web2py check if exist in db insert or update

Question

I'm trying to perform a check to see if a record exist first before inserting the record so I won't get an error. If it exists, i'll update a field.

mydb(mydb.myitems.itemNumber==int(row)).update(oldImageName=fileName) or 
mydb.myitems.insert(itemNumber=int(row),oldImageName=fileName)

If i try to update a record that does not exist, then it should throw a 1 or something aside from 0. But in the case above, it always throws a 0 so the insert keeps happening.

Why is that?

Thanks!

UPDATE: Adding model:

mydb.define_table('myitems', 
                    Field('itemNumber', 'id',notnull=True,unique=True),
                    Field('oldImageName', 'string')

Answer 1

If i try to update a record that does not exist, then it should throw a 1 or something aside from 0.

If you try to update a record that does not exist, .update() will return None, so the insert will then happen. If matching records exist, .update() will return the number of records updated.

In any case, you should instead do:

mydb.myitems.update_or_insert(mydb.myitems.itemNumber == int(row),
                              oldImageName=filename)

or alternatively:

mydb.myitems.update_or_insert(dict(itemNumber == int(row)),
                              oldImageName=filename)

The first argument to update_or_insert is _key, which can either be a DAL query or a dictionary with field names as keys.

Answer 2

This is basically a correction of Anthony's answer which did not give quite the desired result when I tried it. If you do:

mydb.myitems.update_or_insert(mydb.myitems.itemNumber == int(row),
                          itemNumber = int(row),
                          oldImageName=filename)

then the code should insert a record with the itemNumber and filename if there is not an item with that number there already, otherwise update it.

If you miss the itemNumber = int(row), bit then web2py makes up an itemNumber which is probably not what is wanted.

See http://www.web2py.com/books/default/chapter/29/06/the-database-abstraction-layer#update_or_insert