ruby 39 lines · 7 steps

Cursor-based pagination in a Rails controller

A Rails index action paginates articles by ID cursor instead of page numbers, keeping results stable and queries efficient.

Explained by highlit
Rails Intermediate pagination cursor query-building input-validation json-api
1class ArticlesController < ApplicationController
2 DEFAULT_LIMIT = 25
3 MAX_LIMIT = 100
4 
5 def index
6 articles = Article.published.order(id: :desc).limit(page_limit)
7 articles = articles.where("articles.id < ?", cursor) if cursor
8 
9 records = articles.to_a
10 
11 render json: {
12 articles: records.map { |a| serialize(a) },
13 next_cursor: records.size == page_limit ? records.last.id : nil
14 }
15 end
16 
17 private
18 
19 def cursor
20 Integer(params[:cursor]) if params[:cursor].present?
21 rescue ArgumentError
22 nil
23 end
24 
25 def page_limit
26 limit = params.fetch(:limit, DEFAULT_LIMIT).to_i
27 limit = DEFAULT_LIMIT if limit <= 0
28 [limit, MAX_LIMIT].min
29 end
30 
31 def serialize(article)
32 {
33 id: article.id,
34 title: article.title,
35 slug: article.slug,
36 published_at: article.published_at.iso8601
37 }
38 end
39end
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STEP 01

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Three takeaways
  1. 1Cursor pagination uses a stable ordering key like a descending ID instead of offsets, so results don't shift when rows are inserted.
  2. 2Returning next_cursor only when a full page was fetched gives clients a clean signal for when to stop.
  3. 3Sanitizing limit and cursor params up front protects the query from bad input and abusive page sizes.

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