I can't say I've ever really tried this, but maybe you could do something
like this in your model:
db.pineapple_insert(**kwargs):
if db(db.pineapple.id > 0).count() >= 3:
raise Exception('There are already 3 pineapples in this table.')
else:
db.pineapple.insert(**kwargs)
Then instead of calling db.pineapple.insert() in your controllers, you would
call db.pineapple_insert() <--- Notice the underscore instead of the dot.
This function is just a wrapper around DAL's insert() method, but does the
checking before actually calling the insert() method.
