ruby 36 lines · 5 steps

Caching dashboard metrics in Rails

A service object wraps expensive account queries in Rails.cache with time-bucketed keys so results stay fresh but cheap.

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Rails Intermediate caching service-object query-optimization cache-keys time-bucketing
1class DashboardMetrics
2 CACHE_TTL = 15.minutes
3 
4 def initialize(account)
5 @account = account
6 end
7 
8 def monthly_recurring_revenue
9 Rails.cache.fetch(mrr_cache_key, expires_in: CACHE_TTL) do
10 @account.subscriptions
11 .active
12 .joins(:plan)
13 .sum("plans.amount_cents * subscriptions.quantity")
14 end
15 end
16 
17 def active_users_count
18 Rails.cache.fetch(active_users_cache_key, expires_in: CACHE_TTL) do
19 @account.users.where("last_seen_at > ?", 30.days.ago).count
20 end
21 end
22 
23 private
24 
25 def mrr_cache_key
26 ["account", @account.id, "mrr", current_bucket].join("/")
27 end
28 
29 def active_users_cache_key
30 ["account", @account.id, "active_users", current_bucket].join("/")
31 end
32 
33 def current_bucket
34 (Time.current.to_i / CACHE_TTL.to_i)
35 end
36end
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Wrapping expensive aggregate queries in Rails.cache.fetch trades a little staleness for large read savings.
  2. 2Embedding a time bucket in the cache key gives you automatic expiry aligned to a window without relying solely on TTL.
  3. 3A plain service object keeps caching logic out of models and controllers where it would otherwise sprawl.

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