how to return a recordId in a subquery

[mrpanam]

i have the below query :

CREATE trade SET 
    qty = 200, 
    price = 75.00, 
    category = Category:Equity, 
    user = user:2, 
    portfolio = (SELECT id FROM portfolio WHERE name = 'FRA1' LIMIT 1), 
    event = event:rerate, 
    date = time::now() - 2w;

error msg :
'Found [{ id: portfolio:dfnxaj017ytptatg8cip }] for field portfolio, with record trade:9ee8wpi5twm4cutdjj7i,
but expected a record'portfolio'

how to return the record itself ?? didn't find in the documentation