SQLAlchemy,flask-sqlalchemy

        <div class="clear"></div>
        <div class="postBody">

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。

pip3 install sqlalchemy

组成部分：

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

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：

MySQL-Python
    mysql+mysqldb://<user>:<password>@<host>[:<port>]/<dbname>
pymysql

mysql+pymysql://<username>:<password>@<host>/<dbname>[?<options>]
MySQL-Connector

mysql+mysqlconnector://<user>:<password>@<host>[:<port>]/<dbname>
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

django中如何反向生成models

python manage.py inspectdb > app/models.py

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）

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()

2 orm使用

models.py

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)

if name == 'main':

# drop_db()

init_db()

app.py

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()

3.一对多关系

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')</code></pre>

4.多对多关系
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)

# 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')


5.操作数据表
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()


6.基于scoped_session实现线程安全
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()


7.基本增删查改
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(Users.id).all()
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()


8.常用操作
#　条件
ret = session.query(Users).filter_by(name='lqz').all()
#表达式，and条件连接
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)

q2 = session.query(Favor.caption).filter(Favor.nid < 2)

ret = q1.union_all(q2).all()


9.执行原生sql
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()


10.一对多
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()


11.多对多
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()


12.其它
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_scalar()

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

id name  mid

1  lqz   1，2  不合理

2  egon   2
'''

'''

成绩表：

id sid    cid    score

1  1      物理      99

2  1      化学      88

3  2      物理      95
学生表：

id   name  每个学生总分数

1     xx      88

2     yy       77
select id，name,

(select avr(score) from 成绩表 where 成绩表.sid=学生表.id) as x

from 学生表

subqry = session.query(func.count(成绩表.scort).label("sc")).filter(学生表.id == 成绩表.sid).correlate(学生表).as_scalar()

result = session.query(学生表.name, subqry)
'''
原生SQL
"""
查询
cursor = session.execute('select * from users')

result = cursor.fetchall()
添加
cursor = session.execute('insert into users(name) values(:value)',params={"value":'wupeiqi'})

session.commit()

print(cursor.lastrowid)

"""
session.close()


13.Flask-SQLAlchemy
flask和SQLAchemy的管理者，通过他把他们做连接
db = SQLAlchemy()
    - 包含配置
    - 包含ORM基类
    - 包含create_all
    - engine
    - 创建连接

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

查看全文