迁移数据

db/migrate/20190705011739_add_praises_count_for_challenges.rb

@@ -1,5 +1,5 @@
 class AddPraisesCountForChallenges < ActiveRecord::Migration[5.2]
   def change
-    #add_column :challenges, :praises_count, :integer, :default => 0
+    add_column :challenges, :praises_count, :integer, :default => 0
   end
 end

db/migrate/20190705013203_modify_praises_count_for_challenges.rb

@@ -1,7 +1,7 @@
 class ModifyPraisesCountForChallenges < ActiveRecord::Migration[5.2]
   def change
-    challenges = Challenge.where(nil)
+    challenges = Challenge.where(nil).unscope
-    challenges.each do |c|
+    challenges.find_each do |c|
       praises_count = c.praise_tread.where(praise_or_tread: 1).count
       c.update_column(:praises_count, praises_count)
     end