SQLAlchemy

SQLAlchemy
**1.介绍 **
SQLAlchemy是一个基于Python实现的ORM框架。该框架建立在
DB API之上，使用关系对象映射进行数据库操作，简言之便是：将 类和对象转换成SQL，然后使用数据API执行SQL并获取执行结果。 组成部分： SQLAlchemy本身无法操作数据库，其必须以来pymsql等第三方插件，Dialect用于和数据API进行交流，根据配置文件的不同调用不 同的数据库API，从而实现对数据库的操作，如： django中如何反向生成models
2.简单使用（能创建表，删除表，不能修改表）
修改表：在数据库添加字段，类对应上 1执行原生sql（不常用）
pip3 install sqlalchemy Copy
Engine，框架的引擎
Connection Pooling ，数据库连接池
Dialect，选择连接数据库的DB API种类
Schema/Types，架构和类型
SQL Exprression Language，SQL表达式语言
Copy
MySQL-Python
mysql+mysqldb://:@[:]/
pymysql
mysql+pymysql://:@/[?]
MySQL-Connector
mysql+mysqlconnector://:@[:]/
cx_Oracle
oracle+cx_oracle://user:pass@host:port/dbname[?key=value&key=value...]
更多：http://docs.sqlalchemy.org/en/latest/dialects/index.html
Copy
python manage.py inspectdb > app/models.py Copy
import time
import threading
import sqlalchemy
from sqlalchemy import create_engine
from sqlalchemy.engine.base import Engine
engine = create_engine(
"mysql+pymysql://root:123456@127.0.0.1:3306/test?charset=utf8",
max_overflow=0, # 超过连接池大小外最多创建的连接
pool_size=5, # 连接池大小
pool_timeout=30, # 池中没有线程最多等待的时间，否则报错
pool_recycle=-1 # 多久之后对线程池中的线程进行一次连接的回收（重置） )
def task(arg):
conn = engine.raw_connection()
cursor = conn.cursor()
cursor.execute(
"select * from app01_book"
)
result = cursor.fetchall()
print(result)
cursor.close()
conn.close()
for i in range(20):
t = threading.Thread(target=task, args=(i,))
t.start()
import datetime
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, Text, ForeignKey, DateTime, UniqueConstraint, Index
Base = declarative_base()
class Users(Base):
tablename = 'users' # 数据库表名称
id = Column(Integer, primary_key=True) # id 主键
name = Column(String(32), index=True, nullable=False) # name列，索引，不可为空

email = Column(String(32), unique=True)

datetime.datetime.now不能加括号，加了括号，以后永远是当前时间

ctime = Column(DateTime, default=datetime.datetime.now)

extra = Column(Text, nullable=True)

table_args = (

UniqueConstraint('id', 'name', name='uix_id_name'), #联合唯一

Index('ix_id_name', 'name', 'email'), #索引

)
def init_db():
"""
根据类创建数据库表
:return:
"""
engine = create_engine(
"mysql+pymysql://root:123456@127.0.0.1:3306/aaa?charset=utf8",
max_overflow=0, # 超过连接池大小外最多创建的连接
pool_size=5, # 连接池大小
pool_timeout=30, # 池中没有线程最多等待的时间，否则报错
pool_recycle=-1 # 多久之后对线程池中的线程进行一次连接的回收（重置）
)
Base.metadata.create_all(engine)
def drop_db():
"""
根据类删除数据库表
:return:
"""
engine = create_engine(
"mysql+pymysql://root:123456@127.0.0.1:3306/aaa?charset=utf8",
max_overflow=0, # 超过连接池大小外最多创建的连接
pool_size=5, # 连接池大小
pool_timeout=30, # 池中没有线程最多等待的时间，否则报错
pool_recycle=-1 # 多久之后对线程池中的线程进行一次连接的回收（重置）
)
Base.metadata.drop_all(engine)

3.一对多关系
4.多对多关系
if name == 'main':

drop_db()

init_db()
from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
from models import Users

"mysql+pymysql://root@127.0.0.1:3306/aaa"

engine = create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/aaa", max_overflow=0, pool_size=5)
Connection = sessionmaker(bind=engine)

每次执行数据库操作时，都需要创建一个Connection

con = Connection()

############# 执行ORM操作

obj1 = Users(name="lqz")
con.add(obj1)

提交事务

con.commit()

关闭session，其实是将连接放回连接池

con.close()
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class Hobby(Base):
tablename = 'hobby'
id = Column(Integer, primary_key=True)
caption = Column(String(50), default='篮球')
class Person(Base):
tablename = 'person'
nid = Column(Integer, primary_key=True)
name = Column(String(32), index=True, nullable=True)

hobby指的是tablename而不是类名，uselist=False

hobby_id = Column(Integer, ForeignKey("hobby.id"))

跟数据库无关，不会新增字段，只用于快速链表操作

类名，backref用于反向查询

hobby=relationship('Hobby',backref='pers')
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class Boy2Girl(Base):
tablename = 'boy2girl'
id = Column(Integer, primary_key=True, autoincrement=True)
girl_id = Column(Integer, ForeignKey('girl.id'))
boy_id = Column(Integer, ForeignKey('boy.id'))
class Girl(Base):
tablename = 'girl'
id = Column(Integer, primary_key=True)
name = Column(String(64), unique=True, nullable=False)
class Boy(Base):
tablename = 'boy'
id = Column(Integer, primary_key=True, autoincrement=True)
hostname = Column(String(64), unique=True, nullable=False)
5.操作数据表
**6.基于scoped_session实现线程安全 **
7.基本增删查改

与生成表结构无关，仅用于查询方便,放在哪个单表中都可以

servers = relationship('Girl', secondary='boy2girl', backref='boys')
from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
from models import Users
engine = create_engine("mysql+pymysql://root:123456@127.0.0.1:3306/aaa", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)

每次执行数据库操作时，都需要创建一个session

session = Session()

############# 执行ORM操作

obj1 = Users(name="lqz")
session.add(obj1)

提交事务

session.commit()

关闭session

session.close()
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from sqlalchemy.orm import sessionmaker
from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session
from models import Users
engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)
"""

线程安全，基于本地线程实现每个线程用同一个session

特殊的：scoped_session中有原来方法的Session中的一下方法：

public_methods = (
'contains', 'iter', 'add', 'add_all', 'begin', 'begin_nested',
'close', 'commit', 'connection', 'delete', 'execute', 'expire',
'expire_all', 'expunge', 'expunge_all', 'flush', 'get_bind',
'is_modified', 'bulk_save_objects', 'bulk_insert_mappings',
'bulk_update_mappings',
'merge', 'query', 'refresh', 'rollback',
'scalar'
)
"""

scoped_session类并没有继承Session,但是却又它的所有方法

session = scoped_session(Session)

############# 执行ORM操作

obj1 = Users(name="alex1")
session.add(obj1)

提交事务

session.commit()

关闭session

session.close()
Copy
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2020/9/8 09-02
SQLAlchemy
-
小猿取经
-
博客园
https://www.cnblogs.com/xiaoyuanqujing/protected/articles/11715497.html 5/11
8.常用操作
import time
import threading
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy import create_engine
from sqlalchemy.sql import text
from db import Users, Hosts
engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)
session = Session()

################ 添加

"""
obj1 = Users(name="wupeiqi")
session.add(obj1)
session.add_all([
Users(name="lqz"),
Users(name="egon"),
Hosts(name="c1.com"),
])
session.commit()
"""

################ 删除

"""
session.query(Users).filter(Users.id > 2).delete()
session.commit()
"""

################ 修改

"""

传字典

session.query(Users).filter(Users.id > 0).update({"name" : "lqz"})

类似于django的F查询

session.query(Users).filter(Users.id > 0).update({Users.name: Users.name + "099"}, synchronize_session=False)
session.query(Users).filter(Users.id > 0).update({"age": Users.age + 1}, synchronize_session="evaluate")
session.commit()
"""

################ 查询

"""
r1 = session.query(Users).all()

只取age列，把name重命名为xx

r2 = session.query(Users.name.label('xx'), Users.age).all()

filter传的是表达式，filter_by传的是参数

r3 = session.query(Users).filter(Users.name == "lqz").all()
r4 = session.query(Users).filter_by(name='lqz').all()
r5 = session.query(Users).filter_by(name='lqz').first()

:value 和:name 相当于占位符，用params传参数

r6 = session.query(Users).filter(text("id<:value and name=:name")).params(value=224, name='fred').order_by(Us

自定义查询sql

r7 = session.query(Users).from_statement(text("SELECT * FROM users where name=:name")).params(name='ed').all(
"""

增，删，改都要commit()

session.close()
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条件

ret = session.query(Users).filter_by(name='lqz').all()
ret = session.query(Users).filter(Users.id > 1, Users.name == 'eric').all()
ret = session.query(Users).filter(Users.id.between(1, 3), Users.name == 'eric').all()

注意下划线

ret = session.query(Users).filter(Users.id.in_([1,3,4])).all()

~非，除。。外

ret = session.query(Users).filter(~Users.id.in_([1,3,4])).all()

二次筛选

ret = session.query(Users).filter(Users.id.in_(session.query(Users.id).filter_by(name='eric'))).all()
from sqlalchemy import and_, or_

or_包裹的都是or条件，and_包裹的都是and条件

ret = session.query(Users).filter(and_(Users.id > 3, Users.name == 'eric')).all()
ret = session.query(Users).filter(or_(Users.id < 2, Users.name == 'eric')).all()
ret = session.query(Users).filter(
or_(
Users.id < 2,
and_(Users.name == 'eric', Users.id > 3),
Users.extra != ""
)).all()

通配符，以e开头，不以e开头

ret = session.query(Users).filter(Users.name.like('e%')).all()
ret = session.query(Users).filter(~Users.name.like('e%')).all()

限制，用于分页，区间

ret = session.query(Users)[1:2]

排序，根据name降序排列（从大到小）

ret = session.query(Users).order_by(Users.name.desc()).all()

第一个条件重复后，再按第二个条件升序排

ret = session.query(Users).order_by(Users.name.desc(), Users.id.asc()).all()

分组

from sqlalchemy.sql import func
ret = session.query(Users).group_by(Users.extra).all()

分组之后取最大id，id之和，最小id

ret = session.query(
func.max(Users.id),
func.sum(Users.id),
func.min(Users.id)).group_by(Users.name).all()

haviing筛选

ret = session.query(
func.max(Users.id),
func.sum(Users.id),
func.min(Users.id)).group_by(Users.name).having(func.min(Users.id) >2).all()

连表（默认用forinkey关联）

ret = session.query(Users, Favor).filter(Users.id == Favor.nid).all()

join表，默认是inner join

ret = session.query(Person).join(Favor).all()

isouter=True 外连，表示Person left join Favor，没有右连接，反过来即可

ret = session.query(Person).join(Favor, isouter=True).all()

打印原生sql

aa=session.query(Person).join(Favor, isouter=True)
print(aa)

自己指定on条件（连表条件）,第二个参数，支持on多个条件，用and_,同上

ret = session.query(Person).join(Favor,Person.id==Favor.id, isouter=True).all()

组合（了解）UNION 操作符用于合并两个或多个 SELECT 语句的结果集

union和union all的区别？

q1 = session.query(Users.name).filter(Users.id > 2)
q2 = session.query(Favor.caption).filter(Favor.nid < 2)
ret = q1.union(q2).all()
q1 = session.query(Users.name).filter(Users.id > 2)
9.执行原生sql
10.一对多
q2 = session.query(Favor.caption).filter(Favor.nid < 2)
ret = q1.union_all(q2).all()
import time
import threading
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy import create_engine
from sqlalchemy.sql import text
from sqlalchemy.engine.result import ResultProxy
from db import Users, Hosts
engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6", max_overflow=0, pool_size=5)
Session = sessionmaker(bind=engine)
session = Session()

查询

cursor = session.execute('select * from users')

result = cursor.fetchall()

添加

cursor = session.execute('insert into users(name) values(:value)',params={"value":'lqz'})
session.commit()
print(cursor.lastrowid)
session.close()
Copy
import time
import threading
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy import create_engine
from sqlalchemy.sql import text
from sqlalchemy.engine.result import ResultProxy
from db import Users, Hosts, Hobby, Person
engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8", max_overflow=0, pool_size=5
Session = sessionmaker(bind=engine)
session = Session()

添加

"""
session.add_all([
Hobby(caption='乒乓球'),
Hobby(caption='羽毛球'),
Person(name='张三', hobby_id=3),
Person(name='李四', hobby_id=4),
])
person = Person(name='张九', hobby=Hobby(caption='姑娘'))
session.add(person)

添加二

hb = Hobby(caption='人妖')
hb.pers = [Person(name='文飞'), Person(name='博雅')]
session.add(hb)
session.commit()
"""

使用relationship正向查询

"""
v = session.query(Person).first()
print(v.name)
print(v.hobby.caption)
"""

使用relationship反向查询

"""
v = session.query(Hobby).first()
print(v.caption)
print(v.pers)
"""

方式一，自己链表

person_list=session.query(models.Person.name,models.Hobby.caption).join(models.Hobby,isouter=True).all()

person_list=session.query(models.Person,models.Hobby).join(models.Hobby,isouter=True).all()
for row in person_list:

print(row.name,row.caption)

print(row[0].name,row[1].caption)

方式二：通过relationship

person_list=session.query(models.Person).all()
for row in person_list:
print(row.name,row.hobby.caption)

查询喜欢姑娘的所有人

obj=session.query(models.Hobby).filter(models.Hobby.id==1).first()
persons=obj.pers
print(persons)
session.close()
import time
import threading
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy import create_engine
from sqlalchemy.sql import text
from sqlalchemy.engine.result import ResultProxy
from db import Users, Hosts, Hobby, Person, Group, Server, Server2Group
engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8", max_overflow=0, pool_size=5
Session = sessionmaker(bind=engine)
session = Session()

添加

"""
session.add_all([
Server(hostname='c1.com'),
Server(hostname='c2.com'),
Group(name='A组'),
Group(name='B组'),
])
session.commit()
s2g = Server2Group(server_id=1, group_id=1)
session.add(s2g)
session.commit()
gp = Group(name='C组')

gp.servers = [Server(hostname='c3.com'),Server(hostname='c4.com')]
session.add(gp)
session.commit()
ser = Server(hostname='c6.com')
ser.groups = [Group(name='F组'),Group(name='G组')]
session.add(ser)
session.commit()
"""

使用relationship正向查询

"""
v = session.query(Group).first()
print(v.name)
print(v.servers)
"""

使用relationship反向查询

"""
v = session.query(Server).first()
print(v.hostname)
print(v.groups)
"""
session.close()
import time
import threading
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey, UniqueConstraint, Index
from sqlalchemy.orm import sessionmaker, relationship
from sqlalchemy import create_engine
from sqlalchemy.sql import text, func
from sqlalchemy.engine.result import ResultProxy
from db import Users, Hosts, Hobby, Person, Group, Server, Server2Group
engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/s6?charset=utf8", max_overflow=0, pool_size=5
Session = sessionmaker(bind=engine)
session = Session()

关联子查询:correlate(Group)表示跟Group表做关联，as_scalar相当于对该sql加括号，用于放在后面当子查询

subqry = session.query(func.count(Server.id).label("sid")).filter(Server.id == Group.id).correlate(Group).as_
result = session.query(Group.name, subqry)
"""
SELECT group.name AS group_name, (SELECT count(server.id) AS sid
FROM server
WHERE server.id = group.id) AS anon_1
FROM group
"""
'''
select * from tb where id in [select id from xxx];
select id,
name,

必须保证此次查询只有一个值

(select max(id) from xxx) as mid
from tb
例如，第三个字段只能有一个值
flask和SQLAchemy的管理者，通过他把他们做连接 离线脚本，创建表
详见代码
flask-migrate python3 manage.py db init 初始化：只执行一次
python3 manage.py db migrate 等同于 makemigartions
python3 manage.py db upgrade 等同于migrate