CODEWITHSUNDEEP
pythondjango
raj-kapil
raj-kapil

Reputation: 447

How to traverse over reversed queryset in django?

I am trying to traverse twice over one reversed object, initally the for loop works but not on the second loop.

x = Subscription.objects.filter(customer_id=customer_id).order_by('-id')[:count]
tmp = reversed(x)
y = call_function(subs=tmp) # inside this function as well object is of type reversed and i am able to loop over it inside the call_function.

for j in tmp: # this loop is not running at all. here as well tmp is a reversed object
    print(j)

# call_function(subs=s)
def call_function(s):
    for i in s:
       print(i)

Upvotes: 1

Views: 253

Answers (1)

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 477160

reversed(…) [Python-doc] is an iterator, not an iterable, so the second time you loop, the iterator is already "exhausted". It is thus just a "shallow object", that "walks" through the QuerySet in reversed order.

You thus use reversed(…) twice. This will not make the query a second time, since the QuerySet will cache the result, so:

x = Subscription.objects.filter(customer_id=customer_id).order_by('-id')[:count]
tmp = reversed(x)
y = call_function(subs=tmp)

for j in reversed(x):
    print(j)

Upvotes: 1

Related Questions