Cache deletion times on Post

Closes #96

app/models/deletion_log.rb

@@ -7,4 +7,10 @@ class DeletionLog < ApplicationRecord
       ActionCable.server.broadcast "api_deletion_logs", { deletion_log: JSON.parse(DeletionLogsController.render(locals: {deletion_log: self}, partial: 'deletion_log.json')) }
     end
   end
+
+  after_create do
+    if is_deleted and post.deleted_at.nil?
+      post.update(:deleted_at => created_at)
+    end
+  end
 end

db/migrate/20170217051750_add_deleted_at_to_posts.rb

@@ -0,0 +1,5 @@
+class AddDeletedAtToPosts < ActiveRecord::Migration[5.0]
+  def change
+    add_column :posts, :deleted_at, :datetime
+  end
+end

db/migrate/20170217064146_migrate_to_cached_deletion_times.rb

@@ -0,0 +1,12 @@
+class MigrateToCachedDeletionTimes < ActiveRecord::Migration[5.0]
+  def change
+    sql = <<-SQL
+      UPDATE `posts`
+      INNER JOIN
+        (SELECT `deletion_logs`.`post_id`, min(`deletion_logs`.`created_at`) as min_dl FROM `deletion_logs` WHERE `is_deleted` = true GROUP BY `deletion_logs`.`post_id`) dl on dl.post_id = posts.id
+      SET `posts`.`deleted_at` = dl.min_dl
+    SQL
+
+    ActiveRecord::Base.connection.execute(sql)
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170215003244) do
+ActiveRecord::Schema.define(version: 20170217064146) do
 
   create_table "api_keys", force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci" do |t|
     t.datetime "created_at",  null: false
@@ -188,6 +188,7 @@
     t.boolean  "is_fp",                                   default: false
     t.boolean  "is_naa",                                  default: false
     t.integer  "revision_count"
+    t.datetime "deleted_at"
     t.index ["created_at"], name: "index_posts_on_created_at", using: :btree
     t.index ["link"], name: "index_posts_on_link", length: { link: 191 }, using: :btree
   end