python - Using a SQLAlchemy Integer field to create a timedelta object for comparison -

i have object called item. has 2 fields: datetime row called "created_on," , integer row called "days."

i want query objects created "days" many days ago.

here's how thought should done:

now = utcnow() session.query(item).filter(item.created_on + interval(timedelta(days=item.days)) <= now) 

but i'm unable create timedelta this. i'm getting error:

typeerror: unsupported type timedelta minutes component: instrumentedattribute 

update:

thanks van, should using built-in function. i'm using mysql 5.1, timestampadd. new query this:

now = utcnow() session.query(item).filter(func.timestampadd('day', item.days, item.created_on) <= now) 

however, new error i'm getting is:

"you have error in sql syntax; check manual corresponds mysql server version right syntax use near ''day', items.days, items.created_on) <= '2015-07-12 ' @ line 3"

i not think interval there, not able coerce db-specific date[time] functions. should use platform specific date[time] functions solve this.

if using postgresql, code below should work (assuming items.days integer):

q = (session.query(item)      .filter(func.age(now, item.created_on) <=              func.make_interval(0, 0, 0, item.days)              )      ) 

see postgres' date/time functions , operators more information.