Django QuerySet date manipulation












0















I have a model storing, among other things, a timezone datetime object. I am reaching out with an Ajax call from the website to one of my views, which does the following call:



def uploads(request):

user = User.objects.get(username=request.user.get_username())
cases = Case.objects.filter(user_id=user.pk).order_by('-uploaded_on')[:5]

return JsonResponse(serializers.serialize('json', cases, fields=('col1', 'col2', 'col3', 'uploaded_on')), safe=False)


When a JSON response is received at the Front End, it gets parsed with JS and analyzed. What I would like to do here, is to modify the 'uploaded_on' column with user's timezone (which I can already access with user.timezone, currently displayed as a string e.g. 'Germany/Berlin', but can easily convert it to a necessary object with e.g. pytz package).



When I try to iterate through the QuerySet like below, the values received on the Front End do not change:



for case in cases:
case.uploaded_on.astimezone(pytz.timezone(user.timezone))


This is probably related to the fact that QuerySets are lazy, like described in Django's documentation. Can anyone suggest how this can be done?



A bonus question as well: with Django's serializer, can I pass along more than one QuerySet in a single JSON response? When I try to pack a few in a list, I get a MultiValueDictKeyError:



return JsonResponse(serializers.serialize('json', [cases, cases2]), safe=False)









share|improve this question



























    0















    I have a model storing, among other things, a timezone datetime object. I am reaching out with an Ajax call from the website to one of my views, which does the following call:



    def uploads(request):

    user = User.objects.get(username=request.user.get_username())
    cases = Case.objects.filter(user_id=user.pk).order_by('-uploaded_on')[:5]

    return JsonResponse(serializers.serialize('json', cases, fields=('col1', 'col2', 'col3', 'uploaded_on')), safe=False)


    When a JSON response is received at the Front End, it gets parsed with JS and analyzed. What I would like to do here, is to modify the 'uploaded_on' column with user's timezone (which I can already access with user.timezone, currently displayed as a string e.g. 'Germany/Berlin', but can easily convert it to a necessary object with e.g. pytz package).



    When I try to iterate through the QuerySet like below, the values received on the Front End do not change:



    for case in cases:
    case.uploaded_on.astimezone(pytz.timezone(user.timezone))


    This is probably related to the fact that QuerySets are lazy, like described in Django's documentation. Can anyone suggest how this can be done?



    A bonus question as well: with Django's serializer, can I pass along more than one QuerySet in a single JSON response? When I try to pack a few in a list, I get a MultiValueDictKeyError:



    return JsonResponse(serializers.serialize('json', [cases, cases2]), safe=False)









    share|improve this question

























      0












      0








      0








      I have a model storing, among other things, a timezone datetime object. I am reaching out with an Ajax call from the website to one of my views, which does the following call:



      def uploads(request):

      user = User.objects.get(username=request.user.get_username())
      cases = Case.objects.filter(user_id=user.pk).order_by('-uploaded_on')[:5]

      return JsonResponse(serializers.serialize('json', cases, fields=('col1', 'col2', 'col3', 'uploaded_on')), safe=False)


      When a JSON response is received at the Front End, it gets parsed with JS and analyzed. What I would like to do here, is to modify the 'uploaded_on' column with user's timezone (which I can already access with user.timezone, currently displayed as a string e.g. 'Germany/Berlin', but can easily convert it to a necessary object with e.g. pytz package).



      When I try to iterate through the QuerySet like below, the values received on the Front End do not change:



      for case in cases:
      case.uploaded_on.astimezone(pytz.timezone(user.timezone))


      This is probably related to the fact that QuerySets are lazy, like described in Django's documentation. Can anyone suggest how this can be done?



      A bonus question as well: with Django's serializer, can I pass along more than one QuerySet in a single JSON response? When I try to pack a few in a list, I get a MultiValueDictKeyError:



      return JsonResponse(serializers.serialize('json', [cases, cases2]), safe=False)









      share|improve this question














      I have a model storing, among other things, a timezone datetime object. I am reaching out with an Ajax call from the website to one of my views, which does the following call:



      def uploads(request):

      user = User.objects.get(username=request.user.get_username())
      cases = Case.objects.filter(user_id=user.pk).order_by('-uploaded_on')[:5]

      return JsonResponse(serializers.serialize('json', cases, fields=('col1', 'col2', 'col3', 'uploaded_on')), safe=False)


      When a JSON response is received at the Front End, it gets parsed with JS and analyzed. What I would like to do here, is to modify the 'uploaded_on' column with user's timezone (which I can already access with user.timezone, currently displayed as a string e.g. 'Germany/Berlin', but can easily convert it to a necessary object with e.g. pytz package).



      When I try to iterate through the QuerySet like below, the values received on the Front End do not change:



      for case in cases:
      case.uploaded_on.astimezone(pytz.timezone(user.timezone))


      This is probably related to the fact that QuerySets are lazy, like described in Django's documentation. Can anyone suggest how this can be done?



      A bonus question as well: with Django's serializer, can I pass along more than one QuerySet in a single JSON response? When I try to pack a few in a list, I get a MultiValueDictKeyError:



      return JsonResponse(serializers.serialize('json', [cases, cases2]), safe=False)






      python json django timezone






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      asked Nov 13 '18 at 23:14









      Greem666Greem666

      9810




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          2 Answers
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          To me there would be two approaches:





          1. Annotate the cases queryset with a new column, something like uploaded_at_utz and do timezone manipulation at database level. For example you could use TruncSecond function to do something like the following:



            cases = Case.objects.filter(user_id=user.pk).annotate(uploaded_at_utz=TruncSecond('uploaded_on', tzinfo=pytz.timezone(user.timezone)).order_by('-uploaded_on')[:5]



          2. The other approach would be to do this at python level. For this I would go for a generator function, something like:



            def convert_to_timezone(cases, tzinfo):
            for case in cases:
            case.uploaded_on = case.uploaded_on.astimezone(tzinfo)
            yield case



          Then, in you would pass convert_to_timezone(cases, pytz.timezone(user.timezone)) to your JsonResponse constructor.



          You should also explore the use of timezone.override and/or timezone.localtime although I'm not familiar with them.






          share|improve this answer































            0














            Regarding the date manipulation, datetime.astimezone() returns a new datetime rather than converting in-place. You'd need to assign the converted value back to case.uploaded_on.



            for case in cases:
            case.uploaded_on = case.uploaded_on.astimezone(pytz.timezone(user.timezone))


            Regarding whether you can pass along more than one queryset in a single JSON response, you can use itertools.chain to do that.



            from itertools import chain

            return JsonResponse(serializers.serialize('json', chain(cases, cases2)), safe=False)





            share|improve this answer























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              2 Answers
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              2 Answers
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              0














              To me there would be two approaches:





              1. Annotate the cases queryset with a new column, something like uploaded_at_utz and do timezone manipulation at database level. For example you could use TruncSecond function to do something like the following:



                cases = Case.objects.filter(user_id=user.pk).annotate(uploaded_at_utz=TruncSecond('uploaded_on', tzinfo=pytz.timezone(user.timezone)).order_by('-uploaded_on')[:5]



              2. The other approach would be to do this at python level. For this I would go for a generator function, something like:



                def convert_to_timezone(cases, tzinfo):
                for case in cases:
                case.uploaded_on = case.uploaded_on.astimezone(tzinfo)
                yield case



              Then, in you would pass convert_to_timezone(cases, pytz.timezone(user.timezone)) to your JsonResponse constructor.



              You should also explore the use of timezone.override and/or timezone.localtime although I'm not familiar with them.






              share|improve this answer




























                0














                To me there would be two approaches:





                1. Annotate the cases queryset with a new column, something like uploaded_at_utz and do timezone manipulation at database level. For example you could use TruncSecond function to do something like the following:



                  cases = Case.objects.filter(user_id=user.pk).annotate(uploaded_at_utz=TruncSecond('uploaded_on', tzinfo=pytz.timezone(user.timezone)).order_by('-uploaded_on')[:5]



                2. The other approach would be to do this at python level. For this I would go for a generator function, something like:



                  def convert_to_timezone(cases, tzinfo):
                  for case in cases:
                  case.uploaded_on = case.uploaded_on.astimezone(tzinfo)
                  yield case



                Then, in you would pass convert_to_timezone(cases, pytz.timezone(user.timezone)) to your JsonResponse constructor.



                You should also explore the use of timezone.override and/or timezone.localtime although I'm not familiar with them.






                share|improve this answer


























                  0












                  0








                  0







                  To me there would be two approaches:





                  1. Annotate the cases queryset with a new column, something like uploaded_at_utz and do timezone manipulation at database level. For example you could use TruncSecond function to do something like the following:



                    cases = Case.objects.filter(user_id=user.pk).annotate(uploaded_at_utz=TruncSecond('uploaded_on', tzinfo=pytz.timezone(user.timezone)).order_by('-uploaded_on')[:5]



                  2. The other approach would be to do this at python level. For this I would go for a generator function, something like:



                    def convert_to_timezone(cases, tzinfo):
                    for case in cases:
                    case.uploaded_on = case.uploaded_on.astimezone(tzinfo)
                    yield case



                  Then, in you would pass convert_to_timezone(cases, pytz.timezone(user.timezone)) to your JsonResponse constructor.



                  You should also explore the use of timezone.override and/or timezone.localtime although I'm not familiar with them.






                  share|improve this answer













                  To me there would be two approaches:





                  1. Annotate the cases queryset with a new column, something like uploaded_at_utz and do timezone manipulation at database level. For example you could use TruncSecond function to do something like the following:



                    cases = Case.objects.filter(user_id=user.pk).annotate(uploaded_at_utz=TruncSecond('uploaded_on', tzinfo=pytz.timezone(user.timezone)).order_by('-uploaded_on')[:5]



                  2. The other approach would be to do this at python level. For this I would go for a generator function, something like:



                    def convert_to_timezone(cases, tzinfo):
                    for case in cases:
                    case.uploaded_on = case.uploaded_on.astimezone(tzinfo)
                    yield case



                  Then, in you would pass convert_to_timezone(cases, pytz.timezone(user.timezone)) to your JsonResponse constructor.



                  You should also explore the use of timezone.override and/or timezone.localtime although I'm not familiar with them.







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered Nov 14 '18 at 0:24









                  ivissaniivissani

                  57146




                  57146

























                      0














                      Regarding the date manipulation, datetime.astimezone() returns a new datetime rather than converting in-place. You'd need to assign the converted value back to case.uploaded_on.



                      for case in cases:
                      case.uploaded_on = case.uploaded_on.astimezone(pytz.timezone(user.timezone))


                      Regarding whether you can pass along more than one queryset in a single JSON response, you can use itertools.chain to do that.



                      from itertools import chain

                      return JsonResponse(serializers.serialize('json', chain(cases, cases2)), safe=False)





                      share|improve this answer




























                        0














                        Regarding the date manipulation, datetime.astimezone() returns a new datetime rather than converting in-place. You'd need to assign the converted value back to case.uploaded_on.



                        for case in cases:
                        case.uploaded_on = case.uploaded_on.astimezone(pytz.timezone(user.timezone))


                        Regarding whether you can pass along more than one queryset in a single JSON response, you can use itertools.chain to do that.



                        from itertools import chain

                        return JsonResponse(serializers.serialize('json', chain(cases, cases2)), safe=False)





                        share|improve this answer


























                          0












                          0








                          0







                          Regarding the date manipulation, datetime.astimezone() returns a new datetime rather than converting in-place. You'd need to assign the converted value back to case.uploaded_on.



                          for case in cases:
                          case.uploaded_on = case.uploaded_on.astimezone(pytz.timezone(user.timezone))


                          Regarding whether you can pass along more than one queryset in a single JSON response, you can use itertools.chain to do that.



                          from itertools import chain

                          return JsonResponse(serializers.serialize('json', chain(cases, cases2)), safe=False)





                          share|improve this answer













                          Regarding the date manipulation, datetime.astimezone() returns a new datetime rather than converting in-place. You'd need to assign the converted value back to case.uploaded_on.



                          for case in cases:
                          case.uploaded_on = case.uploaded_on.astimezone(pytz.timezone(user.timezone))


                          Regarding whether you can pass along more than one queryset in a single JSON response, you can use itertools.chain to do that.



                          from itertools import chain

                          return JsonResponse(serializers.serialize('json', chain(cases, cases2)), safe=False)






                          share|improve this answer












                          share|improve this answer



                          share|improve this answer










                          answered Nov 14 '18 at 13:25









                          Will KeelingWill Keeling

                          11.6k22434




                          11.6k22434






























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