PERF: Allow preloading 'recent time read' for a user (#9076)

This will be used when serializing multiple user cards

app/models/user.rb

@@ -1211,10 +1211,22 @@ class User < ActiveRecord::Base
     self.user_emails.secondary.pluck(:email)
   end
 
+  RECENT_TIME_READ_THRESHOLD ||= 60.days
+
+  def self.preload_recent_time_read(users)
+    times = UserVisit.where(user_id: users.map(&:id))
+      .where('visited_at >= ?', RECENT_TIME_READ_THRESHOLD.ago)
+      .group(:user_id)
+      .sum(:time_read)
+    users.each { |u| u.preload_recent_time_read(times[u.id] || 0) }
+  end
+
+  def preload_recent_time_read(time)
+    @recent_time_read = time
+  end
+
   def recent_time_read
-    self.created_at && self.created_at < 60.days.ago ?
-      self.user_visits.where('visited_at >= ?', 60.days.ago).sum(:time_read) :
-      self.user_stat&.time_read
+    @recent_time_read ||= self.user_visits.where('visited_at >= ?', RECENT_TIME_READ_THRESHOLD.ago).sum(:time_read)
   end
 
   def from_staged?

spec/models/user_spec.rb

@@ -2287,4 +2287,32 @@ describe User do
       expect(user.approved).to eq(true)
     end
   end
+
+  describe "#recent_time_read" do
+    fab!(:user) { Fabricate(:user) }
+    fab!(:user2) { Fabricate(:user) }
+
+    before_all do
+      UserVisit.create(user_id: user.id, visited_at: 1.minute.ago, posts_read: 1, mobile: false, time_read: 10)
+      UserVisit.create(user_id: user.id, visited_at: 2.days.ago, posts_read: 1, mobile: false, time_read: 20)
+      UserVisit.create(user_id: user.id, visited_at: 1.week.ago, posts_read: 1, mobile: false, time_read: 30)
+      UserVisit.create(user_id: user.id, visited_at: 1.year.ago, posts_read: 1, mobile: false, time_read: 40) # Old, should be ignored
+      UserVisit.create(user_id: user2.id, visited_at: 1.minute.ago, posts_read: 1, mobile: false, time_read: 50)
+    end
+
+    it "calculates correctly" do
+      expect(user.recent_time_read).to eq(60)
+      expect(user2.recent_time_read).to eq(50)
+    end
+
+    it "preloads correctly" do
+      User.preload_recent_time_read([user, user2])
+
+      expect(user.instance_variable_get(:@recent_time_read)).to eq(60)
+      expect(user2.instance_variable_get(:@recent_time_read)).to eq(50)
+
+      expect(user.recent_time_read).to eq(60)
+      expect(user2.recent_time_read).to eq(50)
+    end
+  end
 end