Python ORM框架之SQLALchemy

Posted 2020-11-25 Feng_Forest

ORM框架本质: 让面向对象的类跟数据库中的表做个对应关系

ORM与原生SQL比较：

1. 原生SQL性能较好
2. 原生SQL的可维护性相对差一些
3. ORM操作、开发起来比较简单、快捷

Python ORM框架：SQLALchemy、Django、Storm、SQLObject

SQLALchemy与Django比较：

• Django操作起来更简单，双下划线跨表查询更方便
• Django支持自动生成第三张表
• SQLALchemy更接近原生SQL
• 两者都是通过DB API（pymysql 、mysqlDB）模块连接数据库
• 默认SQLALchemy不能修改表的字段，只能创建表、删除表

SQLALchemy框架：

 

•  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类型
• Schema / Type ： 架构和类型
• SQL Expression Language： SQL表达式语言

SQLALchemy本身无法操作数据库，需要依赖pymysql第三方模块，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

使用pymysql连接数据库格式：

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

 

 1 import datetime
 2 from sqlalchemy import create_engine
 3 from sqlalchemy.ext.declarative import declarative_base
 4 from sqlalchemy import Column, Integer, String, Text, ForeignKey, DateTime, UniqueConstraint, Index
 5 from sqlalchemy.orm import relationship, sessionmaker
 6 from sqlalchemy.sql import text
 7 
 8 Base = declarative_base()
 9 
10 
11 class Users(Base):
12     """
13     单表创建
14     """
15     __tablename__ = \'users\'
16     id = Column(Integer, primary_key=True, autoincrement=True)
17     name = Column(String(32), index=True, nullable=False)
18     email = Column(String(32), unique=True)
19     ctime = Column(DateTime, default=datetime.datetime.now)
20     extra = Column(Text, nullable=True)
21 
22     __table_args__ = (
23         UniqueConstraint(\'id\', \'name\', name=\'uix_id_name\'),
24         Index(\'ix_id_name\', \'name\', \'email\'),
25     )
26 
27 
28 # 一对多示例
29 class Hobby(Base):
30     __tablename__ = \'hobby\'
31     id = Column(Integer, primary_key=True)
32     caption = Column(String(50), nullable=True)
33 
34 
35 class Person(Base):
36     __tablename__ = \'person\'
37     id = Column(Integer, primary_key=True, autoincrement=True)
38     name = Column(String(32), nullable=False)
39     hobby_id = Column(Integer, ForeignKey("hobby.id"))  # hobby.id 中的hobby指的是tablename
40 
41     # 与生成表结构无关， 仅用于查询方便
42     hobby = relationship(\'Hobby\', backref=\'pers\')  # 此处Hobby指的是类名
43 
44 
45 # 多对多示例
46 class Server(Base):
47     __tablename__ = \'server\'
48     id = Column(Integer, primary_key=True, autoincrement=True)
49     hostname = Column(String(64), unique=True, nullable=False)
50 
51 
52 class Group(Base):
53     __tablename__ = \'group\'
54     id = Column(Integer, primary_key=True)
55     name = Column(String(64), unique=True, nullable=False)
56 
57     # 与生成表无关，仅用于查询方便
58     servers = relationship(\'Server\', secondary=\'server2group\', backref=\'groups\')
59 
60 
61 class Server2Grouop(Base):
62     __tablename__ = \'server2group\'
63     id = Column(Integer, primary_key=True, autoincrement=True)
64     server_id = Column(Integer, ForeignKey(\'server.id\'))
65     group_id = Column(Integer, ForeignKey(\'group.id\'))
66 
67 
68 def init_db():
69     """
70     根据类创建数据库表
71     :return:
72     """
73     engine = create_engine(
74         \'mysql+pymysql://root:mysql@127.0.0.1:3306/t1?charset=utf8\',
75         max_overflow=0,  # 超过连接池大小后 最多创建的连接
76         pool_size=3,  # 连接池大小
77         pool_timeout=10,  # 连接池中没有线程最多等待时间，否则报错
78         pool_recycle=-1,  # 多久对线程池进行一次连接回收
79     )
80     Base.metadata.create_all(engine)
81 
82 
83 def drop_db():
84     """
85     根据类删除数据库表
86     :return:
87     """
88     engine = create_engine(
89         \'mysql+pymysql://root:mysql@127.0.0.1:3306/t1?charset=utf-8\',
90         max_overflow=0,
91         pool_size=3,
92         pool_timeout=5,
93         pool_recycle=-1,
94     )
95     Base.metadata.drop_all(engine)

SQLALchemy之创建表

 

 1 from sqlalchemy import create_engine
 2 from sqlalchemy.ext.declarative import declarative_base
 3 from sqlalchemy.sql import text
 4 
 5 Base = declarative_base()
 6 
 7 #  基本增删改查示例
 8 def db_action():
 9     """
10     基本数据库操作
11     :return:
12     """
13     engine = create_engine(
14         \'mysql+pymysql://root:mysql@127.0.0.1:3306/t1?charset=utf8\',
15         max_overflow=0,
16         pool_size=3,
17         pool_timeout=5,
18         pool_recycle=-1,
19     )
20     Session = sessionmaker(bind=engine)
21 
22     session = Session()
23 
24     # 添加操作
25     obj1 = Users(name=\'AABB\')
26     session.add(obj1)
27 
28     session.add_all([
29         Users(name=\'tom\'),
30         Users(name=\'lily\'),
31         Users(name=\'oobb\'),
32     ])
33     session.commit()
34 
35     # 删除操作
36     session.query(Users).filter(Users.id > 2).delete()
37     session.commit()
38 
39     # 修改操作
40     session.query(Users).filter(Users.id > 0).update({"name": "110"})
41     session.query(Users).filter(Users.id > 0).update({Users.name: Users.name + "110"}, synchronize_session=False)
42     session.query(Users).filter(Users.id > 0).update({"age": Users.age + 1}, synchronize_session="evaluate")
43     session.commit()
44 
45     # 查询操作
46     r1 = session.query(Users).all()
47     r2 = session.query(Users.name.label(\'别名\'), Users.email).all()
48     r3 = session.query(Users).filter(Users.name == \'OOBB\').all()
49     r4 = session.query(Users).filter_by(name=\'oobb\').all()
50     r5 = session.query(Users).filter_by(name=\'oobb\').first()
51     r6 = session.query(Users).filter(text("id<:value and name=:name")).params(value=110, name=\'aa\').order_by(
52         Users.id).all()
53     r7 = session.query(Users).from_statement(text("select * from users where name=:name")).params(name=\'oobb\').all()
54 
55     # 常用操作
56     # [条件查询]
57     m1 = session.query(Users).filter_by(name=\'oouu\').all()
58     m2 = session.query(Users).filter(Users.id > 1, Users.name == \'yyuu\').all()
59     m3 = session.query(Users).filter(Users.id.between(1, 5, 2), Users.email == \'[e-mail]\').all()
60     m4 = session.query(Users).filter(Users.id.in_([1, 2, 5])).all()
61     m5 = session.query(Users).filter(~Users.id.in_([2, 3, 4])).all()  # not in
62     m6 = session.query(Users).filter(Users.id.in_(session.query(Users.id).filter_by(name=\'aa\'))).all()
63 
64 
65     from sqlalchemy import and_, or_
66 
67     m7 = session.query(Users).filter(and_(Users.id > 10, Users.name == \'oo\')).all()
68     m8 = session.query(Users).filter(or_(Users.id < 2, Users.email==\'[e-mail]\')).all()
69     m9 = session.query(Users).filter(
70         or_(
71             Users.id < 3,
72             and_(Users.email==\'[e-mail]\', Users.name==\'cc\'),
73             Users.extra !=\'\'
74         )
75     )
76 
77     # 通配符
78     n = session.query(Users).filter(Users.name.like(\'m%\')).all()
79     n1 = session.query(Users).filter(~Users.name.like(\'m%\')).all()
80 
81     # 限制
82     n2 = session.query(Users)[1:5]
83 
84     # 排序
85     n3 = session.query(Users).order_by(Users.id.desc()).all()
86     n4 = session.query(Users).order_by(Users.id.desc(), Users.name.asc()).all()
87 
88     # 跨表查询
89     a = session.query(Hobby, Person).filter(Hobby.id == Person.hobby_id).all()
90     a1 = session.query(Person).join(Hobby).all()
91     a2 = session.query(Person).join(Hobby, isouter=True).all()
92 
93     # 组合查询
94     b = session.query(Person.name).filter(Person.id>2)
95     b1 = session.query(Hobby.caption).filter(Hobby.id<10)
96     result = b.union(b1).all()
97     result2 = b.union_all(b1).all()

SQLAlchemy之最常见的操作示例