While update()ing fields are translated to column names, so you don't have
to fetch the record just to increment it.
>>>db.define_table('myupdates', Field('quantity', 'integer'))
>>>db(db.myupdates.id == 1)._update(quantity=db.myupdates.quantity + 1)
'UPDATE myupda SET quantity=(myupda.quantity + 1) WHERE (myupda.id = 1);'
That piece of code (updating the product) is correct.
On Saturday, February 23, 2013 5:22:04 PM UTC+1, Anthony wrote:
>
> db(db.product.id==key).update(quantity=db.product.quantity -
>> value)
>
>
> Here you probably want:
>
> db(db.product.id==key).update(quantity=db.product(key).quantity -value
> )
>
> db.product.quantity is a Field object, but you want to get the value of
> that field for the particular record, which is db.product(key).quantity.
>
> Anthony
>
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