Python 操作mysql数据库之 SQLAlchemy

前言：

字段声明类型中，最右边的是数据库中对应的字段，我们依然可以使用，其左边的的 SQLAchemy 则是其自身封装的自定义类型。

本篇不会讲太多的理论知识，因为这个实用性更强，所以通篇全部都是案例，每个案例都会输出对应的 sql , 这样你也能更清晰的明白自己写出的代码最终都转化成什么样的 sql 了。

本篇的最后一个案例是 upsert “存在则更新，不存在则插入”的高级用法。

案例一：创建一个自定义类

数据库结构

1 CREATE TABLE `student` (
2   `id` int(2) NOT NULL AUTO_INCREMENT,
3   `name` char(20) NOT NULL,
4   `code` char(64) NOT NULL,
5   `sex` char(4) NOT NULL,
6   PRIMARY KEY (`id`) USING BTREE
7 ) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8;

数据库中的值

Id   name  code  sex
------------------------------------ 
1    Bob    AU    dddd
2    Bob    BR    girl
3    Hua    CA    boy
4    Lan    CN    girl
5    Hua    RU    girl
6    Smith  US    boy
7    Bob    AU    boy
8    Smith  BM    girl
9    Hub    BU    boy
10    Hip   HK    boy

 1 映射关系
 2 from sqlalchemy import create_engine, Column, INT, VARCHAR
 3 from sqlalchemy.ext.declarative import declarative_base
 4 from sqlalchemy.orm import sessionmaker
 5  
 6  
 7 # 创建引擎 , echo=True ,表示需要开启 sql 打印，调试的以后特别好用
 8 engine = create_engine("mysql+mysqldb://root:[email protected]:3306/yinguohai", pool_size=2, max_overflow=0, echo=True)
 9  
10  
11 # 创建基类，返回一个定制的metaclass 类
12 Base = declarative_base()
13  
14  
15 # 自定义类
16 class Student(Base):
17     # 表名
18     __tablename__ = 'student'
19     # 字段映射
20     id = Column('id', INT, primary_key=True)
21     name = Column('name', VARCHAR)
22     code = Column('code', VARCHAR)
23     sex = Column('sex', VARCHAR)
24  
25  
26     def to_dict(self):
27         """
28         将查询的结果转化为字典类型
29         Student 对象的内容如下 {'_sa_instance_state': <sqlalchemy.orm.state.InstanceState object at 0x10174c898>, 'sex': 'nan', 'name': 'ygh', 'code': 'AU', 'school': 'hua'}
30         获取其值剔除 "_sa_instance_state 即可。但不能在self.__dict__上直接删除”_sa_instance_state” 这个值是公用的。
31         :return:
32         """
33         return {k: v for k, v in self.__dict__.items() if k != "_sa_instance_state”}
34  
35 # 创建会话对象，用于操作数据库
36 Session = sessionmaker(bind=engine)
37 session = Session()

ps: 下面的例子全部是依据这个来

案例二：全部查询

1 result = session.query(Student).all()
2 for i in result:
3     # i是一个Student对象，所以可以使用其 to_dict() 去格式化其对象的值
4     if isinstance(i, Student):
5         print(i.to_dict())

-------------------------结果-------------------------
{'sex': 'dddd', 'name': 'Bob', 'id': 1, 'code': 'AU'}
{'sex': 'girl', 'name': 'Bob', 'id': 2, 'code': 'BR'}
{'sex': 'boy', 'name': 'Hua', 'id': 3, 'code': 'CA'}
{'sex': 'girl', 'name': 'Lan', 'id': 4, 'code': 'CN'}
{'sex': 'girl', 'name': 'Hua', 'id': 5, 'code': 'RU'}
{'sex': 'boy', 'name': 'Smith', 'id': 6, 'code': 'US'}
{'sex': 'boy', 'name': 'Bob', 'id': 7, 'code': 'AU'}
{'sex': 'girl', 'name': 'Smith', 'id': 8, 'code': 'BM'}
{'sex': 'boy', 'name': 'Hub', 'id': 9, 'code': 'BU'}
{'sex': 'boy', 'name': 'Hip', 'id': 10, 'code': 'HK'}

Sql:

1 SELECT
2     student.id AS student_id,
3     student.NAME AS student_name,
4     student.CODE AS student_code,
5     student.sex AS student_sex
6 FROM
7     student

案例三：部分字段查询

1 result = session.query(Student.id, Student.name).all()
2 for i in result:
3     # 此时返回的是一个tuple ,而不是一个Student对象
4     print(i)

-------------------------结果-------------------------
(1, 'Bob')
(2, 'Bob')
(3, 'Hua')
(4, 'Lan')
(5, 'Hua')
(6, 'Smith')
(7, 'Bob')
(8, 'Smith')
(9, 'Hub')
(10, 'Hip')

Sql:

1 SELECT
2     student.id AS student_id,
3     student.NAME AS student_name
4 FROM
5     student

案例四：多条件查询

或， or_

result = session.query(Student).filter( or_(Student.name == "Bob", Student.sex != "aa")). first()

print(result.to_dict())

-------------------------结果-------------------------

{'sex': 'dddd', 'name': 'Bob', 'id': 1, 'code': 'AU'}

Sql:

SELECT

student.id AS student_id,

student.NAME AS student_name,

student.CODE AS student_code,

student.sex AS student_sex

FROM

student

WHERE

student.NAME = % s

OR student.sex != % s ( 'Bob', 'aa', 1 )

且，and_

result = session.query(Student).filter( and_(Student.name == "Bob" , Student.sex != "aa")). first()

print(result.to_dict())

-------------------------结果-------------------------

{'sex': 'dddd', 'name': 'Bob', 'id': 1, 'code': 'AU'}

Sql:

SELECT

student.id AS student_id,

student.NAME AS student_name,

student.CODE AS student_code,

student.sex AS student_sex

FROM

student

WHERE

student.NAME = % s

AND student.sex != % s

LIMIT % s ( 'Bob', 'aa', 1 )

案例五：like , 模糊查询

result = session.query(Student).filter( Student.sex.like('%bo%')). first()

print(result.to_dict())

-------------------------结果-------------------------

{'sex': 'dddd', 'name': 'Bob', 'id': 1, 'code': 'AU'}

Sql:

SELECT

student.id AS student_id,

student.NAME AS student_name,

student.CODE AS student_code,

student.sex AS student_sex

FROM

student

WHERE

student.sex LIKE % s

LIMIT %s ('%bo%', 1)

案例六：in_ , 范围查询

result = session.query(Student).filter( Student.name.in_(["Bob", "Smith"])).all()

for i in result:

print(i.to_dict())

-------------------------结果-------------------------

{'code': 'AU', 'id': 1, 'name': 'Bob', 'sex': 'dddd'}

{'code': 'BR', 'id': 2, 'name': 'Bob', 'sex': 'girl'}

{'code': 'US', 'id': 6, 'name': 'Smith', 'sex': 'boy'}

{'code': 'AU', 'id': 7, 'name': 'Bob', 'sex': 'boy'}

{'code': 'BM', 'id': 8, 'name': 'Smith', 'sex': 'girl'}

Sql:

SELECT

student.id AS student_id,

student.NAME AS student_name,

student.CODE AS student_code,

student.sex AS student_sex

FROM

student

WHERE

student.NAME IN (% s, % s ) ( 'Bob', 'Smith' )

案例七：排序，asc() , desc()

#result = session.query(Student).order_by( Student.id.desc()).all()

result = session.query(Student).order_by( Student.id.asc()).all()

for i in result:

print(i.to_dict())

-------------------------结果-------------------------

{'sex': 'dddd', 'name': 'Bob', 'id': 1, 'code': 'AU'}

{'sex': 'girl', 'name': 'Bob', 'id': 2, 'code': 'BR'}

{'sex': 'boy', 'name': 'Hua', 'id': 3, 'code': 'CA'}

{'sex': 'girl', 'name': 'Lan', 'id': 4, 'code': 'CN'}

{'sex': 'girl', 'name': 'Hua', 'id': 5, 'code': 'RU'}

{'sex': 'boy', 'name': 'Smith', 'id': 6, 'code': 'US'}

{'sex': 'boy', 'name': 'Bob', 'id': 7, 'code': 'AU'}

{'sex': 'girl', 'name': 'Smith', 'id': 8, 'code': 'BM'}

{'sex': 'boy', 'name': 'Hub', 'id': 9, 'code': 'BU'}

{'sex': 'boy', 'name': 'Hip', 'id': 10, 'code': 'HK'}

Sql:

SELECT

student.id AS student_id,

student.NAME AS student_name,

student.CODE AS student_code,

student.sex AS student_sex

FROM

student

ORDER BY

student.id ASC

案例八：分页

方式一 ,limit( position )

result = session.query(Student). limit(2).all()

for i in result:

print(i.to_dict())

-------------------------结果-------------------------

{'sex': 'dddd', 'name': 'Bob', 'id': 1, 'code': 'AU'}

{'sex': 'girl', 'name': 'Bob', 'id': 2, 'code': 'BR'}

Sql:

SELECT

student.id AS student_id,

student.NAME AS student_name,

student.CODE AS student_code,

student.sex AS student_sex

FROM

student

LIMIT % s (2,)

方式二： slice(start, end)

result = session.query(Student).order_by(Student.id.asc()). slice(2, 3).all()

for i in result:

print(i.to_dict())

-------------------------结果-------------------------

{'sex': 'boy', 'code': 'CA', 'id': 3, 'name': 'Hua'}

Sql:

SELECT

student.id AS student_id,

student.NAME AS student_name,

student.CODE AS student_code,

student.sex AS student_sex

FROM

student

ORDER BY

student.id ASC

LIMIT % s,% s ( 2, 1 )

案例九：统计

result = session.query(Student). count()

print(result)

-------------------------结果-------------------------

Sql:

SELECT

count(*) AS count_1

FROM

( SELECT student.id AS student_id, student.NAME AS student_name, student.CODE AS student_code, student.sex AS student_sex FROM student ) AS anon_1

案例十：去重

result = session.query(Student.name). distinct(Student.name).all()

-------------------------结果-------------------------

('Bob',)

('Hua',)

('Lan',)

('Smith',)

('Hub',)

('Hip',)

Sql:

SELECT DISTINCT

student.NAME AS student_name

FROM

student

案例十一：联合查询,默认 inner join查询

result = session.query(Student.id, Student.code, Student.name, Country.population). join(Country, Student.code == Country.code).all()

for i in result:

print(i)

-------------------------结果-------------------------

(1, 'AU', 'Bob', 18886000)

(2, 'BR', 'Bob', 170115000)

(3, 'CA', 'Hua', 1147000)

(4, 'CN', 'Lan', 1277558000)

(5, 'RU', 'Hua', 146934000)

(6, 'US', 'Smith', 278357000)

(7, 'AU', 'Bob', 18886000)

Sql:

SELECT

student.id AS student_id,

student.CODE AS student_code,

student.NAME AS student_name,

a_country.population AS a_country_population

FROM

student

INNER JOIN a_country ON student.CODE = a_country.CODE

案例十二：添加

方式一，单条插入,add( )

result = session.add(Student(name="Bob", code="AU", sex="boy"))

print(result)

#事务需要提交才能生效，有别与查询

session.commit()

Sql:

BEGIN

INSERT INTO student (name, code, sex) VALUES (%s, %s, %s) ('Bob', 'AU', 'boy’)

COMMIT

-------------------------结果-------------------------

None

方式二，批量插入, add_all( )

result = session.add_all([

Student(name="Smith", code="BM", sex="girl"),

Student(name="Hub", code="BU", sex="boy"),

Student(name="Hip", code="HK", sex="boy"),

])

session.commit()

print(result)

-------------------------结果-------------------------

None

Sql:

BEGIN

INSERT INTO student (name, code, sex) VALUES (%s, %s, %s) ('Smith', 'BM', 'girl’)

INSERT INTO student (name, code, sex) VALUES (%s, %s, %s) ('Hub', 'BU', 'boy’)

INSERT INTO student (name, code, sex) VALUES (%s, %s, %s) ('Hip', 'HK', 'boy’)

COMMIT

案例十三：更新

result = session.query(Student).filter(Student.id == 1). update({Student.sex: "dddd”})

# 如果想回滚，则使用 session.rollback() 回滚即可

session.commit()

# 返回修改的记录函数

print(result)

-------------------------结果-------------------------

Sql:

BEGIN

UPDATE student SET sex=%s WHERE student.id = %s ('dddd', 1)

COMMIT

案例十四：不存在则插入，存在则更新

这个属于一种高级的用法，不过也特别简单，看此案例你基本上就秒懂了。

insert_smt = insert(Student).values(id=1, name="bb", code="AA", sex="boy"). on_duplicate_key_update(sex="aaaaa",code="uuuuu")

result = session.execute(insert_smt)

session.commit()

print(result.rowcount)

-------------------------结果-------------------------

注意事项：

需要引入一个特别函数 , insert( ) , 它是mysql包下的。from sqlalchemy.dialects.mysql import insert
使用 on_duplicate_key_update( ) 这个函数进行异常处理，别用错了
使用execute ，执行insert( ) 函数创建的 Sql 语句即可
最后一定要记得 commit( ) 一下。

Sql:

BEGIN

INSERT INTO student ( id, NAME, CODE, sex )

VALUES (% s, % s, % s, % s )

ON DUPLICATE KEY UPDATE code = %s, sex = %s

(1, 'bb', 'AA', 'boy', 'uuuuu', 'aaaaa')

COMMIT

Python 操作mysql数据库之 SQLAlchemy

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