Question

I have an SQLAlchemy ORM class, linked to MySQL, which works great at saving the data I need down to the underlying table. However, I would like to also save the identical data to a second archive table.

Here’s some psudocode to try and explain what I mean

my_data = Data() #An ORM Class
my_data.name = "foo"

#This saves just to the 'data' table
session.add(my_data)

#This will save it to the identical 'backup_data' table
my_data_archive = my_data
my_data_archive.__tablename__ = 'backup_data'
session.add(my_data_archive)

#And commits them both
session.commit()

Just a heads up, I am not interested in mapping a class to a JOIN, as in: http://www.sqlalchemy.org/docs/05/mappers.html#mapping-a-class-against-multiple-tables

Answer 1

I list some options below. I would go for the DB trigger if you do not need to work on those objects in your model.

• use database trigger to do this job for you
• create a SessionExtension which will create and add to session copy-objects (usually on before_flush). Edit-1: You can take versioning example from SA as a basic; this code is doing even more then you need.
• see SA Versioning example which will not only give you a copy of the object, but the whole version history, which might be what you wish for
• see Reverse mapping from a table to a model in SQLAlchemy question, where the proposed solution is described in the blogpost.