jasl#14 add migration file. improve method set_time_zone.

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# Date:      Wed Aug 14 17:45:34 2019 +0800
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# On branch user-time-zone
# Your branch is up to date with 'origin/user-time-zone'.
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# Changes to be committed:
#	modified:   app/controllers/application_controller.rb
#	new file:   db/migrate/20190809022738_add_user_time_zone.rb
#	new file:   db/migrate/20190814094307_add_user_time_zone.rb
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# Changes not staged for commit:
#	deleted:    db/migrate/20190814094307_add_user_time_zone.rb
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# Untracked files:
#	.generators
#	.idea/
#	.rakeTasks
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app/controllers/application_controller.rb

@@ -60,6 +60,6 @@ def #{s}!(redirect_url: nil)
 
   private
     def set_time_zone
-      Time.zone = current_user.time_zone if current_user and current_user.time_zone.present?
+      Time.zone = current_user.time_zone if current_user&.time_zone&.present?
     end
 end

db/migrate/20190809022738_add_user_time_zone.rb

@@ -0,0 +1,5 @@
+class AddUserTimeZone < ActiveRecord::Migration[6.0]
+  def change
+    add_column :users, :time_zone, :string
+  end
+end

db/migrate/20190814094307_add_user_time_zone.rb

@@ -0,0 +1,5 @@
+class AddUserTimeZone < ActiveRecord::Migration[6.0]
+  def change
+    add_column :users, :time_zone, :string
+  end
+end