PERF: Don't include entire post stream when we're loading more posts.

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

@@ -854,13 +854,14 @@ export default RestModel.extend({
     const url = "/t/" + this.get("topic.id") + "/posts.json";
     const data = { post_ids: postIds };
     const store = this.store;
-    return ajax(url, { data }).then(result => {
-      const posts = Ember.get(result, "post_stream.posts");
 
+    return ajax(url, { data }).then(result => {
       if (result.suggested_topics) {
         this.set("topic.suggested_topics", result.suggested_topics);
       }
 
+      const posts = Ember.get(result, "post_stream.posts");
+
       if (posts) {
         posts.forEach(p => this.storePost(store.createRecord("post", p)));
       }

app/serializers/post_stream_serializer_mixin.rb

@@ -3,14 +3,18 @@ require_dependency 'post_serializer'
 require_dependency 'timeline_lookup'
 
 module PostStreamSerializerMixin
-
   def self.included(klass)
     klass.attributes :post_stream
     klass.attributes :timeline_lookup
   end
 
+  def include_stream?
+    true
+  end
+
   def post_stream
-    result = { posts: posts, stream: object.filtered_post_ids }
+    result = { posts: posts }
+    result[:stream] = object.filtered_post_ids if include_stream?
     result[:gaps] = GapSerializer.new(object.gaps, root: false) if object.gaps.present?
     result
   end

app/serializers/topic_view_posts_serializer.rb

@@ -8,4 +8,12 @@ class TopicViewPostsSerializer < ApplicationSerializer
     object.topic.id
   end
 
+  def include_stream?
+    false
+  end
+
+  def include_timeline_lookup?
+    false
+  end
+
 end

spec/serializers/topic_view_posts_serializer_spec.rb

@@ -0,0 +1,26 @@
+require 'rails_helper'
+
+RSpec.describe TopicViewPostsSerializer do
+  let(:user) { Fabricate(:user) }
+  let(:post) { Fabricate(:post) }
+  let(:topic) { post.topic }
+  let(:topic_view) { TopicView.new(topic, user, post_ids: [post.id]) }
+
+  subject do
+    described_class.new(topic_view,
+      scope: Guardian.new(Fabricate(:admin)),
+      root: false
+    )
+  end
+
+  it 'should return the right attributes' do
+    body = JSON.parse(subject.to_json)
+
+    posts = body["post_stream"]["posts"]
+
+    expect(posts.count).to eq(1)
+    expect(posts.first["id"]).to eq(post.id)
+    expect(body["post_stream"]["stream"]).to eq(nil)
+    expect(body["post_stream"]["timeline_lookup"]).to eq(nil)
+  end
+end