Django - How to remove F() from a field?

Question

Hello guys, after doing a query with F() (see http://docs.djangoproject.com/en/dev/topics/db/queries/#query-expressions), I save the object, but then, I need to save it again. I want to remove F() from the field. If I don't, F() gets called again.

For example

rank.ammountMatchesRanked = F('ammountMatchesRanked') + 1
rank.save() # does ammountMatchesRanked = ammountMatchesRanked + 1
... # Manipulating more rank fields (can't manipulate before)
rank.save() # does ammountMatchesRanked++ again (undesired)

Any idea on how can I clear reference fields? I have searched the documentation but I didn't find it.

Thanks in advance

Answer 1

i am not that good in django, but what about doing this:

rank.ammountMatchesRanked = F('ammountMatchesRanked');

just before the second call?

Answer 2

Why are you using F() here at all? F is really for use within queries, where you want to just get those objects who have a certain property with some relation to another property in the same model. Once you've got the object, there's no need to use it - you can just do it in standard Python:

rank.ammountMatchesRanked += 1
rank.save()

Edited after comment No, you have misunderstood what lazy loading is. It applies to instances (ie database rows) within a queryset, not fields (ie columns) within an instance. So once you have accessed an instance at all, Django by default will load all its fields (except those you have marked with defer()), so the above will not result in an extra query.

The documentation for using F() in updates which you linked to explains that this is only if you're not doing anything else with the object. You are, so this is not an optimisation.