Ordering and slicing querysets in Django - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to order the queryset by the 'name' field in ascending order.

Django

products = Product.objects.all().order_by([1])

Drag options to blanks, or click blank then click option'

A'-name'

B'name'

C'price'

D'-price'

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-name' which sorts descending instead of ascending.

Using a field name that does not exist in the model.

Using order_by('name') sorts the queryset by the 'name' field in ascending order.

2fill in blank

medium

Complete the code to get the first 5 items from the queryset.

Django

top_products = Product.objects.all().order_by('rating')[1]

Drag options to blanks, or click blank then click option'

A[:5]

B[:10]

C[5:]

D[1:5]

Attempts:

3 left

💡 Hint

Common Mistakes

Using [5:] which skips the first 5 items instead of taking them.

Using [:10] which returns 10 items instead of 5.

Slicing with [:5] returns the first 5 items from the queryset.

3fill in blank

hard

Fix the error in the code to order by 'created_at' descending.

Django

recent_items = Item.objects.all().order_by([1])

Drag options to blanks, or click blank then click option'

A-created_at

B'created_at'

Ccreated_at

D'-created_at'

Attempts:

3 left

💡 Hint

Common Mistakes

Using the field name without quotes causing a NameError.

Using 'created_at' without minus sign which orders ascending.

To order descending by a field, use a string with a minus sign: '-created_at'.

4fill in blank

hard

Fill both blanks to get items ordered by 'price' ascending and slice to get items 10 to 20.

Django

items = Product.objects.all().order_by([1])[2]

Drag options to blanks, or click blank then click option'

A'price'

B[:10]

C[10:20]

D'-price'

Attempts:

3 left

💡 Hint

Common Mistakes

Using descending order '-price' instead of ascending.

Using slice [:10] which gets the first 10 items instead of items 10 to 20.

Use order_by('price') to sort ascending by price, and slice [10:20] to get items from index 10 up to 19.

5fill in blank

hard

Fill all three blanks to order by 'category' ascending, then by 'name' descending, and slice the first 15 items.

Django

products = Product.objects.all().order_by([1], [2])[3]

Drag options to blanks, or click blank then click option'

A'category'

B'-name'

C[:15]

D'name'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'name' instead of '-name' for descending order.

Not slicing or slicing incorrectly to get the first 15 items.

Ordering by multiple fields uses multiple strings in order_by. Use 'category' for ascending and '-name' for descending. Slice with [:15] to get the first 15 items.

Practice

1. What does the Django queryset method order_by('name') do?

easy

A. Groups the queryset results by the 'name' field.

B. Filters the queryset to only include objects with the name 'order_by'.

C. Sorts the queryset results by the 'name' field in ascending order.

D. Deletes all objects that have a 'name' field.

Solution

1. Step 1: Understand the order_by() method

   The order_by() method sorts the queryset results based on the given field(s).

2. Step 2: Apply order_by('name')

   This sorts the results by the 'name' field in ascending order by default.

3. Final Answer:

   Sorts the queryset results by the 'name' field in ascending order. -> Option C

4. Quick Check:

   order_by('name') = sorted by name ascending [OK]

Hint: Remember: order_by sorts, does not filter or delete [OK]

Common Mistakes:

• Confusing order_by with filter
• Thinking order_by deletes data
• Assuming order_by groups data

2. Which of the following is the correct syntax to get the first 5 objects ordered by 'created_at' descending?

easy

A. Model.objects.order_by('-created_at')[:5]

B. Model.objects[:5].order_by('-created_at')

C. Model.objects.order_by('created_at')[:5]

D. Model.objects.order_by('created_at')[-5:]

Solution

1. Step 1: Use order_by('-created_at') for descending order

   Prefixing the field with '-' sorts descending.

2. Step 2: Slice the queryset with [:5] to get first 5 results

   Slicing before evaluation limits results to first 5.

3. Final Answer:

   Model.objects.order_by('-created_at')[:5] -> Option A

4. Quick Check:

   Descending order + first 5 = order_by('-field')[:5] [OK]

Hint: Use '-' before field for descending order, slice after ordering [OK]

Common Mistakes:

• Slicing before ordering (wrong order)
• Missing '-' for descending order
• Using negative slice like [-5:] incorrectly

3. Given the queryset qs = Model.objects.order_by('age')[2:5], what will list(qs) return if the ages in the database are [20, 25, 30, 35, 40, 45]?

medium

A. [25, 30, 35]

B. [30, 35, 40]

C. [35, 40, 45]

D. [20, 25, 30]

Solution

1. Step 1: Order the ages ascending

   Ordering by 'age' gives [20, 25, 30, 35, 40, 45].

2. Step 2: Slice from index 2 to 5 (excluding 5)

   Indexes 2, 3, 4 correspond to ages 30, 35, 40.

3. Final Answer:

   [30, 35, 40] -> Option B

4. Quick Check:

   order_by + slice = [30, 35, 40] [OK]

Hint: Remember slicing excludes the end index [OK]

Common Mistakes:

• Including the end index in slice
• Mixing up ascending and descending order
• Using wrong slice indexes

4. What is wrong with this queryset code?

qs = Model.objects[:5].order_by('name')

medium

A. You cannot slice a queryset before ordering; slicing must come after ordering.

B. The queryset must be filtered before ordering.

C. The order_by method requires a list, not a string.

D. Slicing with [:5] returns a list, so order_by cannot be called after.

Solution

1. Step 1: Understand queryset slicing returns a list

   Slicing a queryset like Model.objects[:5] evaluates it and returns a list, not a queryset.

2. Step 2: Calling order_by on a list causes error

   Lists do not have order_by method, so this code raises an error.

3. Final Answer:

   Slicing with [:5] returns a list, so order_by cannot be called after. -> Option D

4. Quick Check:

   Slice first = list, no order_by after [OK]

Hint: Always order before slicing to keep queryset chainable [OK]

Common Mistakes:

• Slicing before ordering
• Thinking order_by accepts lists
• Confusing filter and order_by order

5. You want to get the 3rd to 7th newest entries from a model ordered by 'published_date' descending. Which queryset code is correct?

hard

A. Model.objects.order_by('-published_date')[2:7]

B. Model.objects.order_by('published_date')[3:8]

C. Model.objects[2:7].order_by('-published_date')

D. Model.objects.order_by('-published_date')[3:8]

Solution

1. Step 1: Order by 'published_date' descending

   Use order_by('-published_date') to get newest first.

2. Step 2: Slice from index 2 to 7 to get 3rd to 7th entries

   Slicing [2:7] gets items at indexes 2,3,4,5,6 (5 items total).

3. Final Answer:

   Model.objects.order_by('-published_date')[2:7] -> Option A

4. Quick Check:

   Descending order + slice 2:7 = 3rd to 7th newest [OK]

Hint: Order descending first, then slice with zero-based indexes [OK]

Common Mistakes:

• Using ascending order instead of descending
• Slicing with wrong indexes (off by one)
• Slicing before ordering