trouble with forms/CreateView

[clavie...@gmail.com]

I seem to be having trouble understanding some of how form validation works, resulting in two problems. 

I am trying to write a CreateView in which a user can type in an item number, and the program will use that instead of the item's primary key to perform the lookup. 

The docs appear to recommend overriding form_valid, but these are the issues I've been running into: 

1. I would need duplicate code in both form_valid and form_invalid because the item number entered by the user may or may not also happen to be a primary key for a different item. As far as I've seen, Django assumes that the input is a primary key, and will call either method as appropriate based on whether or not it could find an item with that primary key.
   
2. Overriding form_invalid doesn't seem to be working anyway:
   
• Django appears to clean data before validating it, and I believe cleaned data is immutable. 
• CreateView has no clean() method to override that I can find (either here or the source code itself on github)
• I made a ModelForm to use with CreateView expressly for the clean() methods it offers, but neither clean() nor clean_<field> are being called (my breakpoints are being skipped). 

Does anybody know a way to accomplish this? How does CreateView clean its data? Any suggestions would be helpful.

Thank you!

Heather