Ordering and slicing querysets in Django - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this queryset slicing?

Given a Django model Book with 10 entries ordered by published_date, what does Book.objects.order_by('published_date')[2:5] return?

A A queryset with the 2nd, 3rd, and 4th books ordered by published_date

B A queryset with the last 3 books ordered by published_date

C A queryset with the 3rd, 4th, and 5th books ordered by published_date

D A queryset with the 1st, 2nd, and 3rd books ordered by published_date

💡 Hint

Remember Python slicing starts at index 0 and excludes the stop index.

The slice [2:5] selects items starting at index 2 up to but not including index 5. So it returns the 3rd, 4th, and 5th books in the ordered queryset.

📝 Syntax

intermediate

Which queryset ordering syntax is correct?

Select the correct way to order a queryset of Author by last name descending and then first name ascending.

A Author.objects.order_by('last_name', '-first_name')

B Author.objects.order_by('-last_name', 'first_name')

C Author.objects.order_by('last_name-', 'first_name')

D Author.objects.order_by('last_name desc', 'first_name asc')

💡 Hint

Use a minus sign before the field name for descending order.

In Django, prefixing a field name with - orders descending. So order_by('-last_name', 'first_name') orders by last name descending, then first name ascending.

🔧 Debug

advanced

Why does this queryset slicing cause an error?

Consider this code: books = Book.objects.order_by('title')[5:2]. What happens when this runs?

A Returns an empty queryset because the slice start is greater than stop

B Raises a SyntaxError due to invalid slice syntax

C Returns the last 3 books ordered by title

D Raises a ValueError because slicing with start > stop is not allowed

💡 Hint

Think about how Python slicing behaves when start index is larger than stop index.

Python slicing with start index greater than stop index returns an empty list or queryset. It does not raise an error.

🧠 Conceptual

advanced

How does chaining order_by calls affect the queryset?

What is the result of this queryset: Book.objects.order_by('author').order_by('published_date')?

A The queryset is ordered only by published_date, ignoring author

B The queryset is ordered by author and published_date combined

C The queryset is ordered first by author, then by published_date

D Raises an error because multiple order_by calls are not allowed

💡 Hint

Each order_by call overrides the previous ordering.

In Django, calling order_by multiple times replaces the previous ordering. Only the last order_by call applies.

❓ state_output

expert

What is the number of items in this sliced queryset?

If Entry.objects.all() returns 15 items, how many items does Entry.objects.order_by('-created_at')[3:10] contain?

A 12 items

B 6 items

C 10 items

D 7 items

💡 Hint

Count the items between indices 3 and 9 inclusive.

The slice [3:10] includes items at indices 3 through 9, which is 7 items total.