Cursor based pagination for Rails models.

README.md

Example Usage

Users

id	name
1	Jane
2	Max
3	John
4	Scott
5	Mark

result = User.after(3) 
=>
[
  { id: 4, name: "Scott" },
  { id: 5, name: "Mark" }
]

result.has_more?
=> false

result.total_size
=> 2

result.total_count
=> 6

result = User.before(3) 
=>
[
  { id: 2, name: "Max" },
  { id: 1, name: "Jane" }
]

result.has_more?
=> false

result.total_size
=> 2

result.total_count
=> 6

result = User.after(1).limit(1)
=>
[
  { id: 2, name: "Max" }
]

result.has_more?
=> true

result.total_size
=> 5

result.total_count
=> 6

result = User.after(1).before(3)
=>
[
  { id: 2, name: "Max" }
]

result.has_more?
=> false

result.total_size
=> 1

result.total_count
=> 6

paginatable.rb

module Arel
  module Nodes
    module Cursor
      class LessThan < Arel::Nodes::LessThan; end
      class GreaterThan < Arel::Nodes::GreaterThan; end
    end
  end

  module Predications
    def before right
      Nodes::Cursor::LessThan.new self, quoted_node(right)
    end

    def after right
      Nodes::Cursor::GreaterThan.new self, quoted_node(right)
    end
  end
end

module Paginatable
  extend ActiveSupport::Concern

  included do
    def self.all(*args)
      super.extending(ActiveRecordRelationMethods)
    end

    def self.after(cursor)
      reorder(primary_key => :asc).where(
        arel_table[primary_key].after(cursor)
      ).extending(ActiveRecordRelationMethods)
    end

    def self.before(cursor)
      reorder(primary_key => :desc).where(
        arel_table[primary_key].before(cursor)
      ).extending(ActiveRecordRelationMethods)
    end
  end

  module ActiveRecordRelationMethods
    def has_more?
      @has_more ||= begin
        # Cache #size otherwise multiple calls to the database will occur.
        (results_size = size) > 0 && results_size < total_size
      end
    end

    # Returns number of records that exist in scope of the current cursor
    def total_size(column_name = :all) #:nodoc:
      # #count overrides the #select which could include generated columns
      # referenced in #order, so skip #order here, where it's irrelevant to the
      # result anyway.
      @total_size ||= begin
        context = except(:offset, :limit, :order)

        # Remove includes only if they are irrelevant
        context = context.except(:includes) unless references_eager_loaded_tables?

        args = [column_name]

        # .group returns an OrderedHash that responds to #count
        context = context.count(*args)

        if context.is_a?(Hash) || context.is_a?(ActiveSupport::OrderedHash)
          context.count
        else
          context.respond_to?(:count) ? context.count(*args) : context
        end
      end
    end
  
    # Returns number of records that exist without :offset, :limit, :order, :before or :after 
    def total_count(column_name = :all) #:nodoc:
      # #count overrides the #select which could include generated columns
      # referenced in #order, so skip #order here, where it's irrelevant to the
      # result anyway.
      @total_count ||= begin
        context = except(:offset, :limit, :order)

        context.where_values = where_values.reject do |value|
          value.is_a?(Arel::Nodes::Cursor::GreaterThan) ||
          value.is_a?(Arel::Nodes::Cursor::LessThan)
        end

        # Remove includes only if they are irrelevant
        context = context.except(:includes) unless references_eager_loaded_tables?

        args = [column_name]

        # .group returns an OrderedHash that responds to #count
        context = context.count(*args)

        if context.is_a?(Hash) || context.is_a?(ActiveSupport::OrderedHash)
          context.count
        else
          context.respond_to?(:count) ? context.count(*args) : context
        end
      end
    end
  end
end

@jerrygreen you can always sort by name, id.