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Introduction

Rekapager is a pagination library for PHP, supporting both offset-based and keyset-based pagination (also called cursor-based pagination).

Keyset Pagination (or Cursor-Based Pagination)​

Keyset pagination is a method of pagination that uses the last row of the current page as an anchor for the next page. This method has these advantages compared to the traditional offset-based pagination:

  • It is more efficient because it leverages the index. It does not require the database to scan all rows from the beginning to reach the desired page.
  • It is more resilient to data changes. The data will not drift when rows are inserted or deleted.

Identifying Pages​

Instead of using page numbers, a page identifier object is used to reference a page. This identifier is encoded into a string and passed as a single query parameter.

Because it requires only a single query parameter, it works similarly on the surface with offset pagination. Migrating from offset pagination to keyset pagination will be straightforward. The difference is that instead of having page numbers in the URL, we'll be getting an 'ugly' identifier, which is opaque to the user, but meaningful to the application.

It also easily allows us to keep the pagination job separate from the filtering and sorting logic. The library does not require a specific way to filter or sort your data.

Queries​

Multiple sort columns are supported. The library will automatically generate the WHERE query for you, including the complex cases involving more than two sort columns. The only requirement is that the query needs to have a deterministic sort order.

Some backends also have the option to use SQL row values syntax for a slightly better performance.

Bidirectional Navigation and Page Skipping​

Bidirectional navigation is supported. The user will be able to navigate forward and backward from the current page. It also supports offset seeking, allowing the user to skip the immediate next or previous page up to the configured proximity setting.

In the user interface, the pager will look like a regular pagination control:

with pages around the current page

The page number is informational only, and carried over from the start page.

Jumping to the Last Page​

Seeking to the last page is possible. And with keyset pagination, it will be as fast as seeking to the first page:

last page

Page Numbers and Counting​

Negative page numbers shown above indicate the page numbers from the end. The last page is -1, the second to last is -2, and so on. It is done this way because by default the pager does not fetch the total count from the underlying data, which is another common performance issue involving pagination.

The pager can work without knowing the total count, but if the count is available, the pager will use it:

last page with count

It can query the count from the underlying data, or the caller can supply the count. The count can also be an approximation, and the pager will work without an exact count.

Offset Pagination​

The library also supports the traditional offset pagination method with several important improvements.

No Counting by Default​

It can paginate without the total count of the data. If the count is not known, the pager won't allow the user to navigate to the last page:

no last page

As with keyset pagination, the count can be supplied by the caller, or the pager can query the count from the underlying data.

Page Number Limit​

It also limits the maximum page number that can be navigated to. By default, the limit is 100. The UI will indicate that the disabled page exists, but the user is not allowed to navigate to it:

page limit

This limit can be configured, or disabled entirely. But if you need the function to seek beyond a certain number of pages, you should consider switching to keyset pagination instead.

Pagerfanta Interoperability​

For interoperability, the library supports offset pagination using any of the existing Pagerfanta adapters, as well as adapting a Pagerfanta instance into an OffsetPageableInterface instance.

Same Interface for Both Offset and Keyset Pagination​

Both offset pagination and keyset pagination use the same interface. This allows you to keep using offset pagination and later switch to keyset pagination without too much effort.

Secure by Default (or Prevents AI Crawlers from Wreaking Havoc)​

With keyset pagination, not counting by default, and limiting pages in offset pagination, the library is secure by default. It prevents denials of service, either maliciously or accidentally. In most cases, a real user won't have a good reason for accessing page 56267264, but doing so can cause a denial of service to the web server, application, and the database.

After the AI craze, there is a surge of web crawlers that are looking for contents for AI training. Unlike traditional search engine crawlers, these new crawlers tend to be much dumber and much less respectful. Some would foolishly traverse thousands of paginated contents with a sub-second delay, causing a denial of service to the server. If your application is public and uses pagination, this library can help to prevent this problem.

Supported Data Types​

  • Doctrine Collections Selectable and Collection
  • Doctrine ORM QueryBuilder and NativeQuery
  • Doctrine DBAL QueryBuilder
  • Pagerfanta adapters

Framework Integrations​

  • Symfony
  • API Platform

Demo​

You can try the demo by running the following command:

docker run --rm -p 8187:80 ghcr.io/rekalogika/rekapager:latest

Then access the demo at http://localhost:8187.

Acknowledgements​

License​

MIT

Contributing​

This framework consists of multiple repositories split from a monorepo. Be sure to submit issues and pull requests to the rekalogika/rekapager monorepo.