ruby 60 lines · 9 steps

Building a paginated activity feed in Rails

A single class merges several ActiveRecord sources into one sorted, paginated, renderable stream.

Explained by highlit
Rails Intermediate enumerable pagination composition struct view-rendering
1class ActivityFeed
2 include Enumerable
3 
4 Entry = Struct.new(:record, :type, :occurred_at, keyword_init: true) do
5 def to_partial_path
6 "activities/#{type}"
7 end
8 end
9 
10 DEFAULT_PER_PAGE = 25
11 
12 def initialize(user, page: 1, per_page: DEFAULT_PER_PAGE)
13 @user = user
14 @page = [page.to_i, 1].max
15 @per_page = per_page.to_i.clamp(1, 100)
16 end
17 
18 def each(&block)
19 entries.each(&block)
20 end
21 
22 def entries
23 @entries ||= merged.slice(offset, @per_page) || []
24 end
25 
26 def next_page?
27 merged.size > offset + @per_page
28 end
29 
30 def next_page
31 next_page? ? @page + 1 : nil
32 end
33 
34 private
35 
36 def offset
37 (@page - 1) * @per_page
38 end
39 
40 def merged
41 @merged ||= sources
42 .flat_map { |type, scope| wrap(scope, type) }
43 .sort_by { |entry| -entry.occurred_at.to_i }
44 end
45 
46 def sources
47 limit = offset + @per_page
48 {
49 comment: @user.comments.recent.limit(limit),
50 post: @user.posts.published.recent.limit(limit),
51 follow: @user.received_follows.recent.limit(limit)
52 }
53 end
54 
55 def wrap(scope, type)
56 scope.map do |record|
57 Entry.new(record: record, type: type, occurred_at: record.created_at)
58 end
59 end
60end
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Including Enumerable and defining each gives your object the full collection API for free.
  2. 2Normalizing heterogeneous records into a common Struct lets you merge and sort them uniformly.
  3. 3Memoization plus bounded input sizes keeps a multi-source feed cheap to build and safe to paginate.

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