Python/Peewee query with fn.MAX and alias results in "no such attribute"

Question

I have a peewee query that looks like this:

toptx24h = Transaction.select(fn.MAX(Transaction.amount).alias('amount'), User.user_name).join(User,on=(User.wallet_address==Transaction.source_address)).where(Transaction.created > past_dt).limit(1)

My understanding is this should be equivalent to:

select MAX(t.amount) as amount, u.user_name from transaction t inner join user u on u.wallet_address = t.source_address where transaction.created > past_dt limit 1

My question is how to I access the results user_name and amount

When I try this, I get an error saying top has no attribute named amount

for top in toptx24h:
    top.amount # No such attribute amount

I'm just wondering how i can access the amount and user_name from the select query.

Thanks

Answer 1

I think you need a GROUP BY clause to ensure you're grouping by User.username.

I wrote some test code and confirmed it's working:

    with self.database.atomic():
        charlie = TUser.create(username='charlie')
        huey = TUser.create(username='huey')

        data = (
            (charlie, 10.),
            (charlie, 20.),
            (charlie, 30.),
            (huey, 1.5),
            (huey, 2.5))
        for user, amount in data:
            Transaction.create(user=user, amount=amount)

    amount = fn.MAX(Transaction.amount).alias('amount')
    query = (Transaction
             .select(amount, TUser.username)
             .join(TUser)
             .group_by(TUser.username)
             .order_by(TUser.username))
    with self.assertQueryCount(1):
        data = [(txn.amount, txn.user.username) for txn in query]

    self.assertEqual(data, [
        (30., 'charlie'),
        (2.5, 'huey')])