Cursor-based pagination in Rest API - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is cursor-based pagination?

Cursor-based pagination is a method to split large sets of data into smaller parts using a unique identifier (cursor) to mark the position for the next set of results.

intermediate

How does cursor-based pagination differ from offset-based pagination?

Cursor-based pagination uses a unique cursor to track the current position, making it more efficient and reliable for large or changing datasets, while offset-based pagination uses page numbers and offsets which can cause duplicates or missing data if the dataset changes.

beginner

What is a typical structure of a cursor in cursor-based pagination?

A cursor is usually an encoded string representing a unique value like a timestamp or an ID from the last item in the current page, which the server uses to fetch the next set of results.

intermediate

Why is cursor-based pagination better for real-time data?

Because it uses a stable cursor to mark the last seen item, it avoids skipping or repeating items even if new data is added or removed while paginating.

advanced

What is a common challenge when implementing cursor-based pagination?

A common challenge is designing a cursor that is both secure and opaque, so users cannot guess or manipulate it, often requiring encoding or encryption.

What does a cursor represent in cursor-based pagination?

A The size of each page

B The total number of pages

C A unique position marker for the next page

D The current page number

The cursor marks the position in the data to fetch the next set of results.

Which problem does cursor-based pagination solve better than offset-based pagination?

A Handling data changes during pagination

B Displaying total number of pages

C Sorting data alphabetically

D Caching static pages

Cursor-based pagination handles data changes without skipping or repeating items.

What is usually encoded in a cursor string?

A Page size

B User password

C Total number of items

D Unique ID or timestamp of the last item

The cursor encodes a unique identifier like an ID or timestamp to mark position.

Why might cursor-based pagination be more secure when the cursor is encoded?

A Prevents users from guessing or changing the cursor

B Makes the API faster

C Allows unlimited page sizes

D Shows total item count

Encoding the cursor keeps it opaque and prevents tampering.

Which is a typical use case for cursor-based pagination?

A Displaying static product catalogs

B Loading social media feeds

C Showing a fixed list of countries

D Printing a PDF report

Social media feeds often update in real-time, making cursor pagination ideal.

Explain how cursor-based pagination works and why it is useful for APIs dealing with large or changing data.

Think about how you keep track of where you left off in a long list.

Describe the difference between cursor-based and offset-based pagination and when you might choose one over the other.

Consider what happens if new items are added while you browse pages.

Practice

1.

What is the main purpose of cursor-based pagination in REST APIs?

easy

A. To sort data alphabetically before sending

B. To efficiently fetch the next set of data using a marker

C. To cache all data on the client side

D. To send all data in a single response

Solution

1. Step 1: Understand cursor-based pagination concept

   Cursor-based pagination uses a marker (cursor) to fetch the next set of data instead of page numbers.

2. Step 2: Identify the main purpose

   This method helps efficiently retrieve data in chunks and avoid missing or repeating items when data changes.

3. Final Answer:

   To efficiently fetch the next set of data using a marker -> Option B

4. Quick Check:

   Cursor-based pagination = fetch next data with marker [OK]

Hint: Cursor marks position to get next data chunk [OK]

Common Mistakes:

• Confusing cursor with page number
• Thinking it sends all data at once
• Assuming it sorts data alphabetically

2.

Which of the following is the correct way to include a cursor in a REST API request URL?

GET /items?____=abc123

easy

A. cursor

B. limit

C. page

D. offset

Solution

1. Step 1: Identify the query parameter for cursor

   Cursor-based pagination uses a parameter named cursor to mark the position for the next data fetch.

2. Step 2: Match the parameter in the URL

   The URL should include ?cursor=abc123 to pass the cursor value.

3. Final Answer:

   cursor -> Option A

4. Quick Check:

   Cursor parameter in URL = cursor [OK]

Hint: Cursor parameter is usually named 'cursor' [OK]

Common Mistakes:

• Using 'page' or 'offset' which are for offset pagination
• Confusing 'limit' with cursor
• Leaving out the cursor parameter

3.

Given this API response for cursor-based pagination:

{
  "data": ["item4", "item5"],
  "next_cursor": "xyz789"
}

What should the client do to get the next page of data?

medium

A. Send a request with ?cursor=xyz789

B. Send a request with ?page=2

C. Send a request with ?offset=2

D. Send a request with ?limit=2

Solution

1. Step 1: Read the response for next cursor

   The response includes a next_cursor value "xyz789" which marks the next data position.

2. Step 2: Use the cursor in the next request

   The client should send a request with ?cursor=xyz789 to get the next page.

3. Final Answer:

   Send a request with ?cursor=xyz789 -> Option A

4. Quick Check:

   Use next_cursor value as cursor parameter [OK]

Hint: Use next_cursor value as cursor in next request [OK]

Common Mistakes:

• Using page or offset parameters instead of cursor
• Ignoring next_cursor and repeating last request
• Sending limit without cursor

4.

Consider this code snippet for fetching paginated data using cursor-based pagination:

cursor = None
while True:
    response = api.get_items(cursor=cursor)
    process(response.data)
    cursor = response.next_cursor
    if not cursor:
        break

What is the likely bug in this code?

medium

A. It processes data before fetching

B. It does not check if next_cursor exists before assigning

C. It never updates the cursor value

D. It may cause an infinite loop if next_cursor is empty string

Solution

1. Step 1: Analyze the code structure

   The code fetches data, processes it, then assigns cursor = response.next_cursor without checking if next_cursor is empty string.

2. Step 2: Potential infinite loop

   If next_cursor is an empty string, the condition if not cursor will be true and break the loop, so no infinite loop occurs. But if the check is incorrect or cursor is None, it breaks. However, the main issue is if next_cursor is missing, it raises an error.

3. Step 3: Proper handling

   Should check if next_cursor exists and is truthy before assigning and breaking.

4. Final Answer:

   It may cause an infinite loop if next_cursor is empty string -> Option D

5. Quick Check:

   Check for empty or missing cursor carefully [OK]

Hint: Check for empty or missing cursor carefully [OK]

Common Mistakes:

• Assuming next_cursor always exists
• Not breaking loop on missing cursor
• Updating cursor after break

5.

You have an API that returns data with cursor-based pagination. The API returns the following responses in sequence:

1. {"data": ["a", "b"], "next_cursor": "c1"}
2. {"data": ["c", "d"], "next_cursor": "c2"}
3. {"data": ["e"], "next_cursor": null}

You want to collect all items without duplicates even if the API sometimes returns overlapping data due to data changes. Which approach is best?

hard

A. Collect all items in a list and remove duplicates after fetching all pages

B. Fetch only the first page to avoid duplicates

C. Use a set to store items as you fetch each page to avoid duplicates immediately

D. Ignore duplicates and trust API never repeats data

Solution

1. Step 1: Understand overlapping data issue

   Cursor-based pagination can return overlapping items if data changes during pagination, causing duplicates.

2. Step 2: Choose a method to avoid duplicates

   Using a set to store items as they are fetched avoids duplicates immediately and efficiently.

3. Step 3: Evaluate other options

   Removing duplicates after fetching all pages (list) is less efficient. Ignoring duplicates or fetching only first page is incorrect.

4. Final Answer:

   Use a set to store items as you fetch each page to avoid duplicates immediately -> Option C

5. Quick Check:

   Use set to avoid duplicates during fetch [OK]

Hint: Use set to track unique items during pagination [OK]

Common Mistakes:

• Assuming API never returns duplicates
• Removing duplicates only after all data fetched
• Fetching only first page to avoid duplicates