安装
pip install -i https://pypi.douban.com/simple sqlalchemy
ModuleNotFoundError: No module named 'MySQLdb'。由于sqlalchemy建立在 DB API之上，使用关系对象映射进行数据库操作,缺少依赖模块，安装即可。
Windows系统
pip install -i https://pypi.douban.com/simple mysqlclient
Linux系统
pip install -i https://pypi.douban.com/simple PyMySQL
使用
1. 创建数据表
文件名：model.py
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, ForeignKey
# 通过declarative_base()功能创建一个基类
Base = declarative_base()
# 定义三个表，student表，course表和sc表，以及对应的字段
class Student(Base):
__tablename__ = 'student'
Sno = Column(String, primary_key=True)
Sname = Column(String)
Ssex = Column(String)
Sage = Column(Integer)
Sdept = Column(String)
S_entrance = Column(String)
def __repr__(self):
return "Sno {}".format(self.Sno)
def to_json(self):
diction = self.__dict__
if "_sa_instance_state" in diction:
del diction["_sa_instance_state"]
return diction
class SC(Base):
__tablename__ = 'sc'
Sno = Column(String, ForeignKey('student.Sno'), primary_key=True)
Cno = Column(String, ForeignKey('course.Cno'), primary_key=True)
Grade = Column(Integer)
def __repr__(self):
return "Sno {}".format(self.Sno)
def to_json(self):
diction = self.__dict__
if "_sa_instance_state" in diction:
del diction["_sa_instance_state"]
return diction
class Course(Base):
__tablename__ = 'course'
Cno = Column(String, primary_key=True)
Cname = Column(String)
Cpno = Column(String, ForeignKey('course.Cno'))
Ccredit = Column(Integer)
def __repr__(self):
return "Cno {}".format(self.Cno)
def to_json(self):
diction = self.__dict__
if "_sa_instance_state" in diction:
del diction["_sa_instance_state"]
return diction
2. 数据库连接
文件名：config.py
from sqlalchemy import create_engine
# 通过create_engine()返回一个Engine的实例
engine = create_engine("mysql://root:admin123@127.0.0.1:3306/school")
3. 创建会话session
文件名：config.py
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
engine = create_engine("mysql://root:admin123@127.0.0.1:3306/school")
# 这个定制的Session类会创建绑定到数据库的Session对象。
Session = sessionmaker(bind=engine)
4.数据库查询数据
- 使用all()，返回一个列表
- 使用first(),返回一个结果
- 使用one(),返回且仅返回一个查询结果。当结果的数量不足一个或者多于一个时会报错。
- 使用count(),计数
文件名：dbsession.py
1. 单表查询
查询学生表所有数据
from config import Session
from model import Student
def get_all_student_data():
# 创建一个实例
session = Session()
result_list = session.query(Student).all()
results = [result.to_json() for result in result_list]
# 关闭session
session.close()
return results
运行该函数，结果输出：
[{'S_entrance': datetime.date(2019, 8, 6), 'Sage': 20, 'Sname': 'liyong', 'Sno': '201915121', 'Sdept': 'CS', 'Ssex': 'male'}, {'S_entrance': datetime.date(2019, 8, 6), 'Sage': 19, 'Sname': 'liuchen', 'Sno': '201915122', 'Sdept': 'CS', 'Ssex': 'female'}, {'S_entrance': datetime.date(2019, 8, 6), 'Sage': 18, 'Sname': 'wangming', 'Sno': '201915123', 'Sdept': 'MA', 'Ssex': 'female'}, {'S_entrance': datetime.date(2019, 8, 6), 'Sage': 19, 'Sname': 'zhangli', 'Sno': '201915125', 'Sdept': 'IS', 'Ssex': 'male'}]
使用filter或filter_by进行查询
def get_student_data():
session = Session()
result_list = session.query(Student).filter(Student.Sage == 20).all()
# result_list = session.query(Student).filter_by(Sage=20).all()
results = [result.to_json() for result in result_list]
session.close()
return results
order_by
result_list = session.query(Student).order_by(Student.Sage.desc()).all()
result_list = session.query(Student).order_by(Student.Sage.desc(), Student.Sdept.asc()).all()
group_by
result_list = session.query(Student).group_by(Student.Ssex).all()
通配符
result_list = session.query(Student).filter(Student.Sname.like('li%')).all()
in
result_list = session.query(Student).filter(Student.Sdept.in_(['CS', 'IS'])).all()
not in
result_list = session.query(Student).filter(~Student.Sdept.in_(['CS', 'IS'])).all()
startswith
result_list = session.query(Student).filter(Student.Sno.startswith('1')).all()
endswith
result_list = session.query(Student).filter(Student.Sno.endswith('1')).all()
contains
result_list = session.query(Student).filter(Student.Sno.contains('1')).all()
and
from sqlalchemy import and_
result_list = session.query(Student).filter(and_(Student.Ssex == 'female', Student.Sage == 18)).all()
or
from sqlalchemy import or_
result_list = session.query(Student).filter(or_(Student.Ssex == 'female', Student.Sage == 18)).all()
between
result_list = session.query(Student).filter(Student.Sage.between(16, 18)).all()
2. 联表查询
result_list = session.query(Student, SC).filter(Student.Sno == SC.Sno).filter(Student.Sage == 20).all()
5. 数据库新增数据
import datetime
from config import Session
from model import Student
def add_student_data():
session = Session()
student = Student(S_entrance=datetime.datetime.now(), Sno='201915126', Sname='caixukun', Ssex='male', Sage=18,
Sdept='CS')
session.add(student)
# 一定要commit，不然不会新增数据
session.commit()
session.close()
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6. 数据库修改数据
from config import Session
from model import Student
def set_student_data():
session = Session()
student = session.query(Student).filter(Student.Sname == 'caixukun').first()
student.Sage = 19
session.commit()
session.close()
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7. 数据库删除数据
from config import Session
from model import Student
def del_student_data():
session = Session()
student = session.query(Student).filter(Student.Sname == 'caixukun').first()
session.delete(student)
session.commit()
session.close()
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