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Unlocking the Power of Cursor-Based Pagination
When it comes to interacting with vast amounts of data, some applications stand out from the rest. Take Facebook, for instance, where users continuously scroll through their newsfeeds, engaging with numerous friends and various items like shared posts and liked photos. In such scenarios, it’s impractical for the web or mobile app to request all new items at once from the API server. The resulting HTTP response payload would be enormous, leading to slow page loading.
The Solution: Pagination
To address this issue, pagination comes into play. By slicing the data a client asks for into “pages,” the resulting payloads become smaller and quicker to resolve, translating to significant performance gains for the client. Cursor-based pagination is a popular variant of this strategy, where the server sends “cursors” representing the position of each item in the dataset. The client uses these cursors to request data from the server and specify a limit on the amount.
The Benefits of Cursor-Based Pagination
While cursor-based pagination comes with some constraints, such as not being able to pass in a random page number in the middle of the dataset, it offers significant advantages. For instance, it supports new data insertions into the dataset during paging. Going back to the Facebook example, when a user scrolls through their newsfeed, new items like a new reaction to a post could enter the feed at any time. This makes the API schema more complex compared to what would be needed for a simple list.
Implementing Cursor-Based Pagination with Node.js and GraphQL
In this article, we’ll explore the features and benefits of cursor-based pagination and demonstrate how to implement a basic Node.js GraphQL server that provides a paginated dataset using the Apollo Server package and a simple database access layer.
Requirements for Cursor-Based Pagination
To provide cursor-based pagination, there are some essential factors to consider. One of the most critical aspects is that your data must contain a unique sequential column to base cursors on. Without one, ordering won’t be guaranteed for the API, and your client could receive different results with each request.
Setting Up the Node.js Development Environment
To start, let’s set up our workspace by installing Node.js and creating a new directory for our project. We’ll use the Apollo Server and LokiJS npm packages, which require a package.json file. We’ll add a start script to our package.json file and create a simple NOSQL database collection containing Luke Skywalker’s contacts.
Creating a NOSQL Database Collection
Our sample dataset has 10 items and a unique sequential column, Username. We’ll use the LokiJS in-memory database, which requires zero setup. The getFriends function includes the usernameCursor argument, which the client will use to ask for additional items besides just the Username.
Setting Up the Function to Query the Database
To get the list of Luke’s friends during pagination, we’ll need to set up a function to query the LokiJS database. We’ll write a function to seed the database and test the new function works by logging the debug function call.
Creating the GraphQL API Server Schema
Servers offering a GraphQL API can support cursor-based pagination. We’ll define our GraphQL schema inside the typeDefs variable, following the Relay GraphQL Cursor Connections Specification. This specification comes with benefits, such as clients being able to easily navigate our GraphQL API and learn how to paginate through the API server data quickly.
Setting Up the Apollo Server
With our schema implemented, the final piece is the server itself. We’ll bootstrap the Apollo Server, give it our schema, and implement the resolver. Our resolver will pass the arguments sent to the server to the database accessor, returning the list of friends needed for the response.
Seeing the GraphQL Cursor-Based Pagination in Action
With our server implemented, let’s query it with some sample queries that a client would send. We’ll open the link to localhost:4000, which will open the Apollo Sandbox, and copy and paste the example query into the “Operation” field. Clicking ExampleQuery will get the paginated friend data from the server, and we should see the last two items.
The Power of Cursor-Based Pagination
Cursor-based pagination is a powerful strategy for slicing data into “pages” and improving the performance of your application. By sending cursors with each item in the dataset, representing its position, and then using these cursors to ask the server for the data you want, you can significantly enhance the user experience. While it comes with some complexities, the benefits of cursor-based pagination make it an essential tool in your development arsenal.