在项目开发过程中,会遇到很多数据之间多对多关系的情况,比如:
所以在开发过程中需要使用 ORM 模型将表与表的多对多关联关系使用代码描述出来。多对多关系描述有一个唯一的点就是:需要添加一张单独的表去记录两张表之间的对应关系
主键(id) | 学生名(name) |
---|---|
1 | 张三 |
2 | 李四 |
3 | 王五 |
主键(id) | 本文名(name) |
---|---|
1 | 物理 |
2 | 化学 |
3 | 生物 |
主键(student.id) | 主键(course.id) |
---|---|
1 | 2 |
1 | 3 |
2 | 2 |
3 | 1 |
3 | 2 |
3 | 3 |
tb_student_course = db.Table('tb_student_course',
db.Column('student_id', db.Integer, db.ForeignKey('students.id')),
db.Column('course_id', db.Integer, db.ForeignKey('courses.id'))
)
class Student(db.Model):
__tablename__ = "students"
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(64), unique=True)
courses = db.relationship('Course', secondary=tb_student_course,
backref='student',
lazy='dynamic')
class Course(db.Model):
__tablename__ = "courses"
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(64), unique=True)
if __name__ == '__main__':
db.drop_all()
db.create_all()
# 添加测试数据
stu1 = Student(name='张三')
stu2 = Student(name='李四')
stu3 = Student(name='王五')
cou1 = Course(name='物理')
cou2 = Course(name='化学')
cou3 = Course(name='生物')
stu1.courses = [cou2, cou3]
stu2.courses = [cou2]
stu3.courses = [cou1, cou2, cou3]
db.session.add_all([stu1, stu2, stu2])
db.session.add_all([cou1, cou2, cou3])
db.session.commit()
app.run(debug=True)
首先要在虚拟环境中安装Flask-Migrate。
pip install flask-migrate
#coding=utf-8
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate,MigrateCommand
from flask_script import Shell,Manager
app = Flask(__name__)
manager = Manager(app)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://root:mysql@127.0.0.1:3306/Flask_test'
app.config['SQLALCHEMY_COMMIT_ON_TEARDOWN'] = True
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True
db = SQLAlchemy(app)
#第一个参数是Flask的实例,第二个参数是Sqlalchemy数据库实例
migrate = Migrate(app,db)
#manager是Flask-Script的实例,这条语句在flask-Script中添加一个db命令
manager.add_command('db',MigrateCommand)
#定义模型Role
class Role(db.Model):
# 定义表名
__tablename__ = 'roles'
# 定义列对象
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(64), unique=True)
user = db.relationship('User', backref='role')
#repr()方法显示一个可读字符串,
def __repr__(self):
return 'Role:'.format(self.name)
#定义用户
class User(db.Model):
__talbe__ = 'users'
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(64), unique=True, index=True)
#设置外键
role_id = db.Column(db.Integer, db.ForeignKey('roles.id'))
def __repr__(self):
return 'User:'.format(self.username)
if __name__ == '__main__':
manager.run()
#这个命令会创建migrations文件夹,所有迁移文件都放在里面。
python database.py db init
python database.py db migrate -m 'initial migration'
python database.py db upgrade
可以根据history命令找到版本号,然后传给downgrade命令:
python app.py db history
输出格式:<base> -> 版本号 (head), initial migration
python app.py db downgrade 版本号
以下罗列了使用关系型数据库中常见关系定义模板代码
class Role(db.Model):
"""角色表"""
__tablename__ = 'roles'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(64), unique=True)
users = db.relationship('User', backref='role', lazy='dynamic')
class User(db.Model):
"""用户表"""
__tablename__ = 'users'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(64), unique=True, index=True)
tb_student_course = db.Table('tb_student_course',
db.Column('student_id', db.Integer, db.ForeignKey('students.id')),
db.Column('course_id', db.Integer, db.ForeignKey('courses.id'))
)
class Student(db.Model):
__tablename__ = "students"
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(64), unique=True)
courses = db.relationship('Course', secondary=tb_student_course,
backref=db.backref('students', lazy='dynamic'),
lazy='dynamic')
class Course(db.Model):
__tablename__ = "courses"
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(64), unique=True)
class Comment(db.Model):
"""评论"""
__tablename__ = "comments"
id = db.Column(db.Integer, primary_key=True)
# 评论内容
content = db.Column(db.Text, nullable=False)
# 父评论id
parent_id = db.Column(db.Integer, db.ForeignKey("comments.id"))
# 父评论(也是评论模型)
parent = db.relationship("Comment", remote_side=[id],
backref=db.backref('childs', lazy='dynamic'))
# 测试代码
if __name__ == '__main__':
db.drop_all()
db.create_all()
com1 = Comment(content='我是主评论1')
com2 = Comment(content='我是主评论2')
com11 = Comment(content='我是回复主评论1的子评论1')
com11.parent = com1
com12 = Comment(content='我是回复主评论1的子评论2')
com12.parent = com1
db.session.add_all([com1, com2, com11, com12])
db.session.commit()
app.run(debug=True)
tb_user_follows = db.Table(
"tb_user_follows",
db.Column('follower_id', db.Integer, db.ForeignKey('info_user.id'), primary_key=True), # 粉丝id
db.Column('followed_id', db.Integer, db.ForeignKey('info_user.id'), primary_key=True) # 被关注人的id
)
class User(db.Model):
"""用户表"""
__tablename__ = "info_user"
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(32), unique=True, nullable=False)
# 用户所有的粉丝,添加了反向引用followed,代表用户都关注了哪些人
followers = db.relationship('User',
secondary=tb_user_follows,
primaryjoin=id == tb_user_follows.c.followed_id,
secondaryjoin=id == tb_user_follows.c.follower_id,
backref=db.backref('followed', lazy='dynamic'),
lazy='dynamic')
原创声明:本文系作者授权腾讯云开发者社区发表,未经许可,不得转载。
如有侵权,请联系 cloudcommunity@tencent.com 删除。
原创声明:本文系作者授权腾讯云开发者社区发表,未经许可,不得转载。
如有侵权,请联系 cloudcommunity@tencent.com 删除。