How do you get SQLAlchemy to override MySQL "on update CURRENT_TIMESTAMP"

Question

I've inherited an older database that was setup with a "on update CURRENT_TIMESTAMP" put on a field that should only describe an item's creation. With PHP I have been using "timestamp=timestamp" on UPDATE clauses, but in SQLAlchemy I can't seem to force the system to use the set timestamp.

Do I have no choice and need to update the MySQL table (millions of rows)?

foo = session.query(f).get(int(1))
ts = foo.timestamp
setattr(foo, 'timestamp', ts)
setattr(foo, 'bar', bar)
www_model.www_Session.commit()

I have also tried:

foo = session.query(f).get(int(1))
setattr(foo, 'timestamp', foo.timestamp)
setattr(foo, 'bar', bar)
www_model.www_Session.commit()

Answer 1

SQLAlchemy doesn't try to set the field because it thinks the value hasn't changed.

You can tell SQLAlchemy to reassign the value by specifying the onupdate attribute on the Column:

 Column('timestamp', ..., onupdate=literal_column('timestamp'))

This will result in SQLAlchemy automatically adding timestamp=timestamp to all update queries.

If you need to do it one off on an instance, you can assign the column to it:

foo.timestamp = literal_column('timestamp')
# or 
foo.timestamp = foo_tbl.c.timestamp