django - sort objects - need some help in logic

Question

I have Topiccenter Model:

class TopicCenter(models.Model):
  title = models.TextField()      
  def latest_entry(self):
    latest_entries = []
    book = self.tc_books.order_by('-id')[:1]
    journal = self.tc_journals.order_by('-id')[:1]
    if book: 
        for b in book:
            if b:
                latest_entries.append(b)
    if journal: 
        for jn in journal: 
            if jn: 
                latest_entries.append(jn)
    lastone = []
    if latest_entry:            
        lastone = max(latest_entries, key = lambda x: x.added)
    return lastone
    # what to return here if lastone is empty list ?? :(

each topiccenter can have many books and journals. I want to get the latest entry by its added field.

I am sorting now topiccenters by the date of its latest entry. Now the Problem i am facing is, some topiccenters are totally empty (no book, no journals) so i dont know what to return in latest_entry() method if latest_entry is [] so that I can use it here like this:

tcss = TopicCenter.objects.all().distinct('id')  
sorter = lambda x: x.latest_entry().added
tcs = sorted(tcss, key=sorter, reverse=True)

at this moment i am getting 'list' object has no attribute 'added' because one Topiccenter has neither book nor journal, so latest_entry() is returning [] which causing the error message.

can someone please help me how to solve this logic :(

@haki but i need to show also topics which dont have any entry with entry=0 — doniyor
– doniyor, Commented Jun 10, 2014 at 14:04
Then you need to decide the way as those empty-entry topics to be placed in the sorted result. — okm
– okm, Commented Jun 10, 2014 at 14:34

pcoronel · Accepted Answer · 2014-06-10 15:18:10Z

1

I assume you are using latest_entry() in other places too, so just create another method latest_added_time() which returns latest_entry.added or a fake time.

class TopicCenter(models.Model):
    ...
    def latest_added_time(self):
        latest = self.latest_entry()
        if latest:
            return latest.added
        else:
            # returns a time to place it at the end of the sorted list
            return datetime(1, 1, 1)

Then, you can just sort on this new method:

tcss = TopicCenter.objects.all().distinct('id')  
sorter = lambda x: x.latest_added_time()
tcs = sorted(tcss, key=sorter, reverse=True)

If you aren't using latest_entry() for anything else, then you should just put this logic directly into that function.

answered Jun 10, 2014 at 15:18

pcoronel

4,00124 silver badges25 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

S.Ali · Accepted Answer · 2014-06-10 13:25:53Z

0

You can try by changing your conditions

if not book and not journal:
    #Action you want to perform

or you can see if lastone list is empty you can append any message there like

if not len(lastone):
    #Your code to append a message

answered Jun 10, 2014 at 13:25

S.Ali

6922 gold badges5 silver badges14 bronze badges

1 Comment

doniyor Over a year ago

Thanks but this is not what i ask here. It should be sorted properly with what i am returning if there is no entry.

Collectives™ on Stack Overflow

django - sort objects - need some help in logic

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related