python SQLAlchemy的Mapping与Declarative详解

from sqlalchemy import Table, MetaData, Column, Integer, String,
from sqlalchemy.orm import mapper

# 数据库的元数据，你可以认为它是一个容器，装载了所有的表结构
metadata = MetaData()

# 数据库中的news_article表
article = Table("news_article", metadata,
        Column("id", Integer, primary_key=True),
        Column("title", String)
        )

# 这是一个普通的Article类
class Article:
  def __init__(self, title):
    self.title = title

# 通过mapper函数进行映射关联
mapper(Article, article)

from sqlalchemy.orm import sessionmaker
Session = sessionmaker(bind=engine)
session = Session()
# 通过Artcile类来查询id==4554的记录，这完全是用面向对象的方式执行sql了
# 返回结果就是Article的实例对象
result = session.query(Article).filter(Article.id==4554).first()
print(result.id) # 4554
print(result.title) # xxxxxxxxx

from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class Article(Base):
  __tablename__ = 'news_article'
  id = Column(Integer, primary_key=True)
  title = Column(String(50))

> print(Article.__table__)
news_article

>print(Article.__mapper__)
Mapper|Article|news_article

# 前面将的metadata 可以通过 Base 获取
>print(Base.metadata)
MetaData(bind=None)