Running cleaning/validation code before committing in sqlalchemy - postgresql

Question

I'm totally new to PostGreSQL and SQLAlchemy, and I'm trying to figure out how to run validation/cleaning code on an SQLAlchemy model before it is committed to the database. The idea is to ensure data consistency beyond the standard type enforcement that comes built into SQL databases. For example, if I have a User model built on SQLAlchemy's models,
class User(db.Model):
...
email = db.Column(db.String())
zipCode = db.Column(db.String())
lat = db.Column(db.Float())
lng = db.Column(db.Float())
...
Before committing this document, I want to:
trim any leading & trailing spaces off the email field
ensure that the zip code is a 5-digit string of numbers (I'll define a regex for this)
automatically look up the corresponding latitude/longitude of the zip code and save those in the lat & lng fields.
other things that a database schema can't enforce
Does SQLAlchemy provide an easy way to provide Python code that is guaranteed to run before committing to do arbitrary tasks like this?

Answer 1

I found the easiest is to hook onto the update and insert events. http://docs.sqlalchemy.org/en/latest/orm/events.html
from sqlalchemy import event
def my_before_insert_listener(mapper, connection, target):
target.email=target.email.trim()
#All the other stuff
# associate the listener function with User,
# to execute during the "before_insert" hook
event.listen(
User, 'before_insert', my_before_insert_listener)
You can create custom sqlalchemy types that do this sort of thing.