python SQLAlchemy的Mapping與Declarative詳解

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

# 數(shù)據(jù)庫的元數(shù)據(jù)，你可以認為它是一個容器，裝載了所有的表結(jié)構(gòu)
metadata = MetaData()

# 數(shù)據(jù)庫中的news_article表
article = Table("news_article", metadata,
        Column("id", Integer, primary_key=True),
        Column("title", String)
        )

# 這是一個普通的Article類
class Article:
  def __init__(self, title):
    self.title = title

# 通過mapper函數(shù)進行映射關(guān)聯(lián)
mapper(Article, article)

from sqlalchemy.orm import sessionmaker
Session = sessionmaker(bind=engine)
session = Session()
# 通過Artcile類來查詢id==4554的記錄，這完全是用面向?qū)ο蟮姆绞綀?zhí)行sql了
# 返回結(jié)果就是Article的實例對象
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

# 前面將的metadata 可以通過 Base 獲取
>>>print(Base.metadata)
MetaData(bind=None)