Re: Combining querysets while maintaining desired ordering?

Hi Simon,

Thanks for the clarification of the operation of the .union() method - the operative phrase in the docs appears to be "combine the results of two or more QuerySets" - perfect!

My project is currently using 1.8 LTS - I can defer this until I roll forward to 1.11 LTS (hopefully sometime soon).

Thanks again,

R.

On Sat, Jun 3, 2017 at 6:31 PM, Simon Charette <charette.s@gmail.com> wrote:

Hello Richard,

Since Django 1.11 you should be able to use the QuerySet.union() method[0] for that.

queryset = self.many_field1.order_by('some', 'fields')

combined = queryset.union(self.many_field2.order_by('some', 'fields'))

Best,

Simon

[0] https://docs.djangoproject.com/en/1.11/ref/models/querysets/#union

Le samedi 3 juin 2017 20:20:11 UTC-4, Richard Brockie a écrit :

Hi,

I am combining querysets of the same model in the following manner:

class ExampleModel(models.Model):
    many_field1 = models.ManyToManyField('Model', related_name='name1')
    many_field2 = models.ManyToManyField('Model', related_name='name2')

    def combined_many_fields(self):
        qs1 = self.many_field1.all().order_by('some', 'fields')
        qs2 = self.many_field2.all().order_by('some', 'fields')

        return qs1 | qs2

The result of the above code is that the order_by() methods are applied after the querysets are combined. This means that the two querysets can intermingle. I want them to be sorted before combination, not after, and retain being a queryset.

There are ways to force the evaluation of the individual querysets first and return a combination in the preferred order.

    def combined_many_fields(self):

        from itertools import chain

       return chain(qs1, qs2)

However, this is no longer a queryset, and therefore cannot be operated on with subsequent queryset methods. Is there a way to apply the ordering first and retain the queryset nature of the combination?

Am I trying to do something that is outside the scope of a queryset?

--
You received this message because you are subscribed to a topic in the Google Groups "Django users" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/django-users/au1f0zHq64M/unsubscribe.
To unsubscribe from this group and all its topics, send an email to django-users+unsubscribe@googlegroups.com.
To post to this group, send email to django-users@googlegroups.com.
Visit this group at https://groups.google.com/group/django-users.
To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/5631ac9b-17a6-401d-9b2b-841440daf7f7%40googlegroups.com.

For more options, visit https://groups.google.com/d/optout.

--

    R.

Richard Brockie

Real-time bicycle race results - www.ontheday.net

--
You received this message because you are subscribed to the Google Groups "Django users" group.
To unsubscribe from this group and stop receiving emails from it, send an email to django-users+unsubscribe@googlegroups.com.
To post to this group, send email to django-users@googlegroups.com.
Visit this group at https://groups.google.com/group/django-users.
To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/CAKv-vOWukVt%2BbSByuZAxdX4PMSv%2Bh1EVbnEW0tHpCkj7ogBA3A%40mail.gmail.com.
For more options, visit https://groups.google.com/d/optout.