sqlalchemy 的 ORM 方式使用示例

from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

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)

from sqlalchemy import create_engine

engine = create_engine(‘sqlite:///:memory:‘, echo=True)

from sqlalchemy.orm import Session

session = Session(engine)

Base.metadata.drop_all(engine)
Base.metadata.create_all(engine) # 生产环境只需运行一次！！！！

session.add_all([Parent(children=[Child() for j in range(5)]) for i in range(2)])
session.commit()

# 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

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, ForeignKey
from sqlalchemy.orm import relationship

from sqlalchemy import create_engine
from sqlalchemy.orm import Session

from sqlalchemy.orm import joinedload, subqueryload


# 声明基类
Base = declarative_base()


# 定义表
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)
        
        
# 建立连接
engine = create_engine(‘sqlite:///:memory:‘, echo=True)


# 建立会话
session = Session(engine)


# 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