Python开发【十二章】：ORM sqlalchemy

一、对象映射关系（ORM）

orm英文全称object relational mapping,就是对象映射关系程序，简单来说我们类似python这种面向对象的程序来说一切皆对象，但是我们使用的数据库却都是关系型的，为了保证一致的使用习惯，通过orm将编程语言的对象模型和数据库的关系模型建立映射关系，这样我们在使用编程语言对数据库进行操作的时候可以直接使用编程语言的对象模型进行操作就可以了，而不用直接使用sql语言

优点：

• 隐藏了数据访问细节，“封闭”的通用数据库交互，ORM的核心。他使得我们的通用数据库交互变得简单易行，并且完全不用考虑该死的SQL语句。快速开发，由此而来
• ORM使我们构造固化数据结构变得简单易行

缺点：

• 无可避免的，自动化意味着映射和关联管理，代价是牺牲性能（早期，这是所有不喜欢ORM人的共同点）。现在的各种ORM框架都在尝试使用各种方法来减轻这块（LazyLoad，Cache），效果还是很显著的

二、SQLAlchemy

在Python中，最有名的ORM框架是SQLAlchemy。用户包括openstack＼Dropbox等知名公司或应用

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 MySQLdb模块
    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...]

更多详见：http://docs.sqlalchemy.org/en/latest/dialects/index.html

注：支持连接MySQL、Oracles数据库

安装：

pip install SQLAlchemy
pip install pymysql
#由于mysqldb依然不支持py3，所以这里我们用pymysql与sqlalchemy交互

windows下python2.7环境MySQLdb模块安装

官网http://www.codegood.com/downloads下载  MySQL-python-1.2.3.win32-py2.7.exe文件
下载完成后本地安装
执行命令pip install MySQL-python完成，本地import MySQLdb

1、基本使用

查看mysql基础知识移步-》》http://www.cnblogs.com/lianzhilei/p/5993282.html

下面就开始让你见证orm的nb之处，盘古开天劈地之前，我们创建一个表是这样的：

CREATE TABLE user (
    id INTEGER NOT NULL AUTO_INCREMENT,
    name VARCHAR(32),
    password VARCHAR(64),
    PRIMARY KEY (id)
)

这只是最简单的sql表，如果再加上外键关联什么的，一般程序员的脑容量是记不住那些sql语句的，于是有了orm,实现上面同样的功能，代码如下：

# 创建表结构

import sqlalchemy
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import  declarative_base
from sqlalchemy import Column,Integer,String

engine = create_engine("mysql+pymysql://root:zyw@123@192.168.20.219/lzl",
                       encoding="utf-8",echo=True)      #echo=True 打印程序运行详细信息

Base = declarative_base()   #生成orm基类

class User(Base):
    __tablename__ = "user"      #表名
    id = Column(Integer,primary_key=True)
    name = Column(String(32))
    password = Column(String(64))

Base.metadata.create_all(engine)    #创建表结构

# 打印输出
# 2016-10-26 08:42:02,619 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'sql_mode'
# 2016-10-26 08:42:02,619 INFO sqlalchemy.engine.base.Engine {}
# 2016-10-26 08:42:02,622 INFO sqlalchemy.engine.base.Engine SELECT DATABASE()
# 2016-10-26 08:42:02,622 INFO sqlalchemy.engine.base.Engine {}
# 2016-10-26 08:42:02,624 INFO sqlalchemy.engine.base.Engine show collation where `Charset` = 'utf8' and `Collation` = 'utf8_bin'
# 2016-10-26 08:42:02,624 INFO sqlalchemy.engine.base.Engine {}
# 2016-10-26 08:42:02,649 INFO sqlalchemy.engine.base.Engine SELECT CAST('test plain returns' AS CHAR(60)) AS anon_1
# 2016-10-26 08:42:02,649 INFO sqlalchemy.engine.base.Engine {}
# 2016-10-26 08:42:02,651 INFO sqlalchemy.engine.base.Engine SELECT CAST('test unicode returns' AS CHAR(60)) AS anon_1
# 2016-10-26 08:42:02,651 INFO sqlalchemy.engine.base.Engine {}
# 2016-10-26 08:42:02,652 INFO sqlalchemy.engine.base.Engine SELECT CAST('test collated returns' AS CHAR CHARACTER SET utf8)
# COLLATE utf8_bin AS anon_1
# 2016-10-26 08:42:02,652 INFO sqlalchemy.engine.base.Engine {}
# 2016-10-26 08:42:02,655 INFO sqlalchemy.engine.base.Engine DESCRIBE `user`
# 2016-10-26 08:42:02,655 INFO sqlalchemy.engine.base.Engine {}
# 2016-10-26 08:42:02,657 INFO sqlalchemy.engine.base.Engine ROLLBACK
# 2016-10-26 08:42:02,660 INFO sqlalchemy.engine.base.Engine
# CREATE TABLE user (
# 	id INTEGER NOT NULL AUTO_INCREMENT,
# 	name VARCHAR(32),
# 	password VARCHAR(64),
# 	PRIMARY KEY (id)
# )
#
#
# 2016-10-26 08:42:02,660 INFO sqlalchemy.engine.base.Engine {}
# 2016-10-26 08:42:02,904 INFO sqlalchemy.engine.base.Engine COMMIT

查询表结构：

mysql> desc user;
+----------+-------------+------+-----+---------+----------------+
| Field    | Type        | Null | Key | Default | Extra          |
+----------+-------------+------+-----+---------+----------------+
| id       | int(11)     | NO   | PRI | NULL    | auto_increment |
| name     | varchar(32) | YES  |     | NULL    |                |
| password | varchar(64) | YES  |     | NULL    |                |
+----------+-------------+------+-----+---------+----------------+
3 rows in set (0.01 sec) 

你说，娘那个腚的，并没有感觉代码量变少啊，呵呵， 孩子莫猴急，好戏在后面

除上面的创建之外，还有一种创建表的方式，虽不常用，但还是看看吧

from sqlalchemy import Table, MetaData, Column, Integer, String, ForeignKey
from sqlalchemy.orm import mapper

metadata = MetaData()

user = Table('user', metadata,
            Column('id', Integer, primary_key=True),
            Column('name', String(50)),
            Column('fullname', String(50)),
            Column('password', String(12))
        )

class User(object):
    def __init__(self, name, fullname, password):
        self.name = name
        self.fullname = fullname
        self.password = password

mapper(User, user) #the table metadata is created separately with the Table construct, then associated with the User class via the mapper() function

另一种方式

2、创建数据

最基本的表我们创建好了，那我们开始用orm创建一条数据试试

# 创建表数据

from sqlalchemy import  create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import String,Integer,Column
from sqlalchemy.orm import sessionmaker

engine = create_engine("mysql+pymysql://root:zyw@123@192.168.20.219/lzl",
                       encoding="utf-8")

Base = declarative_base()   #生成orm基类

class User(Base):
    __tablename__ = "user"      #表名
    id = Column(Integer,primary_key=True)
    name = Column(String(32))
    password = Column(String(64))

#Base.metadata.create_all(engine)    #创建表结构

Session_class = sessionmaker(bind=engine)   #Session_class现在不是实例，而是类
Session = Session_class()   #生成Session实例

user_obj = User(name="lzl",password="123456")   #生成你要创建的数据对象
print(user_obj.name,user_obj.id)  #此时还没创建对象呢，不信你打印一下id发现还是None

Session.add(user_obj) #把要创建的数据对象添加到这个session里， 一会统一创建
print(user_obj.name,user_obj.id) #此时也依然还没创建

Session.commit()    #现此才统一提交，创建数据

# lzl None
# lzl None

我擦，写这么多代码才创建一条数据，你表示太tm的费劲了，正要转身离开，我拉住你的手不放开，高潮快来了。。

3、查询数据

# 查询

from sqlalchemy import  create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import String,Integer,Column
from sqlalchemy.orm import sessionmaker

engine = create_engine("mysql+pymysql://root:zyw@123@192.168.20.219/lzl",
                       encoding="utf-8")

Base = declarative_base()   #生成orm基类

class User(Base):
    __tablename__ = "user"      #表名
    id = Column(Integer,primary_key=True)
    name = Column(String(32))
    password = Column(String(64))

Session_class = sessionmaker(bind=engine)   #Session_class现在不是实例，而是类
Session = Session_class()   #生成Session实例

my_user = Session.query(User).filter_by(name="lzl").first()
print(my_user)          #my_user此时是一个对象
#<__main__.User object at 0x03EFC6D0>

print(my_user.id,my_user.name,my_user.password)
# 1 lzl 123456

不过刚才上面的显示的内存对象对址你是没办法分清返回的是什么数据的，除非打印具体字段看一下，如果想让它变的可读，只需在定义表的类下面加上这样的代码：

def __repr__(self):
　　return "<User(name='%s',  password='%s')>" % (
　　self.name, self.password)

print(my_user)
#<User(name='lzl',  password='123456')>

获取所有数据：

#当前数据表信息

mysql> select * from user;
+----+------------+----------+
| id | name       | password |
+----+------------+----------+
|  1 | lianzhilei | 123456   |
|  2 | lzl        | 123456   |
|  3 | lzl        | 123456   |
|  6 | alex       | 34567    |
|  7 | alex       | 34567    |
|  8 | wupeiqi    | 33422    |
+----+------------+----------+
6 rows in set (0.00 sec)

print(Session.query(User.name,User.id).all() )
# [('lianzhilei', 1), ('lzl', 2), ('lzl', 3), ('alex', 6), ('alex', 7), ('wupeiqi', 8)]

多条件查询：

# 多条件查询

from sqlalchemy import  create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import String,Integer,Column
from sqlalchemy.orm import sessionmaker
from sqlalchemy import func

engine = create_engine("mysql+pymysql://root:zyw@123@192.168.20.219/lzl",
                       encoding="utf-8")

Base = declarative_base()   #生成orm基类

class User(Base):
    __tablename__ = "user"      #表名
    id = Column(Integer,primary_key=True)
    name = Column(String(32))
    password = Column(String(64))

    def __repr__(self):
        return "<User(name='%s',  password='%s')>" % (
        self.name, self.password)

Session_class = sessionmaker(bind=engine)   #Session_class现在不是实例，而是类
Session = Session_class()   #生成Session实例

objs = Session.query(User).filter(User.id>3).filter(User.id<8).all()
print(objs)
# [<User(name='alex',  password='34567')>, <User(name='alex',  password='34567')>]

统计：

# 统计

from sqlalchemy import  create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import String,Integer,Column
from sqlalchemy.orm import sessionmaker
from sqlalchemy import func

engine = create_engine("mysql+pymysql://root:zyw@123@192.168.20.219/lzl",
                       encoding="utf-8")

Base = declarative_base()   #生成orm基类

class User(Base):
    __tablename__ = "user"      #表名
    id = Column(Integer,primary_key=True)
    name = Column(String(32))
    password = Column(String(64))

    def __repr__(self):
        return "<User(name='%s',  password='%s')>" % (
        self.name, self.password)

Session_class = sessionmaker(bind=engine)   #Session_class现在不是实例，而是类
Session = Session_class()   #生成Session实例

print(Session.query(User).filter(User.name.like("l%")).count())
#3

分组：

# 分组

from sqlalchemy import  create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import String,Integer,Column
from sqlalchemy.orm import sessionmaker
from sqlalchemy import func

engine = create_engine("mysql+pymysql://root:zyw@123@192.168.20.219/lzl",
                       encoding="utf-8")

Base = declarative_base()   #生成orm基类

class User(Base):
    __tablename__ = "user"      #表名
    id = Column(Integer,primary_key=True)
    name = Column(String(32))
    password = Column(String(64))

    def __repr__(self):
        return "<User(name='%s',  password='%s')>" % (
        self.name, self.password)

Session_class = sessionmaker(bind=engine)   #Session_class现在不是实例，而是类
Session = Session_class()   #生成Session实例

print(Session.query(func.count(User.name),User.name).group_by(User.name).all())
#[(2, 'alex'), (1, 'lianzhilei'), (2, 'lzl'), (1, 'wupeiqi')]

相当于原生sql为

SELECT count(user.name) AS count_1, user.name AS user_name
FROM user GROUP BY user.name

4、修改

# 修改

from sqlalchemy import  create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import String,Integer,Column
from sqlalchemy.orm import sessionmaker

engine = create_engine("mysql+pymysql://root:zyw@123@192.168.20.219/lzl",
                       encoding="utf-8")

Base = declarative_base()   #生成orm基类

class User(Base):
    __tablename__ = "user"      #表名
    id = Column(Integer,primary_key=True)
    name = Column(String(32))
    password = Column(String(64))

    def __str__(self):
        return "<User(name='%s',  password='%s')>" % (
        self.name, self.password)

Session_class = sessionmaker(bind=engine)   #Session_class现在不是实例，而是类
Session = Session_class()   #生成Session实例

my_user = Session.query(User).filter_by(name="lzl").first()
print(my_user)
#<User(name='lzl',  password='123456')>

my_user.name = "lianzhilei"

Session.commit()    #提交数据

mysql> select * from user;
+----+------------+----------+
| id | name       | password |
+----+------------+----------+
|  1 | lianzhilei | 123456   |
|  2 | lzl        | 123456   |
|  3 | lzl        | 123456   |
+----+------------+----------+
3 rows in set (0.00 sec)

5、回滚

# 回滚

from sqlalchemy import  create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import String,Integer,Column
from sqlalchemy.orm import sessionmaker

engine = create_engine("mysql+pymysql://root:zyw@123@192.168.20.219/lzl",
                       encoding="utf-8")

Base = declarative_base()   #生成orm基类

class User(Base):
    __tablename__ = "user"      #表名
    id = Column(Integer,primary_key=True)
    name = Column(String(32))
    password = Column(String(64))

    def __repr__(self):
        return "<User(name='%s',  password='%s')>" % (
        self.name, self.password)

Session_class = sessionmaker(bind=engine)   #Session_class现在不是实例，而是类
Session = Session_class()   #生成Session实例

my_user = Session.query(User).filter_by(id = 1).first()
my_user.name = "Jack"
print(my_user)
# <User(name='Jack',  password='123456')>

Rain_user = User(name="Rain",password="12345")
Session.add(Rain_user)
print(Session.query(User).filter(User.name.in_(["Jack","Rain"])).all()) # 这时看session里有你刚添加和修改的数据
#[<User(name='Jack',  password='123456')>, <User(name='Rain',  password='12345')>]

Session.rollback()

print(Session.query(User).filter(User.name.in_(["Jack","Rain"])).all())  #再查就发现刚才添加的数据没有了。
#[]

 6、外键关联

我们先创建个study_record表与student进行关联

# 外键关联

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import String,Column,Integer,ForeignKey,DATE
from sqlalchemy.orm import sessionmaker,relationship

engine = create_engine("mysql+pymysql://root:zyw@123@192.168.0.59/lzl",
                       encoding="utf-8")

Base = declarative_base()

class Student(Base):
    __tablename__ ="student"
    id = Column(Integer,primary_key=True)
    name = Column(String(32),nullable=False)
    register_date = Column(DATE,nullable=False)

    def __repr__(self):
        return "<%s name:%s>"%(self.id,self.name)

class StudyRecord(Base):
    __tablename__ = "study_record"
    id = Column(Integer,primary_key=True)
    day = Column(Integer,nullable=False)
    status = Column(String(32),nullable=False)
    stu_id = Column(Integer,ForeignKey("student.id")) #关联student表里的id

    my_student = relationship("Student",backref="my_study_record") # Student为关联的类 

    def __repr__(self):
        return "<%s name:%s>" % (self.id, self.name)

Base.metadata.create_all(engine)

Session_class = sessionmaker(bind=engine)
session = Session_class()

s1 = Student(name="lzl",register_date="2016-10-26")
s2 = Student(name="alex",register_date="2015-10-26")
s3 = Student(name="eric",register_date="2014-10-26")
s4 = Student(name="rain",register_date="2013-10-26")

r1 = StudyRecord(day=1,status="YES",stu_id=1)
r2 = StudyRecord(day=2,status="No",stu_id=1)
r3 = StudyRecord(day=3,status="YES",stu_id=1)
r4 = StudyRecord(day=1,status="YES",stu_id=2)

session.add_all([s1,s2,s3,s4,r1,r2,r3,r4])
session.commit()

注：my_student = relationship("Student",backref="my_study_record")这个nb，允许你在user表里通过backref字段反向查出所有它在addresses表里的关联项

查询：

# 外键查询

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import String,Column,Integer,ForeignKey,DATE
from sqlalchemy.orm import sessionmaker,relationship

engine = create_engine("mysql+pymysql://root:zyw@123@192.168.0.59/lzl",
                       encoding="utf-8")

Base = declarative_base()

class Student(Base):
    __tablename__ ="student"
    id = Column(Integer,primary_key=True)
    name = Column(String(32),nullable=False)
    register_date = Column(DATE,nullable=False)

    def __repr__(self):
        return "<id:%s name:%s>"%(self.id,self.name)

class StudyRecord(Base):
    __tablename__ = "study_record"
    id = Column(Integer,primary_key=True)
    day = Column(Integer,nullable=False)
    status = Column(String(32),nullable=False)
    stu_id = Column(Integer,ForeignKey("student.id")) #关联student表里的id

    my_student = relationship("Student",backref="my_study_record") # Student为关联的类

    def __repr__(self):
        return "<name:%s day:%s status:%s>" % (self.my_student.name,self.day,self.status)

Base.metadata.create_all(engine)

Session_class = sessionmaker(bind=engine)
session = Session_class()

stu_obj = session.query(Student).filter(Student.name=="lzl").first()
print(stu_obj)
#<id:1 name:lzl>

print(stu_obj.my_study_record)
#[<name:lzl day:1 status:YES>, <name:lzl day:2 status:No>, <name:lzl day:3 status:YES>]

　　

 7、多外键关联

下表中，Customer表有2个字段都关联了Address表，首先先创建表结构

# 多外键关联

from sqlalchemy import create_engine
from sqlalchemy import Integer,String,Column,ForeignKey
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker,relationship

engine = create_engine("mysql+pymysql://root:zyw@123@192.168.20.219/lzl",
                       encoding="utf-8",echo= True)

Base =  declarative_base()

class Customer(Base):
    __tablename__ = "customer"
    id = Column(Integer,primary_key=True)
    name = Column(String(32))
    billing_address_id = Column(Integer,ForeignKey("address.id"))
    shipping_address_id = Column(Integer, ForeignKey("address.id"))

    billing_address = relationship("Address",foreign_keys=[billing_address_id]) #必须写foreign_keys
    shipping_address = relationship("Address",foreign_keys=[shipping_address_id])

class Address(Base):
    __tablename__ = 'address'
    id = Column(Integer, primary_key=True)
    street = Column(String(32))
    city = Column(String(32))
    state = Column(String(32))

Base.metadata.create_all(engine)

mysql> desc address;
+--------+-------------+------+-----+---------+----------------+
| Field  | Type        | Null | Key | Default | Extra          |
+--------+-------------+------+-----+---------+----------------+
| id     | int(11)     | NO   | PRI | NULL    | auto_increment |
| street | varchar(32) | YES  |     | NULL    |                |
| city   | varchar(32) | YES  |     | NULL    |                |
| state  | varchar(32) | YES  |     | NULL    |                |
+--------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

mysql> desc customer;
+---------------------+-------------+------+-----+---------+----------------+
| Field               | Type        | Null | Key | Default | Extra          |
+---------------------+-------------+------+-----+---------+----------------+
| id                  | int(11)     | NO   | PRI | NULL    | auto_increment |
| name                | varchar(32) | YES  |     | NULL    |                |
| billing_address_id  | int(11)     | YES  | MUL | NULL    |                |
| shipping_address_id | int(11)     | YES  | MUL | NULL    |                |
+---------------------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

生成数据：

Session = sessionmaker(bind=engine)
session = Session()

a1 = Address(street="Tiantongyuan",city="ChangPing",state="BJ")
a2 = Address(street="Wudaokou",city="HaiDian",state="BJ")
a3 = Address(street="Yanjiao",city="LangFang",state="HB")

session.add_all([a1,a2,a3])
c1 = Customer(name="lzl",billing_address_id=1,shipping_address_id=2)
c2 = Customer(name="Alex",billing_address_id=3,shipping_address_id=3)

session.add_all([c1,c2])

session.commit()

查询数据：

class Customer(Base):
    __tablename__ = "customer"
    id = Column(Integer,primary_key=True)
    name = Column(String(32))
    billing_address_id = Column(Integer,ForeignKey("address.id"))
    shipping_address_id = Column(Integer, ForeignKey("address.id"))

    billing_address = relationship("Address",foreign_keys=[billing_address_id]) #必须写foreign_keys
    shipping_address = relationship("Address",foreign_keys=[shipping_address_id])

    def __repr__(self):
        return "<name:%s billing_add:%s shipping_add:%s>"%(self.name,self.billing_address.street,
                                                           self.shipping_address.street)

#Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine)
session = Session()

cus_obj = session.query(Customer).filter_by(name="lzl").first()
print(cus_obj)
# <name:lzl billing_add:Tiantongyuan shipping_add:Wudaokou>

　　

 8、多对多关联

现在来设计一个能描述“图书”与“作者”的关系的表结构，需求是

1. 一本书可以有好几个作者一起出版
2. 一个作者可以写好几本书

创建表结构：

#一本书可以有多个作者，一个作者又可以出版多本书

from sqlalchemy import Table, Column, Integer,String,DATE, ForeignKey
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

engine = create_engine("mysql+pymysql://root:zyw@123@192.168.20.219/lzl",
                       encoding="utf-8")

Base = declarative_base()

#创建book_m2m_author表，表不用用户操作，系统自动维护，自动添加数据
book_m2m_author = Table('book_m2m_author', Base.metadata,
                        Column('book_id',Integer,ForeignKey('books.id')),
                        Column('author_id',Integer,ForeignKey('authors.id')),
                        )

class Book(Base):
    __tablename__ = 'books'
    id = Column(Integer,primary_key=True)
    name = Column(String(64))
    pub_date = Column(DATE)
    #关联Author类，secondary表示通过book_m2m_author表进行查询关联数据，backref反向查询也一样
    authors = relationship('Author',secondary=book_m2m_author,backref='books')

    def __repr__(self):
        return self.name

class Author(Base):
    __tablename__ = 'authors'
    id = Column(Integer, primary_key=True)
    name = Column(String(32))

    def __repr__(self):
        return self.name

Base.metadata.create_all(engine)

创建表数据：　

#创建数据

Session = sessionmaker(bind=engine)
session = Session()

b1 = Book(name="learn python with Alex",pub_date="2014-05-02")
b2 = Book(name="learn linux with Alex",pub_date="2015-05-02")
b3 = Book(name="learn go with Alex",pub_date="2016-05-02")

a1 = Author(name="Alex")
a2 = Author(name="Jack")
a3 = Author(name="Rain")

#关键来了，创建关联关系
b1.authors = [a1,a3]
b3.authors = [a1,a2,a3]

session.add_all([b1,b2,b3,a1,a2,a3])
session.commit()

mysql> select * from book_m2m_author;
+---------+-----------+
| book_id | author_id |
+---------+-----------+
|       1 |         1 |
|       2 |         1 |
|       2 |         2 |
|       1 |         3 |
|       2 |         3 |
+---------+-----------+
5 rows in set (0.00 sec)

mysql> select * from authors;
+----+------+
| id | name |
+----+------+
|  1 | Alex |
|  2 | Jack |
|  3 | Rain |
+----+------+
3 rows in set (0.00 sec)

mysql> select * from books;
+----+------------------------+------------+
| id | name                   | pub_date   |
+----+------------------------+------------+
|  1 | learn python with Alex | 2014-05-02 |
|  2 | learn go with Alex     | 2016-05-02 |
|  3 | learn linux with Alex  | 2015-05-02 |
+----+------------------------+------------+
3 rows in set (0.00 sec)

查询：

author_obj = session.query(Author).filter_by(name="Alex").first()
print(author_obj,author_obj.books)

book_obj = session.query(Book).filter_by(id=2).first()
print(book_obj,book_obj.authors)

# Alex [learn python with Alex, learn go with Alex]
# learn go with Alex [Alex, Jack, Rain]

　　

9、多对多删除

删除数据时不用管boo_m2m_authors　， sqlalchemy会自动帮你把对应的数据删除

通过书删除作者

author_obj =s.query(Author).filter_by(name="Jack").first()

book_obj = s.query(Book).filter_by(name="跟Alex学把妹").first()

book_obj.authors.remove(author_obj) #从一本书里删除一个作者
s.commit()

直接删除作者　

删除作者时，会把这个作者跟所有书的关联关系数据也自动删除

author_obj =s.query(Author).filter_by(name="Alex").first()
# print(author_obj.name , author_obj.books)
s.delete(author_obj)
s.commit()

10、中文

engine = create_engine("mysql+pymysql://root:zyw@123@192.168.20.219/lzl?charset=utf8")

#修改查看数据库字符编码
mysql> alter database lzl character set utf8;
Query OK, 1 row affected (0.00 sec)

mysql>  show variables like 'character_set_database';
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| character_set_database | utf8  |