django-orm进阶操作
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-
- 进阶操作
- 高级操作
- QuerySet高级操作
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进阶操作
# 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 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') # desc
# 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]
# 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)
进阶操作高级操作
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-select_params
tmp = models.Book.objects.all().extra(select={"n":"select count(1) from app05_book"})
for i in tmp:
print(i.title, i.n)
书一 6
书二 6
书三(第) 6
书四(第) 6
书五(第) 6
书六(第) 6select占位符
tmp = models.Book.objects.all().extra(select={"n":"select count(1) from app05_book WHERE id>%s"},select_params=[3,])
for i in tmp:
print(i.title, i.n)
书一 3
书二 3
书三(第) 3
书四(第) 3
书五(第) 3
书六(第) 3where-params
models.Book.objects.extra(where=["title=%s"],params=["书一"])
]> models.Book.objects.extra(where=["title='书一' or title='书二'"])
, ]> and关系
models.Book.objects.extra(where=["title='书一'","id=2"])
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()QuerySet高级操作
去重
def distinct(self, *field_names)
models.Book.objects.values("title").distinct()
<QuerySet [{'title': '书一'}, {'title': '书三(第)'}, {'title': '书四(第)'}, {'title': '书五(第)'}, {'title': '书六(第)'}]>select_related实现表之间进行一对一和多对一优化
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。实例代码如下：
tmp = models.Book.objects.all()
for i in tmp:
print(i.publisher.name)
沙河出版社
沙河出版社
三里屯
五道口
国贸
五道口
a2 = models.Book.objects.all().select_related("publisher")
for i in a2:
print(i.publisher.name)
沙河出版社
沙河出版社
五道口
五道口
三里屯
国贸以上代码中第一种查询方式会查询数据库六次，第二种方式会查询数据库次数为1次
prefetch_related实现表之间进行一对多和多对多优化
只能正向查询~且不能跨表
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。实例代码如下：
tmp = models.Author.objects.all().prefetch_related("books")
for i in tmp:
print(i.books.all())
, ]>
, ]>
]>
defer
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实例代码如下：
a = models.Author.objects.all().defer("name")
for i in a:
print(i)
小一
小二
小三
小四
a = models.Author.objects.all().defer("name").values()
for i in a:
print(i)
{'id': 1, 'name': '小一', 'author_detail_id': 1}
{'id': 2, 'name': '小二', 'author_detail_id': 2}
{'id': 3, 'name': '小三', 'author_detail_id': 3}
{'id': 4, 'name': '小四', 'author_detail_id': 4}
a = models.Author.objects.all().defer(“name”).values()
虽然在查询中排除name字段，但是在循环中如果要输出关于name的信息，那么依然会继续查询输出name
only
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')示例代码如下：
a = models.Author.objects.only("name")
for i in a:
print(i)
小一
小二
小三
小四raw执行原生SQL
执行原生SQL
tmp = models.Author.objects.raw("select * from app05_author")
for i in tmp:
print(i.name)
小一
小二
小三
小四为原生SQL设置参数
a = models.Book.objects.raw("select id from app05_book WHERE id>%s",params=[3,])
for i in a:
print(i)
书四(第)
书五(第)
书六(第)dates
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')示例代码如下：
models.Book.objects.all().dates("publish_day","year","DESC")
.date(2018, 1, 1), datetime.date(2017, 1, 1)]>
models.Book.objects.all().dates("publish_day","month","DESC")
.date(2018, 4, 1), datetime.date(2018, 1, 1), datetime.date(2017, 1, 1)]>
models.Book.objects.all().dates("publish_day","day","DESC")
.date(2018, 4, 12), datetime.date(2018, 1, 29), datetime.date(2018, 1, 25), datetime.date(2018, 1, 19), datetime.date(2018, 1, 11), datetime.date(2017, 1, 18)]>
datetimes
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’)
"""
bulk_create
参数为一次性插入的个数
objs = [models.Publisher(name="aaa",addr="aaa"),models.Publisher(name="bbb",addr="bbb")]
models.Publisher.objects.bulk_create(objs,2)
[, ]
get_or_create
# 如果存在，则获取，否则，创建
# defaults 指定创建时，其他字段的值
models.Publisher.objects.get_or_create(name="沙河出版社")
(, False)
models.Publisher.objects.get_or_create(name="沙河出版社1")
(1>, True)
models.Publisher.objects.get_or_create(name="沙河出版1",addr="sss")
(1>, True)
models.Publisher.objects.get_or_create(name="沙河版1",defaults={"addr":"sdfsdsf"})
(1>, True) 
update_or_create
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})
in_bulk
# 根据主键ID进行查找
id_list = [11,21,31]
models.DDD.objects.in_bulk(id_list)
from app05 import models
models.Book.objects.in_bulk([1,2,3])
(0.000) SELECT @@SQL_AUTO_IS_NULL; args=None
(0.001) SELECT VERSION(); args=None
(0.002) SELECT `app05_book`.`id`, `app05_book`.`title`, `app05_book`.`price`, `app05_book`.`publish_day`, `app05_book`.`publisher_id` FROM `app05_book` WHERE `app05_book`.`id` IN (1, 2, 3); args=(1, 2, 3)
{1: , 2: , 3: 书三(第)>}