Day48：SQLALchemy操作MySQL关系型数据库

1.安装sqlalchemy

pip install sqlalchemy；

2.SQLALchemy介绍

可以把model中的模型和数据库中的一行数据相互映射的工具；
将代码中的数据模型与表中的字段一一对应；

3.什么是ORM

ORM（Object Relational Mapper）就是把数据库表的行与相应的对象建立关联，互相转换；
目前，最知名的Python ORM是SQLAlchemy和SQLobject；

4.实体类的创建的两个好处

如果数据库中没有表，那么可以使用实体类创建；
如果数据库中有表，实体类可以映射表的结构，对表的CRUD操作；

5.数据库操作

创建表：create_all()；
删除表：drop_all()，或者是session.delete()；

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String
from sqlalchemy.orm import sessionmaker
Base = declarative_base()
class Teacher(Base):
    __tablename__ = 'teacher'
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String(255))
    age = Column(Integer)
    
    def __repr__(self):
        # print(self.__dict__)
        return "id='%s', name='%s', age='%s" % (self.id, self.name, self.age)
    __str__ = __repr__

# 创建连接引擎
host = 'localhost'
port = 3306
username = 'robby'
password = 'robby123456'
db = 'XKD_Python_Course'
connect_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(connect_str, echo=True)

# 创建表
Base.metadata.create_all(engine)
# 删除表
Base.metadata.drop_all(engine)

插入数据：session.add_all()；

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String
from sqlalchemy.orm import sessionmaker
Base = declarative_base()
class Teacher(Base):
    __tablename__ = 'teacher'
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String(255))
    age = Column(Integer)

    def __repr__(self):
        # print(self.__dict__)
        return "id='%s', name='%s', age='%s" % (self.id, self.name, self.age)
    __str__ = __repr__

# 创建连接引擎
host = 'localhost'
port = 3306
username = 'robby'
password = 'robby123456'
db = 'XKD_Python_Course'
connect_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(connect_str, echo=True)

# 创建会话，用于提交数据
Session = sessionmaker(bind=engine)
session = Session()

# 创建多行行实例，给表添加数据
try:
    lst = []
    for i in range(10):
        teacher = Teacher()
        teacher.name = 'nihao' + str(i)
        teacher.age = 20 + i
        lst.append(teacher)
        print(teacher)
    # session.add(student) 可以添加一行记录，也可以添加多行记录
    # 注意：这里加行记录实例添加到session，不会提交，需要手动提交
    session.add_all(lst) # pendding
except Exception as e:
    print('~~~~~~~~~~~'*200)
    session.rollback()
    print(e)
finally:
    session.commit()

查询操作：session.query()，迭代查询；

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

Base = declarative_base()
class Teacher(Base):
    __tablename__ = 'teacher'
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String(255))
    age = Column(Integer)
    def __repr__(self):
        # print(self.__dict__)
        return "id='%s', name='%s', age='%s" % (self.id, self.name, self.age)
    __str__ = __repr__

host = 'localhost'
port = 3306
username = 'robby'
password = 'robby123456'
db = 'XKD_Python_Course'
conn_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(conn_str, echo=False)

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

teacher_obj = session.query(Teacher)
for teacher in  teacher_obj:
    print(teacher) # 返回结果：{'_sa_instance_state': <sqlalchemy.orm.state.InstanceState object at 0x1063125f8>, 'age': 20, 'name': 'nihao0', 'id': 1}
print('*'*300)

# 直接返回实例对象
teacher = session.query(Teacher).get(4)
print(teacher) # 返回结果：{'_sa_instance_state': <sqlalchemy.orm.state.InstanceState object at 0x1075fd400>, 'age': 23, 'name': 'nihao3', 'id': 4}
print(teacher.id)  # 返回 aobama
print(teacher.name)
print(teacher.age)
print('*'*300)

# 返回的是可迭代对象
teacher_results = session.query(Teacher).filter(Teacher.id == 5)
for teacher in teacher_results:  # 拿到student实例对象
    print(teacher)

修改操作：session.update()；

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

Base = declarative_base()

class Teacher(Base):
    __tablename__ = 'teacher'
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(String(255))
    age = Column(Integer)
    def __repr__(self):
        # print(self.__dict__)
        return "id='%s', name='%s', age='%s" % (self.id, self.name, self.age)
    __str__ = __repr__

# 创建连接引擎
host = 'localhost'
port = 3306
username = 'robby'
password = 'robby123456'
db = 'XKD_Python_Course'
conn_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(conn_str, echo=False)

# 创建会话，用于提交数据
Session = sessionmaker(bind=engine)
session = Session()

teacher = session.query(Teacher).get(4)
teacher.name = 'Robby'
teacher.age = '99'
session.commit()

提交：session.commit()；

6.where条件查询

where条件查询过滤，返回可迭代对象；
AND取与、OR取并、NOT取反、in存在、not in不存在；
like可以忽略大小写进行模式匹配；

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, DATE, Enum, ForeignKey
import enum
from sqlalchemy.orm import sessionmaker
Base = declarative_base()
class My_Enum(enum.Enum):
    M = 'M'
    F = 'F'


# 实体类
class Emploee(Base):
    '''
    +------------+---------------+------+-----+---------+-------+
    | Field      | Type          | Null | Key | Default | Extra |
    +------------+---------------+------+-----+---------+-------+
    | emp_no     | int(11)       | NO   | PRI | NULL    |       |
    | birth_date | date          | NO   |     | NULL    |       |
    | first_name | varchar(14)   | NO   |     | NULL    |       |
    | last_name  | varchar(16)   | NO   |     | NULL    |       |
    | gender     | enum('M','F') | NO   |     | NULL    |       |
    | hire_date  | date          | NO   |     | NULL    |       |
    +------------+---------------+------+-----+---------+-------+
    '''
    __tablename__ = 'employees'
    emp_no = Column(Integer, primary_key=True, nullable=False)
    birth_date = Column(DATE, nullable=False)
    first_name = Column(String(14), nullable=False)
    last_name = Column(String(16),nullable=False)
    gender = Column(Enum(My_Enum), nullable=False)
    hire_date = Column(DATE, nullable=False)
    def __repr__(self):
        return "emp_no='%s', birth_date='%s', first_name='%s', last_name='%s', gender='%s', hire_date='%s'" % (self.emp_no, self.birth_date, self.first_name, self.last_name, self.gender, self.hire_date)
    __str__ = __repr__

# 创建连接引擎
host = 'localhost'
port = 3306
username = 'robby'
password = 'robby123456'
db = 'XKD_Python_Course'
conn_str = 'mysql+mysqldb://{}:{}@{}:{}/{}'.format(username, password, host, port,db)
engine = create_engine(conn_str, echo=False)

# 创建表
Base.metadata.create_all(engine)

# 创建会话，用于提交数据
Session = sessionmaker(bind=engine)
session = Session()


# # 简单的where条件查询过滤， 返回可迭代对象, AND 取与
emploees = session.query(Emploee).filter(Emploee.emp_no < 10010).filter(Emploee.gender == 'M')
emploees = session.query(Emploee).filter((Emploee.emp_no > 10010) & (Emploee.gender == 'F'))

# OR 取并
emploees = session.query(Emploee).filter((Emploee.emp_no > 10010) | (Emploee.gender == 'F'))

# NOT 取反
emploees = session.query(Emploee).filter(~(Emploee.emp_no > 10010))

# in
emploees = session.query(Emploee).filter(Emploee.emp_no.in_([10010, 10011, 10012]))

# not in
emploees = session.query(Emploee).filter(~Emploee.emp_no.in_([10010, 10011, 10012]))

# like ，like可以忽略大小写进行模式匹配
emploees = session.query(Emploee).filter(Emploee.last_name.like('B%'))

for emploee in emploees:
    print(emploee)

7.order排序

asc()：升序；

例如：
emploees = session.query(Emploee).filter(Emploee.last_name.like('B%')).order_by(Emploee.emp_no.asc())

desc()：降序；

例如：
emploees=session.query(Emploee).filter(Emploee.last_name.like('B%')).order_by(Emploee.emp_no.desc())

多字段排序：在语句里面进行多次排序；

8.聚合与分组

list()：转化为列表；
count()：聚合count(*)查询；

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all()：转化为列表；
limit().one()：查询首行；

emploees = session.query(Emploee)
print(list(emploees))         # 转化为列表
print(emploees.count())     # 聚合count(*)查询
print(emploees.all())        # 转化为列表
print(emploees.limit(1).one())    # 查询首行

max()：返回最大值；
min()：返回最小值；
avg()：返回平均值；

emploees = session.query(func.max(Emploee.emp_no))
emploees = session.query(func.min(Emploee.emp_no))
emploees = session.query(func.avg(Emploee.emp_no))

group_by()：分组查询；

emploees = session.query(func.count(Emploee.emp_no)).group_by(Emploee.gender)
print(emploees)
for emploee in emploees:
    print(emploee)

参考：https://www.9xkd.com/user/plan-view.html?id=2415909403

Day48：SQLALchemy操作MySQL关系型数据库

1.安装sqlalchemy

2.SQLALchemy介绍

3.什么是ORM

4.实体类的创建的两个好处

5.数据库操作

6.where条件查询

7.order排序

8.聚合与分组

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