.execute(
"""SELECT * from auth_user where id = %s"""
, [
1
])
row
=
cursor.fetchone()
# fetchall()/fetchmany(..)
def
values(
self
,
*
fields):
# 获取每行数据为字典格式
def
values_list(
self
,
*
fields,
*
*
kwargs):
# 获取每行数据为元祖
def
dates(
self
, field_name, kind, order
=
'ASC'
):
# 根据时间进行某一部分进行去重查找并截取指定内容
# kind只能是："year"（年）, "month"（年-月）, "day"（年-月-日）
# order只能是："ASC" "DESC"
# 并获取转换后的时间
-
year : 年
-
01
-
01
-
month: 年
-
月
-
01
-
day : 年
-
月
-
日
models.DatePlus.objects.dates(
'ctime'
,
'day'
,
'DESC'
)
def
datetimes(
self
, field_name, kind, order
=
'ASC'
, tzinfo
=
None
):
# 根据时间进行某一部分进行去重查找并截取指定内容，将时间转换为指定时区时间
# kind只能是 "year", "month", "day", "hour", "minute", "second"
# order只能是："ASC" "DESC"
# tzinfo时区对象
models.DDD.objects.datetimes(
'ctime'
,
'hour'
,tzinfo
=
pytz.UTC)
models.DDD.objects.datetimes(
'ctime'
,
'hour'
,tzinfo
=
pytz.timezone(
'Asia/Shanghai'
))
"""
pip3 install pytz
import pytz
pytz.all_timezones
pytz.timezone(‘Asia/Shanghai’)
"""
def
none(
self
):
# 空QuerySet对象
####################################
# METHODS THAT DO DATABASE QUERIES #
####################################
def
aggregate(
self
,
*
args,
*
*
kwargs):
# 聚合函数，获取字典类型聚合结果
from
django.db.models
import
Count, Avg,
Max
,
Min
,
Sum
result
=
models.UserInfo.objects.aggregate(k
=
Count(
'u_id'
, distinct
=
True
), n
=
Count(
'nid'
))
=
=
=
> {
'k'
:
3
,
'n'
:
4
}
def
count(
self
):
# 获取个数
def
get(
self
,
*
args,
*
*
kwargs):
# 获取单个对象
def
create(
self
,
*
*
kwargs):
# 创建对象
def
bulk_create(
self
, objs, batch_size
=
None
):
# 批量插入
# batch_size表示一次插入的个数
objs
=
[
models.DDD(name
=
'r11'
),
models.DDD(name
=
'r22'
)
]
models.DDD.objects.bulk_create(objs,
10
)
def
get_or_create(
self
, defaults
=
None
,
*
*
kwargs):
# 如果存在，则获取，否则，创建
# defaults 指定创建时，其他字段的值
obj, created
=
models.UserInfo.objects.get_or_create(username
=
'root1'
, defaults
=
{
'email'
:
'1111111'
,
'u_id'
:
2
,
't_id'
:
2
})
def
update_or_create(
self
, defaults
=
None
,
*
*
kwargs):
# 如果存在，则更新，否则，创建
# defaults 指定创建时或更新时的其他字段
obj, created
=
models.UserInfo.objects.update_or_create(username
=
'root1'
, defaults
=
{
'email'
:
'1111111'
,
'u_id'
:
2
,
't_id'
:
1
})
def
first(
self
):
# 获取第一个
def
last(
self
):
# 获取最后一个
def
in_bulk(
self
, id_list
=
None
):
# 根据主键ID进行查找
id_list
=
[
11
,
21
,
31
]
models.DDD.objects.in_bulk(id_list)
def
delete(
self
):
# 删除
def
update(
self
,
*
*
kwargs):
# 更新
def
exists(
self
):
# 是否有结果
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Django终端打印SQL语句
在Django项目的settings.py文件中，在最后复制粘贴如下代码：即为你的Django项目配置上一个名为django.db.backends的logger实例即可查看翻译后的SQL语句。
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LOGGING
=
{
'version'
:
1
,
'disable_existing_loggers'
:
False
,
'handlers'
: {
'console'
:{
'level'
:
'DEBUG'
,
'class'
:
'logging.StreamHandler'
,
},
},
'loggers'
: {
'django.db.backends'
: {
'handlers'
: [
'console'
],
'propagate'
:
True
,
'level'
:
'DEBUG'
,
},
}
}
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在Python脚本中调用Django环境
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import
os
if
__name__
=
=
'__main__'
:
os.environ.setdefault(
"DJANGO_SETTINGS_MODULE"
,
"BMS.settings"
)
import
django
django.setup()
from
app01
import
models
books
=
models.Book.objects.
all
()
print
(books)
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