Python 9 sqlalchemy ORM

Posted 2020-10-15 灬魑魅魍魉灬

一、ORM介绍：

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。

orm的优点：

1. 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。
2. ORM使我们构造固化数据结构变得简单易行。

缺点：

1. 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安装

pip install SQLAlchemy
pip install pymysql

连接数据库：
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...]

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

 三、sqlalchemy基本使用

创建表：

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://cheng:[email protected]/test_cheng‘,
                       encoding = ‘utf-8‘,echo=True)

Base = declarative_base()  #生成基类

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

插入数据：

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

engine = create_engine(‘mysql+pymysql://cheng:[email protected]/test_cheng‘,
                       encoding = ‘utf-8‘,echo=True)

Base = declarative_base()

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

Session_class = sessionmaker(bind=engine)
Session = Session_class()
for i in range(10):
    user_obj = User(name=‘cheng%s‘%i,password=‘%s*321‘%i)
    Session.add(user_obj)
    
Session.commit()

查询和修改数据：

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

engine = create_engine(‘mysql+pymysql://cheng:[email protected]/test_cheng‘,
                       encoding = ‘utf-8‘)

Base = declarative_base()

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

Session_class = sessionmaker(bind=engine)
Session = Session_class()
#1.first生成一个实例，而all生成一个实例列表：
my_user = Session.query(User).filter_by(name=‘cheng77‘).first()
print(my_user.id,my_user.name,my_user.password)

my_user = Session.query(User).filter_by(name = ‘cheng78‘).all()
for i in my_user:
    print(i.id,i.name,i.password)

#2.filter_by不支持<,>,==,而filter支持<,>,==而且filter支持多条件查询：
my_user = Session.query(User).filter(User.id < 29).filter(User.id > 13).all()
for i in my_user:
    print(i.id,i.name,i.password)

#3.修改数据：
my_user = Session.query(User).filter_by(name=‘cheng77‘).first()
my_user.name = ‘cheng77777‘
Session.commit()
print(my_user.id,my_user.name,my_user.password)

#4.回滚：
<----插入数据---->
Session.rollback()
<----查询数据没有插入---->

#5.统计和分组：
conn = Session.query(User).filter(User.name.like(‘ch%‘)).count()
print(conn)

from sqlalchemy import func
list_group = Session.query(func.count(User.name),User.name).group_by(User.name).all()
for i in list_group:
    print(i)

#6.将查询的数据可读：
  def __repr__(self):
      return "<User(name=‘%s‘, password=‘%s‘)>" % (self.name, self.password)    #在User类里添加
 my_user = Session.query(User.name,User.password).all()
 print(my_user)

 外键关联：

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column,String,Integer,ForeignKey,DATE
from sqlalchemy.orm import sessionmaker,relationship
from sqlalchemy import func
engine = create_engine(‘mysql+pymysql://cheng:[email protected]/test_cheng‘,
                       encoding = ‘utf-8‘)


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

    def __repr__(self):
        return ‘id:%s,name:%s‘%(self.id,self.name)

class Study_record(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‘))    #创建外键关联

    student = relationship(‘Student‘,backref=‘my_study_record‘)  #允许你在student表里通过backref字段反向查出study_record表里的字段。
    def __repr__(self):
        #return ‘id:%s,day:%s,stu_id:%s‘%(self.id,self.day,self.stu_id)
        return ‘id:%s,day:%s,stu_id:%s‘ % (self.id, self.day, self.student.name)    #通过self.student.name调出student表里name字段的值。
Base.metadata.create_all(engine)

Session_class = sessionmaker(bind=engine)
Session = Session_class()
data = Session.query(Student).filter(Student.name==‘cheng‘).first()   #查出name等于cheng的学生，再打印出Study_record类里repr的返回值。
print(data.my_study_record)


# stu_obj = Student(name=‘cheng1‘,data = ‘2017-11-01‘)
# record_obj = Study_record(day=2,status =‘yes‘,stu_id=3)  #插入数据时先创建student表里的主键，在创建study_record的外键，因为有外键约束
# Session.add_all([record_obj])
# Session.commit()

 多外键关联：

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column,String,Integer,ForeignKey,DATE
from sqlalchemy.orm import sessionmaker,relationship
engine = create_engine(‘mysql+pymysql://cheng:[email protected]/test_cheng?charset=utf8‘,
                       encoding=‘utf-8‘)

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])
    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)

Session_class = sessionmaker(bind=engine)
Session = Session_class()
#address_obj = Address(street =‘tongzhou1‘,city =‘beijing2‘,state=‘beijing3‘)
address_obj = Address(street =‘通州‘,city =‘北京‘,state=‘北京‘)
Session.add_all([address_obj])
customer_obj = Customer(name=‘chengll‘,billing_address=address_obj,shipping_address=address_obj)   #通过以上关联，可以这样进行赋值
Session.add_all([customer_obj])
Session.commit()

 多对多：

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:[email protected]/cuichao?charset=utf8‘,encoding=‘utf-8‘)
Base = declarative_base()

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)
    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)

Session_class = sessionmaker(bind=engine)  # 创建与数据库的会话session class ,注意,这里返回给session的是个class,不是实例
s = Session_class()  # 生成session实例

b1 = Book(name="跟Alex学Python")
b2 = Book(name="跟Alex学把妹")
b3 = Book(name="跟Alex学装逼")
b4 = Book(name="跟Alex学开车")

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

b1.authors = [a1, a2]
b2.authors = [a1, a2, a3]

s.add_all([b1, b2, b3, b4, a1, a2, a3])

s.commit()
# print(‘--------通过书表查关联的作者---------‘)
#
# book_obj = s.query(Book).filter_by(name="跟Alex学Python").first()
# print(book_obj.name, book_obj.authors)
#
# print(‘--------通过作者表查关联的书---------‘)
# author_obj = s.query(Author).filter_by(name="Alex").first()
# print(author_obj.name, author_obj.books)
# s.commit()