SqlAlchemy的简单使用

1.SQLAlchemy

SQLAlchemy是python的一个通用的ORM框架

1.1 创建数据表

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Integer, String, Column

BaseModel = declarative_base()

 
class User(BaseModel):
    # 定义表名
    __tablename__ = 'user'
    id = Column(Integer, primary_key=True)  # 定义主键字段，如果是int型，就会自动自增
    name = Column(String(32), nullable=False, unique=True)  # 定义字符串非空，唯一字段


# 创建一个引擎连接数据库
from sqlalchemy import create_engine

# 格式：engine = create_engine("postgresql://scott:tiger@localhost/test?charset=utf8")
# "数据库种类+数据库驱动://用户名:密码@IP地址:端口号/数据库名"  端口号不写，使数据库默认端口
engine = create_engine('mysql+pymysql://root:123@127.0.0.1:3306/test')

# 扫描BaseModel下所有的继承它的model,并创建
BaseModel.metadata.create_all(engine)

1.2 增删改查

1.2.1 新增数据

# 导入创建好的model
from models import User

# 创建一个model对象
user = User(name='tom')
# 写入数据库
# 首先要打开数据库会话，相当于创建一个操作数据库的窗口
from sqlalchemy.orm import sessionmaker
# 导入之前创建好的引擎
from models import engine

# 通过数据库引擎创建会话类
Session = sessionmaker(engine)
# 打开会话对象，相当于新建了一个查询窗口
session = Session()
# 在会话中添加一条model数据
session.add(user)
# 提交会话，将会话中的所有数据提交到数据库
session.commit()
# 关闭会话
session.close()

'''
可以一次添加多条数据，然后再提交
session.add(User(name='rose'))
session.add(User(name='jack'))
session.commit()
session.close()

或者使用列表
user_list = [
    User(name='rose'),
    User(name='jack'),
]
session.add_all(user_list)
session.commit()
session.close()
'''

1.2.2 查询数据

from models import User, engine
from sqlalchemy.orm import sessionmaker

Session = sessionmaker(engine)
session = Session()
# 查询所有的数据
user_list = session.query(User).all()
for user in user_list:
    print(user.name)

# 根据条件查询
user_list = session.query(User).filter(User.id > 1).all()
for user in user_list:
    print(user.id, user.name)
#对于等于的条件要用双等号
user = sessiom.query(User).filter(User.id==3).first()
#或使用filter_by
user = session.query(User).filter_by(User.id=3).first()
    
# 也可以取出一个
user = session.query(User).filter(User.id > 1).first()
print(user.id, user.name)

# 通过all()和first()取出数据，如果不取出数据返回的是原生的sql
sql = session.query(User).filter(User.id > 1)
print(sql)
'''
SELECT user.id AS user_id, user.name AS user_name 
FROM user 
WHERE user.id > %(id_1)s
'''

session.close()

1.2.3 修改数据

from models import User, engine
from sqlalchemy.orm import sessionmaker

Session = sessionmaker(engine)
session = Session()

# 要修改数据首先要查询到数据，然后再对其进行修改
res = session.query(User).filter(User.id == 1).update({'name': 'tree'})
print(res)  # 返回修改的条数
session.commit()  # 增删改都要提交后，才会对数据库数据进行修改
session.close()

1.2.4 删除数据

from models import User, engine
from sqlalchemy.orm import sessionmaker

Session = sessionmaker(engine)
session = Session()

# 要删除数据首先要查询到数据，然后再对其进行修改
res = session.query(User).filter(User.id == 1).delete()
print(res)  # 返回删除的条数
session.commit()  # 增删改都要提交后，才会对数据库数据进行修改
session.close()

1.3 高级查询

from models import User, engine
from sqlalchemy.orm import sessionmaker

Session = sessionmaker(engine)
session = Session()

# 根据多条件查询
from sqlalchemy.sql import and_, or_, text

Users = session.query(User).filter(and_(User.id >= 1, User.name == 'rose')).all()
print(Users)
Users = session.query(User).filter(or_(User.id >= 1, User.name == 'rose')).all()
print(Users)

# 指定查询数据列，和别名
Users = session.query(User.name.label('user_name')).all()
print(Users)  # [('jack',), ('rose',)]
for user in Users:
    print(user.user_name)  # 需要用别名来取

# 表达式筛选条件
Users = session.query(User).filter(User.id == 2).all()
print(Users)
# 原生sql筛选条件
Users = session.query(User).filter_by(id=2).all()
print(Users)
# 字符串方式方式筛选条件，并使用 order_by进行排序
Users = session.query(User).filter(text("id<:value and name=:name")).params(value=7, name='aaa').order_by(
    User.id).all()
print(Users)

1.4 一对多创建

from sqlalchemy.ext import declarative
from sqlalchemy.engine import create_engine
from sqlalchemy import Column, String, Integer, ForeignKey
from sqlalchemy.orm import relationship

BaseModel = declarative.declarative_base()
engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/test?charset=utf8")


class School(BaseModel):
    __tablename__ = "school"
    id = Column(Integer, primary_key=True)
    name = Column(String(32), unique=True)


class Student(BaseModel):
    __tablename__ = "student"
    id = Column(Integer, primary_key=True)
    name = Column(String(32), unique=True)
    sch_id = Column(Integer, ForeignKey("school.id"))

    school = relationship("School", backref="student")


BaseModel.metadata.create_all(engine)

1.5 一对多的CURD

#增加数据
#方式一（和ORM无关系）：先建立一个学校，再查询这个学校的id，根据这个id去创建学生并添加sch_id
#方式二：通过relationship 正向添加
stu = Student(name='张三', school=School(name="清华大学"))
session.add(stu)
session.commit()
session.close()
#方式三：通过relationship反向添加
sch = School(name="北京大学")
sch.student = [
    Student(name="李四"),
    Student(name="王五")
]
session.add(sch)
session.commit()
session.close()

#删除数据，和单表删除一样，但若是学校被引用则无法删除

#查询数据
#正向查询
stu_list = session.query(Student).all()
for stu in stu_list:
    print(stu.name, stu.school.name)
#反向查询
school_list = session.query(School).all()
for school in school_list:
    #print(school.name,len(school.student))  查询每个学校的学生个数
    for stu in school.student:
        print(school.name, stu.name)

1.6 多对多创建

from sqlalchemy.ext import declarative
from sqlalchemy.engine import create_engine
from sqlalchemy import Column, String, Integer, ForeignKey
from sqlalchemy.orm import relationship

BaseModel = declarative.declarative_base()
engine = create_engine("mysql+pymysql://root:123@127.0.0.1:3306/test?charset=utf8")


class Girl(BaseModel):
    __tablename__ = "girl"
    id = Column(Integer, primary_key=True)
    name = Column(String(32), unique=True)

    boy = relationship("Boy", backref="girl", secondary="hotel")  # secondary指定第三张表


class Boy(BaseModel):
    __tablename__ = "boy"
    id = Column(Integer, primary_key=True)
    name = Column(String(32), unique=True)


class Hotel(BaseModel):
    __tablename__ = 'hotel'
    id = Column(Integer, primary_key=True)
    gid = Column(Integer, ForeignKey("girl.id"))
    bid = Column(Integer, ForeignKey("boy.id"))


BaseModel.metadata.create_all(engine)

1.7 多对多的CRUD

from sqlalchemy.orm import sessionmaker
from createM2M import engine,Girl,Boy

Session = sessionmaker(engine)
session = Session()

# 添加数据
# 正向添加
girl = Girl(name='小红', boy=[Boy(name="小明"), Boy(name="小王")])
session.add(girl)
session.commit()
session.close()
#反向添加数据
boy = Boy(name='小李')
boy.girl = [
    Girl(name="小丽"),
    Girl(name="小花")
]
session.add(boy)
session.commit()
session.close()

#查询
#正向查询
res = session.query(Girl).all()
for i in res:
    print(i.name, len(i.boy))
#反向查询
res = session.query(Boy).all()
for i in res:
    print(i.name, len(i.girl))