How to implement cursor pagination using Sequelize

2 min read 07-10-2024

How to implement cursor pagination using Sequelize

Efficiently Paginate Your Data with Sequelize: A Guide to Cursor Pagination

Tired of inefficient limit-offset pagination and its inherent performance issues? Cursor pagination offers a more robust and scalable solution for fetching large datasets, especially when dealing with dynamically changing data. This guide dives into the world of cursor pagination with Sequelize, providing a practical implementation strategy and exploring its advantages over traditional methods.

The Problem with Limit-Offset Pagination

Let's imagine you have a large table storing user data, and you want to display this data on your website in a paginated manner. Limit-offset pagination is a common approach, where you fetch a fixed number of records (the limit) starting from a specified offset.

Here's a simplified example using Sequelize:

const { Op } = require('sequelize');

const users = await User.findAll({
    offset: 10, // Skip the first 10 users
    limit: 10,  // Fetch the next 10 users
});

The challenge? This method becomes unreliable when new data is inserted or deleted. Imagine a user is deleted between page loads: the offset will be inaccurate, potentially skipping or duplicating data.

Enter Cursor Pagination: A More Reliable Solution

Cursor pagination solves this issue by using a unique identifier (typically a timestamp or ID) to pinpoint the starting point of each page. This identifier, the "cursor," acts as a reference point, ensuring data consistency even with dynamic changes.

Implementing Cursor Pagination with Sequelize

Here's how to implement cursor pagination with Sequelize in a step-by-step approach:

Define a Cursor:
- Choose a unique identifier for your cursor. This could be a timestamp, an ID, or a combination of both.
- In this example, we'll use the createdAt timestamp for simplicity.
Fetch Initial Page:
- For the initial page, you won't need a cursor. Simply fetch your first set of data:
```
const initialPage = await User.findAll({
    limit: 10, // Fetch the first 10 users
});
```

Fetch Subsequent Pages:

For subsequent pages, pass the previous page's last cursor as the starting point:

const previousPageLastCursor = initialPage[initialPage.length - 1].createdAt; 

const nextPage = await User.findAll({
    where: {
        createdAt: { [Op.gt]: previousPageLastCursor },
    },
    limit: 10,
});

Handle Edge Cases:
- Empty Page: If nextPage is empty, it means you've reached the end of the dataset.
- Reverse Order: For descending order, simply change Op.gt to Op.lt in your where clause.

Advantages of Cursor Pagination

Stability: Cursor pagination ensures data consistency even if data is inserted or deleted between page loads.
Scalability: This method is well-suited for large datasets, as it efficiently handles changes in the underlying data.
Flexibility: You can easily change the ordering of your data without breaking pagination logic.

Conclusion: Embrace the Power of Cursor Pagination

By implementing cursor pagination with Sequelize, you gain a significant advantage in handling large datasets while maintaining data integrity and a smooth user experience. Remember to carefully choose your cursor identifier and handle edge cases for optimal performance. Embrace the power of cursor pagination and watch your application's scalability soar!