Pager

Cursor-based pagination (aka keyset pagination) is a common pagination strategy that avoids many of the pitfalls of “offset–limit” pagination.

For example, with offset–limit pagination, if an item from a prior page is deleted while the client is paginating, all subsequent results will be shifted forward by one. Therefore, when the client requests the next page, there’s one result that it will skip over and never see. Conversely, if a result is added to the list of results as the client is paginating, the client may see the same result multiple times, on different pages. Cursor-based pagination can prevent both of these possibilities.

Cursor-based pagination also performs better for large data sets under most implementations.

To support cursor-based pagination, this specification defines four query parameters after, before, limit, and sort

Add this line to your application's Gemfile:

gem 'rb_pager'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install rb_pager

Add the rb_pager.rb

If you use Rails, put it into the config/initializers dir

Once the gem installed on your project, usually you don't need to do anything. The system use Base64.strict_decode64 and Base64.strict_encode64 for cursor values

# return first 20 employee records, by default limit set to 20
Employee.pager

# return first 15 employee records
Employee.pager(limit: 15)

# return first 10 employee records order by created_at asc
# /employee?limit=10&sort=created_at
Employee.pager(after:  'w33t44==', limit:  10, sort:  'created_at')

# return first 10 employee records order by created_at desc
# /employee?limit=10&sort=-created_at
Employee.pager(after:  'w33t44==', limit:  10, sort:  '-created_at')

# [order by non uniq column](https://engineering.shopify.com/blogs/engineering/pagination-relative-cursors)
# /employee?limit=10&sort=name,id&after=w33t44==
Employee.pager(after:  'w33t44==', limit:  10, sort:  'name,id')

# /employee?limit=10&sort=name,id&before=w33t44==
Employee.pager(before:  'w33t44==', limit:  10, sort:  'name,id')

# on EmployeesController
records, meta = Employee.pager(limit:  15)
# meta => { prev_cursor => 'ergOW==' next_cursor => 'uahOI==' }
render  json: EmployeeSerializer.new(records, meta: meta).serialized_json, status:  :ok

• implement before cursor
• meta url for next and previous page
• meta url for first, last and collection size
• error-cases
• custom encoder

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/BambangSinaga/rb_pager. This project is intended to be a safe, welcoming space for collaboration, and contributors.

The gem is available as open source under the terms of the MIT License.