Django: set database level defaults with postgresql_psycopg2 from the model file.

django_db_defaults.py

def db_default(field, db_default):
    """
    Set attribute __db_default for signal to set default values with.
    """
    if db_default == '':
        db_default = "''"
    field.__db_default = db_default
    return field


class OrderShipLog(models.Model):
    """
    This log will have read/write access from pg_endicia.
    """

    date_created = db_default(models.DateTimeField(auto_now_add=True), 'false')
    transaction_datetime = db_default(models.DateTimeField(blank=True, auto_now_add=True), 'now()')
    # perfect example: auto_now_add only works from a django object, not any other SQL insert.


def generate_default_sql(model):
    """
    Generate SQL for postgresql_psycopg2 default values because the shipping
    database post doesn't guarantee posting certain fields but id like them all to be strings.
    """
    db_fields = filter(lambda x: hasattr(x, '__db_default'), model._meta.fields)
    db_table = model._meta.db_table
    modelname = model._meta.object_name

    sql_dir = os.path.join(os.path.dirname(__file__), 'sql/')
    sql_filename = os.path.join(sql_dir, '{modelname}.postgresql_psycopg2.sql'.format(
        modelname=modelname.lower()))
    if not os.path.exists(sql_filename):
        try:
            if not os.path.exists(sql_dir):
                os.makedirs(sql_dir)
            
            with open(sql_filename, 'w+') as f:
                for field in db_fields:
                    attname, db_column = field.get_attname_column()
                    if not field.__db_default:
                        raise Exception("Must enter value for field {modelname}.{field}.__db_default".format(
                            modelname=modelname,
                            field=attname))
                    f.write('ALTER TABLE {db_table} ALTER COLUMN {db_column} SET DEFAULT {default};\n'.format(
                        db_table=db_table,
                        db_column=db_column,
                        default=field.__db_default,
                        ))
        except Exception, e:
            print >> sys.stderr, "Could not generate SQL file. Manually set the defaults! {0}\n".format(e) * 10
generate_default_sql(OrderShipLog)