order_by on the basis of time difference (updated_at - created_at)

[Aadil Rashid]

class ExampleModel(models.Model):

is_active = models.BooleanField(default=True)

created_at = models.DateTimeField(auto_now_add=True)

updated_at = models.DateTimeField(auto_now=True)

I want to query on UserModel such that the Query set which I get should be orderable in terms of time difference of updated_at - created_at,

I tried

ExampleModel.objects.all().order_by('updated_at' - 'created_at')
but this is not working
it throws, TypeError: unsupported operand type(s) for -: 'str' and 'str'

Django Family Please Help...................

[Lalit Suthar]

won't be possible like this, It will be easy if you have another entry in models which stores the difference between updated and created.

You can update that field whenever an object is updated. And then can run order_by on that field directly

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[Aadil Rashid]

This is nice idea, but I can't change the model, as discussed by teammates, i need to figure out any other way to do it on the go.

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[Feroz Ahmed]

Hi,

in VIEWS

def example=(request):

       fm=ExampleModel.object.created_at

     ExMd=ExampleModel.objects.filter(created_at__lt={'fm'})... ordering conditions.....

[Gabriel Araya Garcia]

Try this:

ExampleModel.objects.all().order_by('updated_at' , '-created_at')

Gabriel Araya Garcia

GMI - Desarrollo de Sistemas Informáticos

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[Fabio C. Barrionuevo da Luz]

this can be easily solved by using an annotation to calculate the difference and store it in a new temporary column, and then sort by it

from django.db.models import F
from myapp.models import ExampleModel

queryset = ExampleModel.objects.annotate(
    dt_difference=F('updated_at') - F('created_at')
).order_by('dt_difference')

for example in queryset[:10]:
    print(f'created_at={example.created_at} - updated_at={example.updated_at} - dt_difference={example.dt_difference}')

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--

Fábio C. Barrionuevo da Luz
Palmas - Tocantins - Brasil - América do Sul

http://pythonclub.com.br/

Blog colaborativo sobre Python e tecnologias Relacionadas, mantido totalmente no https://github.com/pythonclub/pythonclub.github.io .

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[Lalit Suthar]

Fabio C. Barrionuevo da Luz's answer will work like a charm!

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[DJANGO DEVELOPER]

you can use datetime.datetime.strptime to avoid this error. I resolved it few days back.

for this you have to import datetime like this: import datetime

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[Aadil Rashid]

Thank you very much Django family for your positive response, and especially to @Fabio C. Barrionuevo da Luz, 

Adding another field to the QuerySet using the "annotate"  function really helped and solves the problem like a charm! as side by @Lalit Suthar

Thank you once again everyone for sharing valuable information here; 

I learned a lot from your sujjections.

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