迁移字段

app/views/messages/_message.json.jbuilder

@@ -1 +1,2 @@
-json.extract! message, :id, :parent_id, :subject, :created_on, :total_replies_count, :total_praises_count, :praises_count, :visits, :sticky, :is_hidden, :is_public
+json.extract! message, :id, :parent_id, :subject, :created_on, :total_replies_count, :total_praises_count,
+              :is_md, :praises_count, :visits, :sticky, :is_hidden, :is_public

db/migrate/20190720121537_add_is_md_for_messages.rb

@@ -0,0 +1,5 @@
+class AddIsMdForMessages < ActiveRecord::Migration[5.2]
+  def change
+    add_column :messages, :is_md, :boolean, :default => true
+  end
+end

db/migrate/20190720122123_modify_is_md_for_messages.rb

@@ -0,0 +1,7 @@
+class ModifyIsMdForMessages < ActiveRecord::Migration[5.2]
+  def change
+    Message.find_each do |m|
+      m.update_column(:is_md, false)
+    end
+  end
+end