Checking for empty queryset in Django

Question

What is the recommended idiom for checking whether a query returned any results  Example   orgs   Organisation objects filter name  iexact    Fjuk inc     If any results       Do this with the results without querying again    Else  do something else      I suppose there are several different ways of checking this  but I d like to know how an experienced Django user would do it  Most examples in the docs just ignore the case where nothing was found

User · Answer

If you have a huge number of objects  this can  at times  be much faster   try      orgs 0        If you get here  it exists    except IndexError        Doesn t exist    On a project I m working on with a huge database  not orgs is 400  ms and orgs count   is 250ms  In my most common use cases  those where there are results   this technique often gets that down to under 20ms   One case I found  it was 6    Could be much longer  of course  depending on how far the database has to look to find a result  Or even faster  if it finds one quickly  YMMV   EDIT  This will often be slower than orgs count   if the result isn t found  particularly if the condition you re filtering on is a rare one  as a result  it s particularly useful in view functions where you need to make sure the view exists or throw Http404   Where  one would hope  people are asking for URLs that exist more often than not

User · Answer

if not orgs        Do this    else        Do that

User · Answer

To check the emptiness of a queryset   if orgs exists          Do something   or you can check for a the first item in a queryset  if it doesn t exist it will return None   if orgs first          Do something

User · Answer

The most efficient way  before django 1 2  is this   if orgs count      0        no results else        alrigh  let s continue

User · Answer

You could also use this   if not orgs         if orgs is empty  else       if orgs is not empty

User · Answer

Since version 1 2  Django has QuerySet exists   method which is the most efficient   if orgs exists          Do this    else        Do that      But if you are going to evaluate QuerySet anyway it s better to use   if orgs           For more information read QuerySet exists   documentation

User · Answer

I disagree with the predicate  if not orgs    It should be   if not orgs count      I was having the same issue with a fairly large result set   150k results   The operator is not overloaded in QuerySet  so the result is actually unpacked as a list before the check is made  In my case execution time went down by three orders

[django] Checking for empty queryset in Django

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