Add caching layer to metrics (#17617)

app/lib/admin/metrics/dimension/base_dimension.rb

@@ -1,23 +1,34 @@
 # frozen_string_literal: true
 
 class Admin::Metrics::Dimension::BaseDimension
+  CACHE_TTL = 5.minutes.freeze
+
   def self.with_params?
     false
   end
 
+  attr_reader :loaded
+
+  alias loaded? loaded
+
   def initialize(start_at, end_at, limit, params)
     @start_at = start_at&.to_datetime
     @end_at   = end_at&.to_datetime
     @limit    = limit&.to_i
     @params   = params
+    @loaded   = false
   end
 
   def key
     raise NotImplementedError
   end
 
+  def cache_key
+    ["metrics/dimension/#{key}", @start_at, @end_at, @limit, canonicalized_params].join(';')
+  end
+
   def data
-    raise NotImplementedError
+    load
   end
 
   def self.model_name
@@ -30,11 +41,28 @@ class Admin::Metrics::Dimension::BaseDimension
 
   protected
 
+  def load
+    unless loaded?
+      @values = Rails.cache.fetch(cache_key, expires_in: CACHE_TTL) { perform_query }
+      @loaded = true
+    end
+
+    @values
+  end
+
+  def perform_query
+    raise NotImplementedError
+  end
+
   def time_period
     (@start_at..@end_at)
   end
 
   def params
-    raise NotImplementedError
+    {}
+  end
+
+  def canonicalized_params
+    params.to_h.to_a.sort_by { |k, _v| k.to_s }.map { |k, v| "#{k}=#{v}" }.join(';')
   end
 end