Features

• Creates versions for inserts, deletes and updates

• Does not store updates which don’t change anything

• Supports alembic migrations

• Can revert objects data as well as all object relations at given transaction even if the object was deleted

• Transactions can be queried afterwards using SQLAlchemy query syntax

• Query for changed records at given transaction

• Temporal relationship reflection. Version object’s relationship show the parent objects relationships as they where in that point in time.

• Supports native versioning for PostgreSQL database (trigger based versioning)

QuickStart

pip install SQLAlchemy-Continuum

In order to make your models versioned you need two things:

1. Call make_versioned() before your models are defined.

2. Add __versioned__ to all models you wish to add versioning to

import sqlalchemy as sa
from sqlalchemy_continuum import make_versioned


make_versioned(user_cls=None)


class Article(Base):
    __versioned__ = {}
    __tablename__ = 'article'

    id = sa.Column(sa.Integer, primary_key=True, autoincrement=True)
    name = sa.Column(sa.Unicode(255))
    content = sa.Column(sa.UnicodeText)


article = Article(name='Some article', content='Some content')
session.add(article)
session.commit()

# article has now one version stored in database
article.versions[0].name
# 'Some article'

article.name = 'Updated name'
session.commit()

article.versions[1].name
# 'Updated name'


# lets revert back to first version
article.versions[0].revert()

article.name
# 'Some article'

For completeness, below is a working example.

from sqlalchemy_continuum import make_versioned
from sqlalchemy import Column, Integer, Unicode, UnicodeText, create_engine
from sqlalchemy.orm import Session, configure_mappers, declarative_base

make_versioned(user_cls=None)

Base = declarative_base()
class Article(Base):
    __versioned__ = {}
    __tablename__ = 'article'
    id = Column(Integer, primary_key=True, autoincrement=True)
    name = Column(Unicode(255))
    content = Column(UnicodeText)

configure_mappers()
engine = create_engine('sqlite://')
Base.metadata.create_all(engine)
session = Session(engine)

article = Article(name='Some article', content='Some content')
session.add(article)
session.commit()
article.versions[0].name
article.name = 'Updated name'
session.commit()
article.versions[1].name
article.versions[0].revert()
article.name

Resources

• Documentation

• Issue Tracker

• Code

More information

• http://en.wikipedia.org/wiki/Slowly_changing_dimension

• http://en.wikipedia.org/wiki/Change_data_capture

• http://en.wikipedia.org/wiki/Anchor_Modeling

• http://en.wikipedia.org/wiki/Shadow_table

• https://wiki.postgresql.org/wiki/Audit_trigger

• https://wiki.postgresql.org/wiki/Audit_trigger_91plus

• http://kosalads.blogspot.fi/2014/06/implement-audit-functionality-in.html

• https://github.com/2ndQuadrant/pgaudit