I'd go with form validation -- you shouldn't allow a Purchase to be added to a transaction if a Purchase with a conflicting status is already in there, nor should a Purchase be able to be modified if it's in a transaction with another Purchase.
Then you never have to check whether a transaction is valid. The models pasted don't give the complete picture of the relationship, but garbage in, garbage out, so just don't allow them to exist in the first place. -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/django-users. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/CAOzwKwEOBTjZmAwwK_a7jTD1jyW0%2BVmeuSEVgdcQCNG7ts37Rw%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
