Search for a command to run...
How to do union of two querysets from same or different models?
Experienced Full Stack Software Engineer with 4+ Years of experience, proficient in Django and React, with expertise in Python, JavaScript and Typescript, also an author of Dev.Junction Blogs & YouTube Channel, expert in Python/Django, Rest Framework, ReactJS/NextJS and TypeScript, currently based in Pune, India.
No comments yet. Be the first to comment.
TypeScript, a Syntactic sugar on top of JavaScript
Are you tired of tightly coupled code and struggling to keep track of events in your Django application? Look no further! Our new e-book, "Django Signals Demystified: A Step-by-Step Guide to Event-Driven Programming" is here to help you master the po...
Maximizing Performance with select_related and prefetch_related in Django
2022 was not a good year financially because I did so many mistakes knowingly or unknowingly that, eventually, made me lose INR 500K over the course of just 6 months. So here are those mistakes which taught me about freelancing, finance management et...
Improve the user experience and efficiency of your React app with these simple techniques.
Assume you got two querysets from one or more models, and you want the querysets to combine into one, for that Django ORM provides a union method to combine those querysets.
The querysets can be from the same or from different models, just one thing to note here is that when the querysets are from different models, the fields and their data types must match.
Let’s have a look at this example of combing two querysets of same User model:
qs1 = User.objects.filter(id__gte=3)
# <QuerySet [<User: Ritesh>, <User: Billy>, <User: Radha>, <User: sohan>, <User: Raghu>, <User: rishab>]>
qs2 = User.objects.filter(id__lte=6)
# <QuerySet [<User: John>, <User: Ricky>, <User: Ritesh>, <User: Billy>, <User: Radha>, <User: sohan>]>
qs = qs1.union(qs2)
# <QuerySet [<User: John>, <User: Ricky>, <User: Ritesh>, <User: Billy>, <User: Radha>, <User: sohan>, <User: Raghu>, <User: rishab>]>
# We can also switch the places of qs1 and qs2 the results will be same
qs = qs2.union(qs1)
# <QuerySet [<User: John>, <User: Ricky>, <User: Ritesh>, <User: Billy>, <User: Radha>, <User: sohan>, <User: Raghu>, <User: rishab>]>
Let's understand how can we combine two querysets from two or more difference models: (But before that, keep in mind, when the querysets are from different models, the fields and their data types must match.)
qs1 = Author.objects.values_list('name')
qs2 = Entry.objects.values_list('headline')
qs = qs1.union(qs2)
# django.db.utils.OperationalError: SELECTs to the left and right of UNION do not have the same number of result columns
As you can see above that we got a OperationalError while performing the union of two querysets from different models.
Let’s check out, when we can union two queryetes of different models:
qs1 = Hero.objects.all().values_list("name", "gender")
qs2 = Villain.objects.all().values_list("name", "gender")
qs = qs1.union(qs2)
Above code will print the correct output without any errors, as we are performing the union based on two columns 'name' and 'gender' and both have same data types.
Any thoughts? Write it down in the comments.
For more such crispy blogs daily, follow Dev.Junction, subscribe to our newsletter and get notified.