SQLAlchemy: change table schema, on the fly

db.py

# -*- coding: utf-8; -*-

from tigger import app
app.ready()
from tigger import db

def decorate_timestamps():
    from datetime import datetime
    from sqlalchemy import TIMESTAMP, Column, text

    default_create_time_col = \
      Column('create_time', TIMESTAMP,
             nullable=False, default=datetime.now,
             server_default='0000-00-00 00:00:00')
    default_update_time_col = \
      Column('update_time', TIMESTAMP,
             nullable=False, default=datetime.now,
             server_default=text('CURRENT_TIMESTAMP on '\
                                 'update CURRENT_TIMESTAMP'))

    tables = dict(db.metadata.tables)
    for i in tables:
        table = tables[i]
        for col in table.columns:
            if 'update_time' == col.name:
                table.columns.replace(default_update_time_col)
            if 'create_time' == col.name:
                table.columns.replace(default_create_time_col)

with app.app_context(), db.use_bind('master'):
    from tigger import models
    db.drop_all()

    if 'mysql' in db.engine.url.drivername.lower():
        pass
        decorate_timestamps()

    db.create_all()