CODEWITHSUNDEEP
djangodjango-modelsdjango-orm
Brian M. Hunt
Brian M. Hunt

Reputation: 83858

Django ORM: Get most recent prior object that meets a certain condition

Given an object like:

class M(models.Model):
  test = models.BooleanField()
  created_date = models.DateTimeField(auto_now_add=True)

Given sample data (assume monotonically increasing automatic created_date):

M(test=False).save()

M(test=True).save()

M(test=False).save()

X = M(test=True).save()

M(test=False).save()

Y = M(test=False).save()

M(test=False).save()

M(test=True).save()

Can one use the Django ORM to create a query that would return X (the previous query, by date, where 'test'=True), if you are given Y? If so, how?

In other words: Given Y, how does one get the most recent previous element where 'test' is True?

Thoughts & feedback is appreciated, thanks!

Upvotes: 1

Views: 1625

Answers (2)

Baishampayan Ghose
Baishampayan Ghose

Reputation: 20696

Try this

M.objects.filter(created_date__lte=Y.created_date).filter(test=True)[0:1]

You can also add an order_by clause like

M.objects.filter(created_date__lte=Y.created_date)\
         .filter(test=True)\
         .order_by('-created_date')[0:1]

This should work.

Upvotes: 5

ayaz
ayaz

Reputation: 10510

With the help of Django field lookups, you may be able to achieve something to the effect of what you want with the following expression:

M.objects.filter( test=True, created_date__lt=Y.created_date ).order_by( '-created_date' )

Depending on whether there are or are not any elements in the resulting queryset object, you may pick up the very first one which will be the most recent object that you want.

Upvotes: 3

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