如何扩充SQLAlchemy中的声明式基础

Question

I am following the SQLAlchemy Documentation by Mike Bayer and have a couple of issues when trying to augment the declarative_base as per code below.

module db.base

from sqlalchemy.ext.declarative import declared_attr
from sqlalchemy import Column, Date, Integer, String

class Base(object):
    @classmethod
    @declared_attr
    def __tablename__(cls):
        print(">>__tablename__() "+str(cls.__name__.lower()))
        return cls.__name__.lower()
    id = Column(Integer, primary_key=True, nullable = False)
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base(cls=Base)

module db.dbtest

from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session, sessionmaker
from db.base import Base
engine = create_engine('sqlite:////tmp/test.db', echo=True)
db_session = scoped_session(sessionmaker(autocommit=False,
                                autoflush=False,
                                bind=engine))

def init_db():
    import db.model.testdata 
    base = Base()
    base.metadata.create_all(bind=engine)

if __name__ == '__main__':
   init_db()

module db.model.testdata

from db.base import Base
from sqlalchemy import Boolean, Column, Date, Integer, String
from sqlalchemy import REAL

class TestData(Base):
    name = Column(String(255), nullable = False)
    creationDate =  Column(Date, index=True)
    updateDate =  Column(Date, index=True)
    miscData = Column(REAL, nullable = True)

In the SQLAlchemy documentation the @classmethod annotation is not added to the tablename method in the Base class. However without it I get a "Method 'tablename - db.base' should have self as first parameter" error, basically saying that the @declared_attr is not marking the method as a class level method. Are you supposed to add @classmethod or is this a bug in the version (0.9.8) I am using?

The tablename returned by the base augmentor is cryptic "bound method DeclarativeMeta.? of class db.model.testdata.TestData" How can I get just the class name (TestData) returned?

Another minor issue - the print() call in the tablename method in the Base class does not print anything (neither did logger) and I am not sure why.

Answer 1

The reason I was getting a cryptic table name generated and why the print call wasn't working was that the tablename method in the Base class was not being called (due to having the @classmethod annotation).

The issue appears to be with PyDev. I ran the same code in PyCharm, PyCharm did not have an issue with the @declared_attr annotation and did not require @classmethod.

In PyDev, I added sqlalchemy to the forced builtins (Window ->Preferences ->PyDev ->Interpreters ->Python interpreter ->Forced Builtins). I then removed the @classmethod anotation and re-ran it. I still get an 'Method tablename - db.base should have self as first parameter' error marker on the code but it runs OK now.

Answer 2

I still get an 'Method tablename - db.base should have self as first parameter' error marker on the code but it runs OK now.

If that bothers you, having the cursos over the error pointed by PyDev, you can press Control+1 and mark the line as # @NoSelf . This informs PyDev that your method does not have self as its first parameter.