Giacomo Sarrocco Giacomo Sarrocco - 2 months ago 26
Python Question

Distinct values with Q objects

I have this query on my Django project 1.10.1 on Py3:

Event.objects.filter(Q(subject=topic.id) | Q(object=topic.id) | Q(place=topic.id))


How can I prevent to get two identical
Event
records?

Thank you in advance.

Answer

Use the distinct operator:

Event.objects.filter(Q(subject=topic.id) | Q(object=topic.id) | Q(place=topic.id)).distinct()

From the documentation:

By default, a QuerySet will not eliminate duplicate rows. In practice, this is rarely a problem, because simple queries such as Blog.objects.all() don’t introduce the possibility of duplicate result rows. However, if your query spans multiple tables, it’s possible to get duplicate results when a QuerySet is evaluated. That’s when you’d use distinct().

Make special note of their "However" clause before implementing this unless you expect to actually see duplicate results.

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