Sqlalchemy: avoiding multiple inheritance and having abstract base class

Question

So I have a bunch of tables using SQLAlchemy that are modelled as objects which inherit from the result to a call to declarative_base(). Ie:

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Answer 1

It is pretty straigh-forward, you just make declarative_base() to return a Base class which inherits from your CommonBase using cls= parameter. Also shown in Augmenting The Base docs. Your code might then look similar to below:

class CommonBase(object):
    @classmethod
    def somecommonaction(cls):
        # body here

Base = declarative_base(cls=CommonBase)

class Table1(Base):
    # __tablename__ & Table1 specific fields here

class Table2(Base):
     # __tablename__ & Table2 specific fields here

Answer 2

SQLAlchemy version 0.7.3 introduced the __abstract__ directive which is used for abstract classes that should not be mapped to a database table, even though they are subclasses of sqlalchemy.ext.declarative.api.Base. So now you create a base class like this:

Base = declarative_base()

class CommonRoutines(Base):
    __abstract__ = True

    id = Column(Integer, primary_key=True)

    def __init__(self):
        # ...

Notice how CommonRoutines doesn't have a __tablename__ attribute. Then create subclasses like this:

class Foo(CommonRoutines):
    __tablename__ = 'foo'

    name = Column(...)

    def __init__(self, name):
        super().__init__()
        self.name = name
        # ...

This will map to the table foo and inherit the id attribute from CommonRoutines.

Source and more information: http://docs.sqlalchemy.org/en/rel_0_7/orm/extensions/declarative.html#abstract

Answer 3

You can use AbstractConcreteBase to make an absract base model:

from sqlalchemy.ext.declarative import AbstractConcreteBase


class AbstractTable(AbstractConcreteBase, Base):
    id = db.Column(db.Integer, primary_key=True)

    @classmethod
    def somecommonaction(cls):
        # body here