New site setting: `minimum_topics_similar`, allows you to specify a minimum amount

of topics that need to be in the database before it will suggest similar topics as
a user creates a post.

app/controllers/topics_controller.rb

@@ -84,7 +84,11 @@ class TopicsController < ApplicationController
     raise Discourse::InvalidParameters.new(:title) if title.length < SiteSetting.min_title_similar_length
     raise Discourse::InvalidParameters.new(:raw) if raw.length < SiteSetting.min_body_similar_length
 
-    topics = Topic.similar_to(title, raw, current_user)
+    # Only suggest similar topics if the site has a minimmum amount of topics present.
+    if Topic.count > SiteSetting.minimum_topics_similar
+      topics = Topic.similar_to(title, raw, current_user)
+    end
+
     render_serialized(topics, BasicTopicSerializer)
   end
 

app/models/site_setting.rb

@@ -222,6 +222,8 @@ class SiteSetting < ActiveRecord::Base
   client_setting(:topic_views_heat_medium, 2000)
   client_setting(:topic_views_heat_high,   5000)
 
+  setting(:minimum_topics_similar, 50)
+
   def self.generate_api_key!
     self.api_key = SecureRandom.hex(32)
   end

config/locales/server.en.yml

@@ -383,7 +383,7 @@ en:
     memory_warning: 'Your server is running with less than 1 GB of total memory. At least 1 GB of memory is recommended.'
     facebook_config_warning: 'The server is configured to allow signup and log in with Facebook (enable_facebook_logins), but the app id and app secret values are not set. Go to <a href="/admin/site_settings">the Site Settings</a> and update the settings. <a href="https://github.com/discourse/discourse/wiki/The-Discourse-Admin-Quick-Start-Guide#enable-facebook-logins" target="_blank">See this guide to learn more</a>.'
     cas_config_warning: 'The server is configured to allow signup and log in with CAS (enable_cas_logins), but the hostname and domain name values are not set.'
-    twitter_config_warning: 'The server is configured to allow signup and log in with Twitter (enable_twitter_logins), but the key and secret values are not set. Go to <a href="/admin/site_settings">the Site Settings</a> and update the settings. <a href="https://github.com/discourse/discourse/wiki/The-Discourse-Admin-Quick-Start-Guide#enable-twitter-logins" target="_blank">See this guide to learn more</a>.'
+    twitter_config_warning: 'The server is configured to allow signup and log in with Twitter (enable_twitter_logins), but the key and secret values are not set. Go to <a href="/admin/site_site_settings">the Site Settings</a> and update the settings. <a href="https://github.com/discourse/discourse/wiki/The-Discourse-Admin-Quick-Start-Guide#enable-twitter-logins" target="_blank">See this guide to learn more</a>.'
     github_config_warning: 'The server is configured to allow signup and log in with GitHub (enable_github_logins), but the client id and secret values are not set. Go to <a href="/admin/site_settings">the Site Settings</a> and update the settings. <a href="https://github.com/discourse/discourse/wiki/The-Discourse-Admin-Quick-Start-Guide" target="_blank">See this guide to learn more</a>.'
     failing_emails_warning: 'There are %{num_failed_jobs} email jobs that failed. Check your config/environments/production.rb file and ensure that the config.action_mailer settings are correct. <a href="/sidekiq/retries" target="_blank">See the failed jobs in Sidekiq</a>.'
     default_logo_warning: "You haven't customized the logo images for your site. Update logo_url, logo_small_url, and favicon_url in the <a href='/admin/site_settings'>Site Settings</a>."
@@ -623,6 +623,8 @@ en:
     pop3s_polling_username: "The username for the POP3S account to poll for email"
     pop3s_polling_password: "The password for the POP3S account to poll for email"
 
+    minimum_topics_similar: "How many topics need to exist in the database before similar topics are presented."
+
 
   notification_types:
     mentioned: "%{display_username} mentioned you in %{link}"

spec/controllers/topics_controller_spec.rb

@@ -161,18 +161,40 @@ describe TopicsController do
       -> { xhr :get, :similar_to, title: title, raw: raw }.should raise_error(Discourse::InvalidParameters)
     end
 
-    it "delegates to Topic.similar_to" do
-      Topic.expects(:similar_to).with(title, raw, nil).returns([Fabricate(:topic)])
-      xhr :get, :similar_to, title: title, raw: raw
-    end
+    describe "minimum_topics_similar" do
 
-    context "logged in" do
-      let(:user) { log_in }
+      before do
+        SiteSetting.stubs(:minimum_topics_similar).returns(30)
+      end
 
-      it "passes a user throught if logged in" do
-        Topic.expects(:similar_to).with(title, raw, user).returns([Fabricate(:topic)])
+      after do
         xhr :get, :similar_to, title: title, raw: raw
       end
+
+      describe "With enough topics" do
+        before do
+          Topic.stubs(:count).returns(50)
+        end
+
+        it "deletes to Topic.similar_to if there are more topics than `minimum_topics_similar`" do
+          Topic.expects(:similar_to).with(title, raw, nil).returns([Fabricate(:topic)])
+        end
+
+        describe "with a logged in user" do
+          let(:user) { log_in }
+
+          it "passes a user through if logged in" do
+            Topic.expects(:similar_to).with(title, raw, user).returns([Fabricate(:topic)])
+          end
+        end
+
+      end
+
+      it "does not call Topic.similar_to if there are fewer topics than `minimum_topics_similar`" do
+        Topic.stubs(:count).returns(10)
+        Topic.expects(:similar_to).never
+      end
+
     end
 
   end