我是SQLAlchemy的新手(使用Python 3),发现以下令人困惑的地方。在我的简单示例中,在单独的文件中定义了2个模型类,它们之间具有关联关系。
设置正确吗?我的代码要求Animal.py
导入Owner
,因为已定义了关系,否则app/main.py
将引发有关未找到Owner
类的错误。但是,official docs和其他在线示例似乎并未导入当前类所关联的其他类。
具有model/__init__.py
对我的情况有用吗?如果是这样,它将用于什么用途?看到an example that used a __init__.py
file。
Github存储库:__init__.py
文件结构
https://github.com/nyxynyx/sqlalchemy-class-import-error
app / main.py
models / foo / Animal.py
import sys
sys.path.append('..')
from lib.db import db_session
from models.foo.Animal import Animal
if __name__ == '__main__':
print(Animal.query.all())
models / Foo / Owner.py
from sqlalchemy import *
from sqlalchemy.orm import relationship
from ..Base import Base
from .Owner import Owner <-------------- !!!!! if not imported, error occurs when running main.py !!!!!
class Animal(Base):
__tablename__ = 'animals'
id = Column(Integer, primary_key=True)
name = Column(Text)
owner_id = Column(Integer, ForeignKey('owners.id'))
owner = relationship('Owner')
lib / db.py
from sqlalchemy import *
from ..Base import Base
class Owner(Base):
__tablename__ = 'owners'
id = Column(Integer, primary_key=True)
name = Column(Text)
the Animal.py很好。问题是,如果从不导入owner.py,则sqlalchemy永远不会看到Owner模型/表,因此它永远不会将其注册到Base元数据中。您可以通过
将Owner的进口从animal.py删除到main.py中。import json
from sqlalchemy.orm import scoped_session, sessionmaker
from sqlalchemy import create_engine
with open('../settings.json') as f:
settings = json.load(f)
user, password, host, port, dbname = settings['db']['user'], settings['db']['password'], settings['db']['host'], settings['db']['port'], settings['db']['dbname']
connection_url = f'postgresql://{user}:{password}@{host}:{port}/{dbname}'
engine = create_engine(connection_url)
Session = sessionmaker(autocommit=False, autoflush=False, bind=engine)
db_session = scoped_session(Session)
在保留单独的模型文件的同时查看它的工作。