simple way for QuerySet union and subtraction in django?

Question

Consider two QuerySet objects of the same class. Is there a simple way to unify them into a single QuerySet by calculating the union? Also, is there a simple way to subtract them? Removing all elements that appear in both sets from one of the sets?

Answer 1

Since Django 1.11, QuerySets have union(), intersection() and difference() methods.

It's also possible to use & and | operators with QuerySets (I could not find a reference to this in the docs, so I guess union() and intersection() is the preferred way to combine two querysets.

qs3 = qs1.union(qs2)         # or qs3 = qs1 | qs2 qs3 = qs1.intersection(qs2)  # or qs3 = qs1 & qs2 qs3 = qs1.difference(qs2)    # the ^ operator is not implemented. 

You can also use Q() objects which like QuerySets implement | and &, and additionally the inversion operator ~

Answer 2

Subtract a QuerySet from another QuerySet using the same model.

This works - but is probably slowly

queryset_with_hello = Blog.objects.filter(name__icontains='hello') queryset_without_hello = Blog.objects.exclude(pk__in=queryset_with_hello) 

Read the performance considerations in django documentation:

https://docs.djangoproject.com/en/dev/ref/models/querysets/#in