SQLAlchemy-对象关系教程ORM-query

一：对象关系教程查询

　　一个

 Query

Session的

　　Query返回的是元组，可以像普通Python对象一样，元组返回一个属性的名字或者一个类的类名

　　1)

Query

User

for instance in session.query(User).order_by(User.id):
print(instance.name,instance.fullname)

----------------------------------------------------------------
ed tianshi
shi shi jone
san san jone
jun jun jone

　　2)ORM-instrumented描述符作为参数　

for name,fullname in session.query(User.name,User.fullname):
print(name,fullname)
----------------------------------------------------------------
ed tianshi
shi shi jone
san san jone
jun jun jone

 　　3)

元组返回一个属性的名字或者一个类的类名

for row in session.query(User,User.name).all():
print(row.User,row.name)
----------------------------------------------------------
name:ed full name:tianshi password:123456 ed
name:shi full name:shi jone password:123456 shi
name:san full name:san jone password:123456 san
name:jun full name:jun jone password:123456 jun

　　4) 通过label()返回属性列重命名

for row in session.query(User.name.label("new_name")).all():
print(row.new_name)
--------------------------------------------------------------------------
ed
shi
san
jun

　　5)通过

aliased()

from sqlalchemy.orm import aliased
user_alias=aliased(User,name="user_alias") #把类实例重命名为user_alias

for row in session.query(user_alias,user_alias.name).all():
print(row.user_alias)
--------------------------------------
name:ed full name:tianshi password:123456
name:shi full name:shi jone password:123456
name:san full name:san jone password:123456
name:jun full name:jun jone password:123456

 　　6）

Query

for u in session.query(User).order_by(User.id)[1:3]:

表示从第1条后面开始查询2条 不包括3

print(u.id)
-----------------------------------------
2 
3

　　7）query查询结果过滤filter_by()和filter()。filter可以支持更多查询条件，注意写法上不同。

#filter_by查询
for name, in session.query(User.name).filter_by(fullname="shi jun2"):
print(name)
#filter查询
for name,in session.query(User.name).filter(User.fullname=="shi jun2"):
print(name)
#filter复合查询，这里相当于and查询
for user in session.query(User).filter(User.name=='shi2').filter(User.fullname=='shi jun2'):
print(user)

结果：
shi2
shi2
User<name:shi2 fullname:shi jun2 password:123456>

二：filter常用操作

1) equals

query.filter(User.name == 'ed')

2) not equals

query.filter(User.name != 'ed')

3) LIKE 是区分大小写的

query.filter(User.name.like('%ed%'))

4) ILIKE 不区分大小写的

query.filter(User.name.ilike('%ed%'))

5) IN

query.filter(User.name.in_(['ed', 'wendy', 'jack']))

# works with query objects too:
query.filter(User.name.in_(
session.query(User.name).filter(User.name.like('%ed%'))
))

6) NOT IN

query.filter(~User.name.in_(['ed', 'wendy', 'jack']))

7) IS NULL

query.filter(User.name == None)
query.filter(User.name.is_(None))

8)IS NOT NULL

query.filter(User.name != None)
query.filter(User.name.isnot(None))

9) AND

# use and_()
from sqlalchemy import and_
query.filter(and_(User.name == 'ed', User.fullname == 'Ed Jones'))

# or send multiple expressions to .filter()
query.filter(User.name == 'ed', User.fullname == 'Ed Jones')

# or chain multiple filter().filter_by() calls
query.filter(User.name == 'ed').filter(User.fullname == 'Ed Jones')

10) OR

from sqlalchemy import or_
query.filter(or_(User.name == 'ed', User.name == 'wendy'))

11)MATCH

match()使用一个特定于数据库的 MATCH或 CONTAINS函数;它的行为会有所不同后端和不可用等后端SQLite。
query.filter(User.name.match('wendy'))

三:返回结果

　　Query发出SQL语句和返回包括数据库结果一个值

print(session.query(User.name).filter(User.fullname=="shi jun2"))
--------------------------------------------
SELECT users.name AS users_name
FROM users
WHERE users.fullname = %(fullname_1)s

 　  1）all()取出所的记录

　　2）first()返回第一条记录

　　3）one():不存在，或者有多行记录的时候报错（no items found，multiple items found

　　4）one_or_none()：如果有一条记录就返回一条记录，如果没有记录就返回NONE

　　5）scalar()调用 one()方法,成功返回只有一行结果的第1列

query=session.query(User.name).first()
print(query)
('shi',)
query=session.query(User.name).all()
print(query)
[('shi',), ('shi2',)]
query=session.query(User.name).one()
print(query)

sqlalchemy.orm.exc.MultipleResultsFound: Multiple rows were found for one()

query=session.query(User.name).filter(User.name=="shi").one()#这里查询出的结果只有1条，所以不会报错
print(query)
('shi',)
如果有一条记录就返回一条记录，如果没有记录就返回NONE
query=session.query(User.name).filter(User.name=="shi").one_or_none()
('shi',)
print(query)
query=session.query(User.name).filter(User.name=="sh3").one_or_none()
print(query)
None

query=session.query(User.name).filter(User.name=="shi").scalar()
print(query)
shi

四：Query通过text()可以使用字符串

# for user in session.query(User).filter(text("id<224")).order_by(text("id")).all():
#     print(user)

#通过params传递参数,使用:来分开参数

# for user in session.query(User).filter(text("id>:value and name=:name")).params(value=1,name="fred").order_by(User.id).one():
#     print(user)

for user in session.query(User).from_statement(text("select * from users where name=:name")).params(name="shi").all():
print(user)

五：count()方法用于确定SQL语句将返回多少行

print(session.query(User).filter(User.name.like("shi%")).count())
使用func.count()统计

from sqlalchemy import func
for row in session.query(func.count(User.name),User.name).group_by(User.name).all():
print(row)
－－－－－－－－－－－－
(1, 'shi')
(1, 'shi2')

select count(*) from table
==session.query(func.count('*')).select_from(User).scalar()