知乎： 使用 sqlalchemy 的 orm 方式操作数据库是一种怎样的体验？
答： 酸爽！
本文基于：win10 + python3.4 + sqlAlchemy 1.0.13
先看一个图（来源）：
这是 sqlalchemy 的层级图。不难发现，其中 orm 是最顶级的封装。
ORM 基本操作步骤如下：
1. 建立连接
from sqlalchemy import create_engine
engine = create_engine('sqlite:///:memory:', echo=True)
2. 建立会话
from sqlalchemy.orm import Session
session = Session(engine)
3. 声明基类
from sqlalchemy.ext.declarative import declarative_base Base = declarative_base()
4. 定义表（继承基类）
from sqlalchemy import Column, Integer, ForeignKey from sqlalchemy.orm import relationship class Parent(Base): __tablename__ = 'parent' id = Column(Integer, primary_key=True) children = relationship("Child") def __repr__(self): return "<Parent(id='{}', children='{}')>".format(self.id, self.children) class Child(Base): __tablename__ = 'child' id = Column(Integer, primary_key=True) parent_id = Column(Integer, ForeignKey('parent.id')) def __repr__(self): return "<Child(id='{}', parent_id='{}')>".format(self.id, self.parent_id)
5. 生成表
Base.metadata.drop_all(engine) Base.metadata.create_all(engine) # 生产环境只需运行一次！！！！
6. 添加记录
session.add_all([Parent(children=[Child() for j in range(5)]) for i in range(2)]) session.commit()
7. 查询
# 懒加载 (lazyload) # load everything, no eager loading. for parent in session.query(Parent): print(parent.children) # 联合加载 (joinedload) # load everything, joined eager loading. for parent in session.query(Parent).options(joinedload("children")): parent.children # 子查询加载 (subqueryload) # load everything, subquery eager loading. for parent in session.query(Parent).options(subqueryload("children")): parent.children
8. 完整代码
from sqlalchemy import create_engine from sqlalchemy.orm import Session from sqlalchemy.ext.declarative import declarative_base from sqlalchemy import Column, Integer, ForeignKey from sqlalchemy.orm import relationship from sqlalchemy.orm import joinedload, subqueryload # 建立连接 engine = create_engine('sqlite:///:memory:', echo=True) # 建立会话 session = Session(engine) # 声明基类 Base = declarative_base() # 定义表（继承基类） class Parent(Base): __tablename__ = 'parent' id = Column(Integer, primary_key=True) children = relationship("Child") def __repr__(self): return "<Parent(id='{}', children='{}')>".format(self.id, self.children) class Child(Base): __tablename__ = 'child' id = Column(Integer, primary_key=True) parent_id = Column(Integer, ForeignKey('parent.id')) def __repr__(self): return "<Child(id='{}', parent_id='{}')>".format(self.id, self.parent_id) # 生成表 Base.metadata.drop_all(engine) Base.metadata.create_all(engine) # 生产环境只需运行一次！！！！ # 添加记录 session.add_all([Parent(children=[Child() for j in range(5)]) for i in range(2)]) session.commit() # 查询 # lazyload # load everything, no eager loading. for parent in session.query(Parent): print(parent.children) # joinedload # load everything, joined eager loading. for parent in session.query(Parent).options(joinedload("children")): parent.children # subqueryload # load everything, subquery eager loading. for parent in session.query(Parent).options(subqueryload("children")): parent.children
