In this tutorial, I will explain to you how you can access the first or last object in the queryset object. I will also cover how you can resolve any indexing error you may come across while performing operations on queryset.
Let’s understand the background first.
Did you come across this error?
IndexError at /profile/ list index out of range Request Method: GET Request URL: http://127.0.0.1:8000/profile/ Django Version: 3.1.3 Exception Type: IndexError Exception Value: list index out of range Exception Location: /project/venv/lib/python3.6/site-packages/django/db/models/query.py, line 325, in __getitem__ Python Executable: /project/venv/bin/python Python Version: 3.6.9 Python Path:
In Python, an error “List index out of range” usually occurs when you try to access the element in the Python list by an index that is out of the actual list index range. This error also occurs when you try to access the first element in the empty list.
A similar error can occur in Django when the user tries to access the queryset object.
Suppose you want to access the first “MyModel” data entry for a specific user. This is how you can write a code for it.
MyModel.objects.filter(user=request.user).[0]
Here we are using Python index ‘0’ to access the first object in the queryset similar to how we access the first element in the list.
Now the problem is…
If there is no matching object, filter() the function returns an empty queryset and when you try to access the first element in the query set using the index, you will get “index Error: list index out of range”.
So,
To avoid this error, Django has introduced first() method.
It is always good practice to use the first() method instead of indexing ‘0’ on the queryset.
MyModel.objects.filter(user=request.user).first()
Now, even if there is no matching queryset object, it will not throw an error. Instead, in this case, it will return None.
Using first() method for accessing the first element in the queryset is standard practice. Similarly, you can use the last() method for accessing the last queryset object.
Related article: How to sort objects in the Django queryset?
There can many ways to solve the problem. You have to be very precise and careful choosing one. That’s the programming!
I am complete Python Nut, love Linux and vim as an editor. I hold a Master of Computer Science from NIT Trichy. I dabble in C/C++, Java too. I keep sharing my coding knowledge and my own experience on <b>CSEstack.org</b> portal.
