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.