String column with Sequence breaks identity map

[Former user]

I'm trying to create a class with an id of type 'str' that autoincrements by default (e.g. '1', '2', etc). I gave its corresponding table a String column with an associated Sequence.

If I save an instance, its id is populated with a long, but if I then retrieve the instance from the database, an object with an id of type 'str' is (correctly) returned. This causes the session's identity map lookup to fail.

[Mike Bayer]

sequences are often executed "inline" with a SQL INSERT statement (as of 0.4), so any python-side conversion to string is not portable (also, sequences are specifically for integers so i dont favor any new bells and whistles within Sequence). instead, do the conversion yourself with a pre-executed default (0.4 example):

def mydefault(ctx):
    conn = ctx.connection
    next = conn.execute(Sequence('my_sequence'))
    return str(next)

t = Table('mytable', meta, 
    Column('my_sequence_col', String(30), default=mydefault, primary_key=True)
)