四十四：数据库之SQLAlchemy之join实现复杂查询

Posted 2020-11-29 向前走。

 

准备工作

from datetime import datetime

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

# 数据库信息
host = \'127.0.0.1\'
port = \'3306\'
database = \'db_to_sqlalchemy\'
username = \'root\'
password = \'123456\'

# 数据库类型+连接数据库的插件，这里使用的pymysql
DB_URI = f\'mysql+pymysql://{username}:{password}@{host}:{port}/{database}\'

engine = create_engine(DB_URI)  # 创建引擎
Base = declarative_base(engine)  # 使用declarative_base创建基类
session = sessionmaker(engine)()


class User(Base):
    __tablename__ = \'user\'
    id = Column(Integer, primary_key=True, autoincrement=True)
    username = Column(String(50), nullable=False)

    def __repr__(self):
        return f\'username: {self.username}\'


class Article(Base):
    __tablename__ = \'article\'
    id = Column(Integer, primary_key=True, autoincrement=True)
    title = Column(String(50), nullable=False)
    create_time = Column(DateTime, nullable=False, default=datetime.now)
    uid = Column(Integer, ForeignKey(\'user.id\'))
    author = relationship(\'User\', backref=\'article\')

    def __repr__(self):
        return f\'title: {self.title}\'


Base.metadata.drop_all()  # 删除所有表
Base.metadata.create_all()  # 创建表

user1 = User(username=\'user1\')
for x in range(1):
    article = Article(title=f\'title{x}\')
    article.author = user1
    session.add(article)
session.commit()

user2 = User(username=\'user2\')
for x in range(1, 3):
    article = Article(title=f\'title{x}\')
    article.author = user2
    session.add(article)
session.commit()

 

找到所有用户，按照文章数量进行排序

SQL语句实现

SQLAlchemy实现

由于已经使用了外建，所以会自动将User.id与Article.uid关联