Safe Pagination with Keyset (No OFFSET)

8880 views

                  class Comment < ApplicationRecord
  scope :newest_first, -> { order(created_at: :desc, id: :desc) }

  def self.after(cursor)
    return newest_first unless cursor
    where("(created_at, id) < (?, ?)", cursor.fetch(:created_at), cursor.fetch(:id)).newest_first
  end
end

                  class CommentsController < ApplicationController
  def index
    cursor = params[:cursor].present? ? JSON.parse(params[:cursor], symbolize_names: true) : nil
    @comments = Comment.after(cursor).limit(50)

    last = @comments.last
    @next_cursor = last ? { created_at: last.created_at.iso8601, id: last.id } : nil
  end
end

OFFSET gets slower as tables grow and becomes inconsistent under writes. Keyset pagination is stable and fast: paginate by (created_at, id) cursor. This is a common “senior Rails” upgrade for activity feeds.

Sarah Chen

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Safe Pagination with Keyset (No OFFSET)

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