Use `add_directory_column` API to add solutions count to user directory (#137)

config/locales/client.en.yml

@@ -4,6 +4,7 @@ en:
       alt:
         solved:
           accepted_notification: "accepted"
+    solutions: "Solutions"
 
     solved:
       title: "Solved"

db/migrate/20210609171830_add_solutions_to_directory_items.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AddSolutionsToDirectoryItems < ActiveRecord::Migration[6.1]
+  def change
+    add_column :directory_items, :solutions, :integer, default: 0
+  end
+end

plugin.rb

@@ -613,6 +613,26 @@ SQL
     options[:refresh_stream] = true if old_category_allows != new_category_allows
   end
 
+  query = "
+    WITH x AS (SELECT
+      u.id user_id,
+      COUNT(DISTINCT ua.id) AS solutions
+      FROM users AS u
+      INNER JOIN user_actions AS ua ON ua.user_id = u.id AND ua.action_type = #{UserAction::SOLVED} AND COALESCE(ua.created_at, :since) > :since
+      WHERE u.active
+        AND u.silenced_till IS NULL
+        AND u.id > 0
+      GROUP BY u.id
+    )
+    UPDATE directory_items di SET
+      solutions = x.solutions
+    FROM x
+    WHERE x.user_id = di.user_id
+    AND di.period_type = :period_type
+    AND di.solutions <> x.solutions
+  "
+  add_directory_column("solutions", query: query)
+
   add_to_class(:composer_messages_finder, :check_topic_is_solved) do
     return if !SiteSetting.solved_enabled || SiteSetting.disable_solved_education_message
     return if !replying? || @topic.blank? || @topic.private_message?