How to create a Django queryset filter comparing two date fields in the same model

djangodjango-queryset

Trying to get a query where the Activity record is stale in my Solr Index.
I want to check to see if the Activity.updated date in the database is greater than the Activity.added_toSolr_date for the same record.

stale_activities_queryset = Activity.objects.filter(updated__gte = self.added_toSolr_date)

Model

class Activity(models.Model):
    # Last time entry / metric was updated in the Activity model database
    updated =  models.DateTimeField( verbose_name="CRUD date")
    # When it was added to Solr Index Date
    added_toSolr_date = models.DateTimeField(blank=True, null=True, verbose_name="Added to Solr Index Date")

I referenced Django Query docs:
https://docs.djangoproject.com/en/1.4/ref/models/querysets/
And unit tests for samples:
https://github.com/django/django/blob/master/tests/modeltests/or_lookups/tests.py

Also searched here on Stackoverflow. All the examples use an entered date instead of comparing two date fields in the same model.

Best Answer

F objects.

from django.db.models import F
stale_activities = Activity.objects.filter(updated__gte=F('added_toSolr_date'))

Related Solutions

Extending the User model with custom fields in Django

The least painful and indeed Django-recommended way of doing this is through a OneToOneField(User) property.

Extending the existing User model

…

If you wish to store information related to User, you can use a one-to-one relationship to a model containing the fields for additional information. This one-to-one model is often called a profile model, as it might store non-auth related information about a site user.

That said, extending django.contrib.auth.models.User and supplanting it also works...

Substituting a custom User model

Some kinds of projects may have authentication requirements for which Django’s built-in User model is not always appropriate. For instance, on some sites it makes more sense to use an email address as your identification token instead of a username.

[Ed: Two warnings and a notification follow, mentioning that this is pretty drastic.]

I would definitely stay away from changing the actual User class in your Django source tree and/or copying and altering the auth module.

How to combine two or more querysets in a Django view

Concatenating the querysets into a list is the simplest approach. If the database will be hit for all querysets anyway (e.g. because the result needs to be sorted), this won't add further cost.

from itertools import chain
result_list = list(chain(page_list, article_list, post_list))

Using itertools.chain is faster than looping each list and appending elements one by one, since itertools is implemented in C. It also consumes less memory than converting each queryset into a list before concatenating.

Now it's possible to sort the resulting list e.g. by date (as requested in hasen j's comment to another answer). The sorted() function conveniently accepts a generator and returns a list:

result_list = sorted(
    chain(page_list, article_list, post_list),
    key=lambda instance: instance.date_created)

If you're using Python 2.4 or later, you can use attrgetter instead of a lambda. I remember reading about it being faster, but I didn't see a noticeable speed difference for a million item list.

from operator import attrgetter
result_list = sorted(
    chain(page_list, article_list, post_list),
    key=attrgetter('date_created'))

Best Answer

F objects.

Related Solutions

Extending the User model with custom fields in Django

Extending the existing User model

Substituting a custom User model

How to combine two or more querysets in a Django view

Related Topic