python 之sqlalchemy many to many

 1 # -*- coding: utf-8 -*-
 2 """
 3 @author: zengchunyun
 4 """
 5 from sqlalchemy import Column, Integer, String, Float, DateTime, ForeignKey, Table
 6 from sqlalchemy.orm import sessionmaker, relationship, backref
 7 from sqlalchemy.ext.declarative import declarative_base
 8 from sqlalchemy import create_engine
 9 
10 Base = declarative_base()
11 engine = create_engine('mysql+pymysql://root:123@127.0.0.1:3306/day11',echo=True)
12 
13 
14 
15 class Association(Base):
16     __tablename__ = 'association'
17     left_id = Column(Integer, ForeignKey("left.id"), primary_key=True)
18     right_id = Column(Integer, ForeignKey("right.id"), primary_key=True)
19     extra_data = Column(String(50))
20     child = relationship("Child", back_populates="parents")
21     parent = relationship("Parent", back_populates="children")
22 
23 
24 class Parent(Base):
25     __tablename__ = 'left'
26     id = Column(Integer, primary_key=True)
27     children = relationship("Association", back_populates='parent')
28 
29 class Child(Base):
30     __tablename__ = 'right'
31     id = Column(Integer, primary_key=True)
32     parents = relationship("Association", back_populates="child")
33 
34 
35 Base.metadata.create_all(engine)
36 
37 DBSession = sessionmaker()
38 DBSession.configure(bind=engine)
39 session = DBSession()  # 打开数据连接
40 
41 
42 # 插入数据方式一
43 # p = Parent()
44 # c = Child()
45 # a = Association(extra_data="ss")
46 # a.parent = p
47 # a.child = c
48 # 插入数据方式二
49 c = Child()
50 a = Association(extra_data='dd')
51 a.parent = Parent()
52 c.parents.append(a)
53 
54 # 插入数据方式三
55 # p = Parent()
56 # a = Association(extra_data="some data")
57 # a.child = Child()
58 # p.children.append(a)
59 #
60 # for assoc in p.children:
61 #     print(assoc.extra_data)
62 #     print(assoc.child)
63 
64 
65 session.add(a)
66 session.commit()

第二种方式

上面的其它代码不变，只修改relationship关系，效果是一样的

class Association(Base):
    __tablename__ = 'association'
    left_id = Column(Integer, ForeignKey("left.id"), primary_key=True)
    right_id = Column(Integer, ForeignKey("right.id"), primary_key=True)
    extra_data = Column(String(50))
    child = relationship("Child", backref="parents")
    parent = relationship("Parent", backref="children")


class Parent(Base):
    __tablename__ = 'left'
    id = Column(Integer, primary_key=True)

class Child(Base):
    __tablename__ = 'right'
    id = Column(Integer, primary_key=True)

 第三种方式，完整版

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
@author: zengchunyun
"""
from sqlalchemy import Column, Integer, String, Float, DateTime, ForeignKey, Table
from sqlalchemy.orm import sessionmaker, relationship, backref
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine

Base = declarative_base()
engine = create_engine('mysql+pymysql://root:123@127.0.0.1:3306/day11',echo=True)

class Association(Base):
    __tablename__ = 'association'
    left_id = Column(Integer, ForeignKey("left.id"), primary_key=True)
    right_id = Column(Integer, ForeignKey("right.id"), primary_key=True)
    extra_data = Column(String(50))
    child = relationship("Child")


class Parent(Base):
    __tablename__ = 'left'
    id = Column(Integer, primary_key=True)
    children = relationship("Association")

class Child(Base):
    __tablename__ = 'right'
    id = Column(Integer, primary_key=True)


Base.metadata.create_all(engine)

DBSession = sessionmaker()
DBSession.configure(bind=engine)
session = DBSession()  # 打开数据连接

p = Parent()
a = Association(extra_data='dasa')
a.child = Child()
p.children.append(a)
session.add(p)  #注意，这里必须先添加p，否则关系映射不成功
session.add(a)  #再添加a,记录就能添加成功了
session.commit()

以上三种方式最终效果是一样的，针对第三张表的写法还有另一种实现方式，通过Table创建，有时间再补上

many to many table形式

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
@author: zengchunyun
"""
from sqlalchemy import Column, Integer, String, Float, DateTime, ForeignKey, Table
from sqlalchemy.orm import sessionmaker, relationship, backref
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine

Base = declarative_base()
engine = create_engine('mysql+pymysql://root:123@127.0.0.1:3306/day11',echo=True)


PC = Table("p_c", Base.metadata,
           Column("left_id", Integer, ForeignKey("left.id")),
           Column("right_id",Integer, ForeignKey("right.id"))
           )

class Parent(Base):
    __tablename__ = 'left'
    id = Column(Integer, primary_key=True)
    name = Column(String(22))
    child = relationship("Child", secondary=PC)


class Child(Base):
    __tablename__ = 'right'
    id = Column(Integer, primary_key=True)
    name = Column(String(22))


Base.metadata.create_all(engine)

DBSession = sessionmaker()
DBSession.configure(bind=engine)
session = DBSession()  # 打开数据连接

p1 = Parent(name='zeng')
c1 = Child(name="haha")
p1.child.append(c1)  # 只有存在relationship关系的对象才能通过append形式添加记录
# 或者p1.child = [c1]
session.add(p1)
session.commit()

 Table形式二

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
@author: zengchunyun
"""
from sqlalchemy import Column, Integer, String, Float, DateTime, ForeignKey, Table
from sqlalchemy.orm import sessionmaker, relationship, backref
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine

Base = declarative_base()
engine = create_engine('mysql+pymysql://root:123@127.0.0.1:3306/day11',echo=True)


PC = Table("p_c", Base.metadata,
           Column("left_id", Integer, ForeignKey("left.id")),
           Column("right_id",Integer, ForeignKey("right.id"))
           )

class Parent(Base):
    __tablename__ = 'left'
    id = Column(Integer, primary_key=True)
    name = Column(String(22))
    child = relationship("Child", secondary=PC,
                         back_populates="parents")


class Child(Base):
    __tablename__ = 'right'
    id = Column(Integer, primary_key=True)
    name = Column(String(22))
    parents = relationship("Parent", secondary=PC,
                           back_populates="child")


Base.metadata.create_all(engine)

DBSession = sessionmaker()
DBSession.configure(bind=engine)
session = DBSession()  # 打开数据连接


# # 第一种数据插入方式
# p1 = Parent(name='zeng')
# c1 = Child(name="haha")
# p1.child.append(c1)  # 只有存在relationship关系的对象才能通过append形式添加记录
# # 或者p1.child = [c1]
# session.add(p1)
# 第二种
# p1 = Parent(name='zeng')
# c1 = Child(name='haha')
# c1.parents.append(p1)
# session.add(c1)
# 第三种
# p1 = Parent(name='zeng')
# p1.child = [Child(name="hah")]
# session.add(p1)
# 第四种
p1 = Parent(name="zcy", child=[Child(name='sasa')])
session.add(p1)
session.commit()

# 以上四种插入效果都是一样的

Table最后一种写法

PC = Table("p_c", Base.metadata,
           Column("left_id", Integer, ForeignKey("left.id")),
           Column("right_id",Integer, ForeignKey("right.id"))
           )

class Parent(Base):
    __tablename__ = 'left'
    id = Column(Integer, primary_key=True)
    name = Column(String(22))
    child = relationship("Child", secondary=PC,
                         backref="parents")


class Child(Base):
    __tablename__ = 'right'
    id = Column(Integer, primary_key=True)
    name = Column(String(22))

以上几种Table形式多对多写法效果是一样的，只是在查询上有一定区别，

第二种table与第三种其实是完全一样的效果