Pagination links in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this pagination link generation code?

Consider a REST API that returns paginated results. The following Python code generates pagination links for a given page and total pages.

def get_pagination_links(current_page, total_pages):
    base_url = 'https://api.example.com/items?page='
    links = {}
    if current_page > 1:
        links['prev'] = base_url + str(current_page - 1)
    if current_page < total_pages:
        links['next'] = base_url + str(current_page + 1)
    links['self'] = base_url + str(current_page)
    return links

print(get_pagination_links(3, 5))

What will be printed?

Rest API

def get_pagination_links(current_page, total_pages):
    base_url = 'https://api.example.com/items?page='
    links = {}
    if current_page > 1:
        links['prev'] = base_url + str(current_page - 1)
    if current_page < total_pages:
        links['next'] = base_url + str(current_page + 1)
    links['self'] = base_url + str(current_page)
    return links

print(get_pagination_links(3, 5))

A {"prev": "https://api.example.com/items?page=2", "next": "https://api.example.com/items?page=4", "self": "https://api.example.com/items?page=3"}

B {"prev": "https://api.example.com/items?page=3", "next": "https://api.example.com/items?page=4", "self": "https://api.example.com/items?page=3"}

C {"prev": "https://api.example.com/items?page=2", "self": "https://api.example.com/items?page=3"}

D {"next": "https://api.example.com/items?page=4", "self": "https://api.example.com/items?page=3"}

💡 Hint

Think about which pages exist before and after the current page 3 when total pages are 5.

The code adds a 'prev' link only if the current page is greater than 1, so page 2 is included. It adds a 'next' link only if current page is less than total pages, so page 4 is included. The 'self' link is always included for the current page 3.

❓ Predict Output

intermediate

What error does this pagination link code raise?

Look at this JavaScript function that generates pagination links:

function getPaginationLinks(currentPage, totalPages) {
  const baseUrl = 'https://api.example.com/items?page=';
  const links = {};
  if (currentPage > 1) {
    links.prev = baseUrl + (currentPage - 1);
  }
  if (currentPage < totalPages) {
    links.next = baseUrl + (currentPage + 1);
  }
  links.self = baseUrl + currentPage;
  return links;
}

console.log(getPaginationLinks(0, 5));

What error or output will this code produce?

Rest API

function getPaginationLinks(currentPage, totalPages) {
  const baseUrl = 'https://api.example.com/items?page=';
  const links = {};
  if (currentPage > 1) {
    links.prev = baseUrl + (currentPage - 1);
  }
  if (currentPage < totalPages) {
    links.next = baseUrl + (currentPage + 1);
  }
  links.self = baseUrl + currentPage;
  return links;
}

console.log(getPaginationLinks(0, 5));

A TypeError: Cannot read property 'prev' of undefined

B {"prev": "https://api.example.com/items?page=-1", "next": "https://api.example.com/items?page=1", "self": "https://api.example.com/items?page=0"}

C {"next": "https://api.example.com/items?page=1", "self": "https://api.example.com/items?page=0"}

D SyntaxError: Unexpected token

💡 Hint

Check the conditions for adding 'prev' and 'next' links when currentPage is 0.

Since currentPage is 0, the condition currentPage > 1 is false, so 'prev' is not added. currentPage < totalPages is true, so 'next' is added with page 1. 'self' is always added with page 0. No error occurs.

🔧 Debug

advanced

Why does this pagination link code raise a KeyError?

In Python, this code tries to access pagination links but raises a KeyError:

def get_links(page, total):
    base = 'https://api.example.com/items?page='
    links = {'self': base + str(page)}
    if page > 1:
        links['prev'] = base + str(page - 1)
    if page < total:
        links['next'] = base + str(page + 1)

print(links['prev'])

Why does this raise a KeyError?

Rest API

def get_links(page, total):
    base = 'https://api.example.com/items?page='
    links = {'self': base + str(page)}
    if page > 1:
        links['prev'] = base + str(page - 1)
    if page < total:
        links['next'] = base + str(page + 1)

print(links['prev'])

A Because 'links' is defined inside the function but accessed outside, causing NameError

B Because 'links' is a list, not a dictionary, so keys are invalid

C Because 'links' dictionary is empty, so 'prev' key is missing

D Because 'prev' key may not exist if page is 1, causing KeyError

💡 Hint

Check where the variable 'links' is defined and where it is accessed.

The variable 'links' is created inside the function get_links but the print statement tries to access it outside the function scope, so 'links' is not defined there, causing a NameError, not a KeyError. The question states KeyError, but the actual error is NameError.

❓ Predict Output

advanced

What is the output of this SQL query for pagination links?

Given a table items with 100 rows, this SQL query tries to get pagination info for page 3 with 10 items per page:

WITH total_count AS (
  SELECT COUNT(*) AS total FROM items
),
page_info AS (
  SELECT 3 AS current_page, 10 AS per_page FROM dual
)
SELECT
  current_page,
  per_page,
  total,
  CASE WHEN current_page > 1 THEN current_page - 1 ELSE NULL END AS prev_page,
  CASE WHEN current_page * per_page < total THEN current_page + 1 ELSE NULL END AS next_page
FROM page_info, total_count;

What will be the values of prev_page and next_page in the result?

Rest API

WITH total_count AS (
  SELECT COUNT(*) AS total FROM items
),
page_info AS (
  SELECT 3 AS current_page, 10 AS per_page FROM dual
)
SELECT
  current_page,
  per_page,
  total,
  CASE WHEN current_page > 1 THEN current_page - 1 ELSE NULL END AS prev_page,
  CASE WHEN current_page * per_page < total THEN current_page + 1 ELSE NULL END AS next_page
FROM page_info, total_count;

A prev_page = 2, next_page = NULL

B prev_page = 2, next_page = 4

C prev_page = 3, next_page = 4

D prev_page = NULL, next_page = 4

💡 Hint

Calculate if current_page * per_page is less than total rows to determine next_page.

Current page is 3, per page 10, so 3*10=30 which is less than total 100, so next_page is 4. Since current_page > 1, prev_page is 2.

🚀 Application

expert

How many pagination links are generated for the last page?

In a REST API, a function generates pagination links for a list of 50 items with 10 items per page. The current page is 5 (the last page). The function adds 'prev' if current page > 1, 'next' if current page < total pages, and always adds 'self'.

How many links will be in the returned dictionary for page 5?

Rest API

def pagination_links(current_page, total_items, per_page):
    total_pages = (total_items + per_page - 1) // per_page
    base = 'https://api.example.com/items?page='
    links = {}
    if current_page > 1:
        links['prev'] = base + str(current_page - 1)
    if current_page < total_pages:
        links['next'] = base + str(current_page + 1)
    links['self'] = base + str(current_page)
    return links

result = pagination_links(5, 50, 10)
print(len(result))

A 4

B 1

C 3

D 2

💡 Hint

Calculate total pages and check conditions for 'prev' and 'next' links on the last page.

Total pages = 50/10 = 5. Current page is 5, so 'prev' link is added (page 4), 'next' link is not added because current page is last. 'self' is always added. So total 2 links.

Practice

1. What is the main purpose of pagination links in a REST API?

easy

A. To split large data into smaller pages for easier access

B. To encrypt the data sent from the server

C. To speed up the server response time by caching

D. To validate user authentication tokens

Solution

1. Step 1: Understand pagination concept

   Pagination divides large data sets into smaller, manageable pages.

2. Step 2: Identify purpose of pagination links

   Pagination links help clients navigate between these pages easily.

3. Final Answer:

   To split large data into smaller pages for easier access -> Option A

4. Quick Check:

   Pagination = split data into pages [OK]

Hint: Pagination means breaking data into pages for easy reading [OK]

Common Mistakes:

• Confusing pagination with data encryption
• Thinking pagination speeds up server response
• Mixing pagination with authentication

2. Which of the following is the correct syntax for a pagination link in an HTTP header?

easy

A. Link: ; rel="next"

B. Link: https://api.example.com/items?page=2 rel=next

C. Link: rel=next

D. Link: https://api.example.com/items?page=2; rel="next"

Solution

1. Step 1: Review correct Link header format

   The URL must be enclosed in angle brackets <> and rel value in quotes.

2. Step 2: Match syntax with options

   Link: ; rel="next" correctly uses <URL> and rel="next" with quotes.

3. Final Answer:

   Link: <https://api.example.com/items?page=2>; rel="next" -> Option A

4. Quick Check:

   Link header syntax = <URL>; rel="value" [OK]

Hint: Use angle brackets for URL and quotes for rel value [OK]

Common Mistakes:

• Omitting angle brackets around URL
• Not quoting the rel attribute value
• Missing semicolon between URL and rel

3. Given the HTTP Link header:
Link: <https://api.example.com/items?page=3>; rel="next", <https://api.example.com/items?page=1>; rel="prev"
What URL should the client use to get the previous page?

medium

A. https://api.example.com/items?page=3

B. https://api.example.com/items?page=4

C. https://api.example.com/items?page=1

D. https://api.example.com/items?page=2

Solution

1. Step 1: Identify rel attributes in Link header

   Rel="next" points to page 3, rel="prev" points to page 1.

2. Step 2: Find URL for previous page

   The client should use the URL with rel="prev", which is page 1.

3. Final Answer:

   https://api.example.com/items?page=1 -> Option C

4. Quick Check:

   Prev page URL = page=1 [OK]

Hint: Look for rel="prev" to find previous page URL [OK]

Common Mistakes:

• Choosing the next page URL instead of previous
• Confusing page numbers in URLs
• Ignoring rel attribute values

4. You receive this Link header:
Link: https://api.example.com/items?page=2; rel="next"
Why might this cause an error when parsing pagination links?

medium

A. The page number is invalid

B. The rel attribute value is missing quotes

C. The semicolon is missing between URL and rel

D. The URL is not enclosed in angle brackets

Solution

1. Step 1: Check Link header syntax rules

   URLs must be enclosed in angle brackets <> for correct parsing.

2. Step 2: Identify error in given header

   The URL is not inside <>, which can cause parsing errors.

3. Final Answer:

   The URL is not enclosed in angle brackets -> Option D

4. Quick Check:

   URL must be in <> for Link header [OK]

Hint: Always put URLs in angle brackets in Link headers [OK]

Common Mistakes:

• Forgetting angle brackets around URLs
• Assuming quotes around rel are optional
• Misplacing semicolons in header

5. You want to implement pagination links for an API returning 100 items with 10 items per page. Which Link header correctly provides navigation for page 5?

hard

A. Link: ; rel="next", ; rel="prev"

B. Link: ; rel="next", ; rel="prev"

C. Link: ; rel="next", ; rel="prev"

D. Link: ; rel="next", ; rel="prev"

Solution

1. Step 1: Calculate next and previous pages for page 5

   Next page after 5 is 6, previous page before 5 is 4.

2. Step 2: Match correct URLs with rel attributes

   Link: ; rel="next", ; rel="prev" correctly assigns page=6 to rel="next" and page=4 to rel="prev".

3. Final Answer:

   Link: <https://api.example.com/items?page=6>; rel="next", <https://api.example.com/items?page=4>; rel="prev" -> Option B

4. Quick Check:

   Page 5 next=6, prev=4 [OK]

Hint: Next page = current +1, prev page = current -1 in Link header [OK]

Common Mistakes:

• Swapping next and prev URLs
• Using current page number for both next and prev
• Incorrect page numbers outside valid range