UX/PERF: Update readers count when a post from another user is read. Don't fetch the post data again just to update the count. (#8078)

app/assets/javascripts/discourse/controllers/topic.js.es6

@@ -1352,17 +1352,12 @@ export default Ember.Controller.extend(bufferedProperty("model"), {
               })
               .then(() => refresh({ id: data.id, refreshLikes: true }));
             break;
-          case "read":
+          case "read": {
             postStream
-              .triggerChangedPost(data.id, data.updated_at, {
-                preserveCooked: true
-              })
-              .then(() =>
-                refresh({
-                  id: data.id,
-                  refreshReaders: topic.show_read_indicator
-                })
-              );
+              .triggerReadPost(data.id, data.readers_count)
+              .then(() => refresh({ id: data.id, refreshLikes: true }));
+            break;
+          }
           case "revised":
           case "rebaked": {
             postStream

app/assets/javascripts/discourse/models/post-stream.js.es6

@@ -716,6 +716,19 @@ export default RestModel.extend({
     return resolved;
   },
 
+  triggerReadPost(postId, readersCount) {
+    const resolved = Ember.RSVP.Promise.resolve();
+    resolved.then(() => {
+      const post = this.findLoadedPost(postId);
+      if (post && readersCount > post.readers_count) {
+        post.set("readers_count", readersCount);
+        this.storePost(post);
+      }
+    });
+
+    return resolved;
+  },
+
   postForPostNumber(postNumber) {
     if (!this.hasPosts) {
       return;

app/controllers/post_readers_controller.rb

@@ -12,7 +12,7 @@ class PostReadersController < ApplicationController
       .joins(:topic_users)
       .where.not(topic_users: { last_read_post_number: nil })
       .where('topic_users.topic_id = ? AND topic_users.last_read_post_number >= ?', post.topic_id, post.post_number)
-      .where.not(id: [current_user.id, post.user_id])
+      .where.not(id: post.user_id)
 
     readers = readers.map do |r|
       {

app/models/post.rb

@@ -170,6 +170,11 @@ class Post < ActiveRecord::Base
     end
   end
 
+  def readers_count
+    read_count = reads - 1 # Excludes poster
+    read_count < 0 ? 0 : read_count
+  end
+
   def publish_change_to_clients!(type, opts = {})
     # special failsafe for posts missing topics consistency checks should fix,
     # but message is safe to skip

app/models/topic_tracking_state.rb

@@ -357,7 +357,7 @@ SQL
     if topic&.private_message?
       groups = read_allowed_groups_of(topic)
       post = Post.find_by(topic_id: topic.id, post_number: last_read_post_number)
-      trigger_post_read_count_update(post, groups)
+      trigger_post_read_count_update(post, groups, last_read_post_number, user_id)
       update_topic_list_read_indicator(topic, groups, last_read_post_number, user_id, false)
     end
   end
@@ -389,8 +389,9 @@ SQL
     MessageBus.publish("/private-messages/unread-indicator/#{topic.id}", message, user_ids: groups_to_update.flat_map(&:members))
   end
 
-  def self.trigger_post_read_count_update(post, groups)
+  def self.trigger_post_read_count_update(post, groups, last_read_post_number, user_id)
     return if groups.empty?
-    post.publish_change_to_clients!(:read)
+    opts = { readers_count: post.readers_count, reader_id: user_id }
+    post.publish_change_to_clients!(:read, opts)
   end
 end

app/serializers/post_serializer.rb

@@ -459,13 +459,6 @@ class PostSerializer < BasicPostSerializer
     can_review_topic?
   end
 
-  def readers_count
-    read_count = object.reads - 1 # Exclude logged user
-    read_count -= 1 unless yours
-
-    read_count < 0 ? 0 : read_count
-  end
-
 private
 
   def can_review_topic?

spec/requests/post_readers_controller_spec.rb

@@ -57,15 +57,6 @@ describe PostReadersController do
         expect(readers).to be_empty
       end
 
-      it "doesn't include current_user in the readers list" do
-        TopicUser.create!(user: admin, topic: @group_message, last_read_post_number: 3)
-
-         get '/post_readers.json', params: { id: @post.id }
-         reader = JSON.parse(response.body)['post_readers'].detect { |r| r['username'] == admin.username }
-
-         expect(reader).to be_nil
-      end
-
       it "doesn't include users without reading progress on first post" do
         @post.update(post_number: 1)
         TopicUser.create!(user: reader, topic: @group_message, last_read_post_number: nil)