CODEWITHSUNDEEP
pythondjangodjango-modelsdjango-queryset
Didi
Didi

Reputation: 11

Django method same object not saving

This is something I have been trying to solve for 3 days now and I just can't get my head around it why this is not working.

I have a method that creates a new version of an Object. It used to work, that you would pass in the sou obj. and this would be the source from which a new version is created. You can also pass in a destination, which is not really important in this example. Now I wanted to add locking to this method as we want to add multiple users. So I want to be sure that I always have the most current object from which I create a new one. So I added a line that would just get the newest object. If there is no newer object in the database it would be the same anyway.

def createRevision(request, what, sou, destination=None, ignore = [], **args):
...
  if "initial" not in args.keys():
    source = get_object_or_404(BaseItem, ppk=sou.ppk, project=sou.project, current=True)
    print "------------"
    print source == sou
    print "------------"
    # This outputs True
  else:
    source = sou

further down in the method I do something like

source.current = False
source.save()

Basically the idea is that I pass in BaseItem and if I don't specify the "initial" keyword then I get the current item from that project with the same ppk (Which is a special random pk in conduction with current). I do this just to be on the save side, that I really have the most current object. And if it is the initial version I just use that one, as there can not be another version.

So now the problem is, that everything works fine if I use sou in this method. I can save it etc .. but as soon as I use source and initial is not in the args it just doesn't save it. The print statement tells me they are the same. Everything I print after the save tells me it has been saved but it just doesn't do it.

source.current = False
source.save()
print "SAVED !!!!"
print source.pk
print source.current
rofl =  get_object_or_404(BaseItem, pk=source.pk, project=sou.project)
print rofl.pk
print source.current

outputs the same pk and the same current value but somehow it is not properly saved. As soon as I look into django admin or do a select current = True.

I really don't know what to do anymore.

Why does it work without a problem if I pass in the object into the method but starts to fail when I get the exact same object in the method?

Of course I call the method with the same object:

x = get_object_or_404(BaseItem, ppk=sou.ppk, project=sou.project, current=True)
createRevision(request, "", x)

Upvotes: 0

Views: 353

Answers (2)

Didi
Didi

Reputation: 11

Thank you pztrick for the hint with the caches. I finally solved it. So the problem was that I was doing:

x = get_object_or_404(BaseItem, ppk=sou.ppk, project=sou.project, current=True)
createRevision(request, "", x)
# .... loads of lines of code
unlock(x)

unlock is a method I wrote that just sets a timestamp so I know no other user is editing it. So now the problem was that I was saving x in createRevision with all the correct data but of course unlock(x) still had a reference to an "old" not updated object and of course was saving it again. Hence it was overwriting my changes in createRevision.

Thank you again to everyone who helped with this.

Upvotes: 1

pztrick
pztrick

Reputation: 3831

I think you may be running afoul of model manager caching which is intended to limit database queries. However, by invoking the .all() method on the model manager you force it to hit the databse again.

So, try this: Replace your argument from the BaseItem class to the model manager's .all() QuerySet:

source = get_object_or_404(BaseItem.objects.all(), ppk=sou.ppk, project=sou.project, current=True)
# ...
rofl =  get_object_or_404(BaseItem.objects.all(), pk=source.pk, project=sou.project)

get_object_or_404 supports mode classes, model managers, or QuerySets as the first parameter so this is valid.

Upvotes: 0

Related Questions